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NITRO-EXPLOSIVES
/fori*/- 1 10k
it NlTRO-EXP LOS IVES
A PRACTICAL TREATISE
CONCERNING THE
PROPERTIES, MANUFACTURE, AND ANALYSIS OF
NITRATED SUBSTANCES, INCLUDING THE FULMINATES,
SMOKELESS POWDERS, AND CELLULOID
■ P. GERALD SAXFORD, F.I.C., F.C.S.
Public Analyst to the Borough of Penzance ; late Consulting Chemist to the Cotton Powde
Company Limited ; and formerly Resident Chemist at the Stowmarket Works
of the New Explosives Company Limited, and the Hayle Works
of the National Explosive Company Limited
SeconO JEfcitton, IRewseD an& Enlarged
LONDON CROSBY LOCK WOOD AND SON
7 STATIONERS' HALL COURT, LUDGATE HILL I906
-U
i'V"
D. VAN NOSTRANB COMPANY
NEW Y«RI
Bao
The Library
The University of North Carolina
Chapel Hill
Printed at The Darien Press, Edinburgh.
PREFACE.
T N compiling the following treatise, my aim has * been to give a brief but thoroughly practical account of the properties, manufacture, and methods of analysis of the various nitro-explosives now so largely used for mining and blasting purposes and as propulsive agents ; and it is believed that the account given of the manufacture of nitro-glycerine and of the gelatine dynamites will be found more complete than in any similar work yet published in this country.
For many of the facts and figures contained in the chapter on Smokeless Powders I am indebted to (amongst others) the late Mr J. D. Dougall and Messrs A. C. Ponsonby and H. M. Chapman, F.C.S. ; and for details with regard to Roburite to Messrs H. A. Krohn and W. J. Orsman, F.I.C. To these gentlemen my cordial thanks are due. Among the authorities which have been consulted in the general preparation of the work may be mentioned the Journals of the Chemical Society, the Society of Chemical Industry, the United States
_Q 1 —
VI PREFACE.
Naval Institute, and the Royal Artillery Institution. I have also referred to several volumes of the periodical publication Arms and Explosives ; to various papers by Sir Frederick Abel, Bart., F.R.S., and General Wardell, R.A., on Gun-Cotton ; to "Modern Artillery," by Capt. Lloyd, R.N., and A. G. Hadcock, R.A. ; to the late Colonel Cundill's " Dictionary of Explosives " ; as well as to the works of Messrs Eissler, Berthelot, and others.
The illustrations have been prepared chiefly from my own drawings. A few, however, have been taken (by permission) from the pages of Arms and Explosives, or from other sources which are acknowledged in the text.
P. G. S.
The Laboratory,
20 Cullum Street, E.C May 1 89 6.
PREFACE TO THE SECOND EDITION
IN the preparation of the Second Edition of this work, I have chiefly made use of the current technical journals, especially of the Journal of the Society of Chemical Industry. The source of my information has in every case been acknowledged.
I am also indebted to several manufacturers of explosives for information respecting their special products — among others the New Explosives Com- pany Ltd. ; Messrs Curtis's and Harvey Ltd. ; The Schultze Gunpowder Company Ltd. ; and Mr W. D. Borland, F.I.C., of the E. C. Powder Company Ltd.
To my friend Mr A. Stanley Fox, F.C.S., of Faversham, my best thanks are also due for his help in many departments, and his kindness in pointing out several references.
The chapter on Smokeless Powders has been considerably enlarged and (as far as possible) brought up to date ; but it has not always been possible to give the process of manufacture or even the com- position, as these details have not, in several cases, been made public.
P. GERALD SANFORD.
London, June 1906.
TABLE OF CONTENTS.
CHAPTER I.— INTRODUCTION
I'Ai.i-:-,
The Nitro-Explosives — Substances that have been Nitrated — The Danger Area — Systems of Professors Lodge, Zenger, and Melsens for the Protection of Buildings from Lightning, &c. - 1-16
CHAPTER II.— NITRO-GLYCERINE.
Properties of Nitro-Glycerine — Manufacture — Nitration — Separa- tion— Washing and Filtering — Drying, Storing, &c. — The Waste Acids — Their Treatment — Nitric Acid Plants - - 17-46
CHAPTER III.-NITRO-CELLULOSE, &c.
Cellulose Properties — Discovery of Gun-Cotton — Properties of Gun-Cotton — Varieties of Soluble and Insoluble Gun- Cottons — Manufacture of Gun-Cotton — Dipping and Steep- ing— Whirling Out the Acid — Washing, Boiling, Pulping, Compressing — The Waltham Abbey Process — Le Bouchet Process — Granulation of Gun-Cotton — Collodion-Cotton — Manufacture — Acid Mixture Used — Cotton Used, &c. — Nitrated Gun-Cotton — Tonite — Dangers in Manufacture of Gun-Cotton — Trench's Fire-Extinguishing Compound — Uses of Collodion-Cotton — Celluloid — Manufacture, &c. — Nitro- Starch, Nitro-Jute, and Nitro-Mannite - - - - - 47-111
CHAPTER IV.— DYNAMITE.
Kieselguhr Dynamite — Classification of Dynamites — Properties and Efficiency of Ordinary Dynamite — Other forms of Dynamite — Gelatine and Gelatine Dynamites, Suitable Gun- Cotton for, and Treatment of — Other Materials Used — Com- position of Gelignite — Blasting Gelatine — Gelatine Dynamite — Absorbing Materials — Wood Pulp — Potassium Nitrate, &c. — Manufacture, &c. — Apparatus Used — The Properties of the Gelatine Compounds -------- 112-131
b
X TABLE OF CONTENTS.
PAGES
CHAPTER V.— NITRO-BENZOL, ROBURITE, BELLITE, PICRIC ACID, &c
Explosives derived from Benzene — Toluene, Nitro-Benzene, Di- and Tri-Nitro — Roburite : Properties and Manufacture — Bellite : Properties, &c. — Securite — Tonite No. 3 — Nitro- Toluene — Nitro-Naphthalene — Faversham Powder — Ammo- nite— Electronite — Sprengel's Explosives — Picric Acid — Picrates — Picric Powders — Melinite — Abel's Mixture — Brugere's Powders — Tri-nitro-cresol ----- 132-167 The Fulminates.
Composition, Formula, Preparation, Danger of, &c. — Detonators :
Sizes, Composition, Manufacture — Fuses, &c. - - - 159-167
CHAPTER VI.— SMOKELESS POWDERS IN GENERAL. Cordite— Axite— Ballistite— U.S. Naval Powder— Scbultze's E.C. Powder — Indurite — Vielle Poudre — Walsrode and Cooppal Powders — Amberite — Troisdorf — B. N. Powder — Wetterin — Normal Powder — Maximite — Picric Acid Powders, &c. &c. - 16S-196
CHAPTER VII.— ANALYSIS OF EXPLOSIVES. Kieselguhr Dynamite — Gelatine Compounds — Tonite — Cordite — Vaseline — Acetone — Scheme for Analysis of Explosives — Nitro-Cotton — Solubility Test — Non-Nitrated Cotton- Alkalinity — Ash and Inorganic Matter — Determination pf Nitrogen — Lunge, Champion and Pellet's, Schultze-Tieman, and Kjeldahl's Methods — Celluloid — Picric Acid and Picrates — Resinous and Tarry Matters — Sulphuric Acid and Hydrochloric Acid and Oxalic Acid — Nitric Acid — Inorganic Impurities — General Impurities and Adulterations — Potassium Picrate, &c. — Picrates of the Alkaloids — Analysis of Glycerine — Residue — Silver Test — Nitration — Total Acid Equivalent — Neutrality — Free Fatty Acids — Combined Fatty Acids — Impurities — Oleic Acid — Sodium Chloride — Determination of Glycerine — Waste Acids — Sodium Nitrate — Mercury Fulmi- nate— Cap Composition — Table for Correction of Volumes of Gases, for Temperature and Pressure ----- 197-246
CHAPTER VIII.— FIRING POINT OF EXPLOSIVES, HEAT TESTS, &c.
Horsley's Apparatus — Table of Firing Points — The Government Heat Test Apparatus, &c, for Dynamites, Nitro-Glycerine, Nitro-Cotton, and Smokeless Powders — Guttmann's Heat Test — Liquefaction and Exudation Tests — Page's Regulator for Heat Test Apparatus —Specific Gravities of Explosives — Will's Test for Nitro-Cellulose — Table of Temperature of Detonation, Sensitiveness, &c. ------ 247-271
TABLE OF CONTENTS. XI
PAGES
CHAPTER IX.— THE DETERMINATION OF THE RELATIVE STRENGTH OF EXPLOSIVES.
Effectiveness of an Explosive — High and Low Explosives — Theo- retical Efficiency — MM. Roux and Sarrau's Results — Abel and Noble's — Nobel's Ballistic Test — The Mortar — Pressure or Crusher Gauge — Calculation Volume of Gas Evolved, Sec. — Lead Cylinders — The Foot-Pounds Machine — Noble's Pres- sure Gauge — Lieut. Walke's Results — Calculation of Pressure Developed by Dynamite and Gun-Cotton — M'Nab's and Ristori's Results of Heat Developed by the Explosion of Various Explosives — Composition of some of the Explosives in Common Use for Blasting, See. ... - - 272-294
INDEX - - - - - 295-300
LIST OF ILLUSTRATIONS.
FIG. PAGE
Frontispiece — Danger Building showing Protecting Mounds.
1. Section of Nitro-Glycerine Conduit ------ 7
2. Melsens System of Lightning Conductors 10
3. French System- - - - - - - - - - 11
4a & \b. English Government System - - - - - - 12
5. Upper Portion of Nitrator for Nitro-Glycerine - - - - 27
6. Small Nitrator - - - - - - - - - - 31
7. Nathan's Nitrator --------- 33
8. Nitro-Glycerine Separator -------- 36
9. Nitro-Glycerine Filtering Apparatus ------ 37
10. Cotton-Waste Drier --------- 59
11. Dipping Tank - - - - - - - - - - 61
12. Cooling Pits - - - - - - - - - - 61
13. Steeping Pot for Gun-Cotton - - - - - - - 62
14. Hydro-Extractor or Centrifugal Drier 62
15a & 15& Gun-Cotton Beater 64,65
16a. Poacher for Pulping Gun-Cotton 65
i65. Plan of same 66
16c. Another form of Poacher - - 66
17 & 18. Compressed Gun-Cotton ------- 68
19. Hydraulic Press ......... 70
20. Thomson's Apparatus — Elevation 74
21. Elevation Plan ---------- 75
Xll LIST OF ILLUSTRATIONS.
FIG. PAGES
22. Trench's Safety Cartridge -------- 89
23. Vessel used in Nitrating Paper ------- 96
24. Cage ditto — White & Schupphaus' Apparatus - - - - 97
25. Do. do. do. - - - - 97
26 & 27. Nitrating Pot for Celluloid 97
28 & 29. Plunge Tank in Plan and Section ----- 98
30. Messrs Werner, Pfleiderer & Perkins' Mixing Machine - - 124
31. M 'Roberts' Mixing Machine for Blasting Gelatine - - 125
32. Plan of same - - - - - - - - - 127
33. Cartridge Machine for Gelatines - - - - - - 128
34. Cartridge fitted with Fuse and Detonator ----- 166
35. Gun-Cotton Primer --------- 166
36. Electric Firing Apparatus - - - - - - ' - 167
37. Metal Drum for Winding Cordite - 171
38. Ten-Stranding - - - - - - - - - 171
39. Curve showing relation between Pressures of Cordite and Black
Powder, by Professor Vivian Lewes - - - - 175
40. Marshall's Apparatus for Moisture in Cordite - - 207
41. Lunge's Nitrometer - - - - - - - - » - 220
42. Modified do. 222
43. Horn's Nitrometer - - 222
44. Schultze-Tieman Apparatus for Determination of Nitrogen in
Gun-Cotton ---------- 225
45. Decomposition Flask for Schultze-Tieman Method - - - 226
46. Abel's Heat Test Apparatus ------- 249
47. Apparatus for Separation of Nitro -Glycerine from Dynamite - 252
48. Test Tube arranged for Heat Test 252
49. Page's Regulator --------- 260
50. Do. showing Bye-Pass and Cut-off Arrangement - 260
51. Will's Apparatus 263
52 & 53. Curves obtained 266-267
54. Dynamite Mortar - 275
55. Quinan's Pressure Gauge -------- 278
56. Steel Punch and Lead Cylinder for Use with Pressure Gauge - 279
57. Micrometer Calipers for Measuring Thickness of Lead Cylinders 280
58. Section of Lead Cylinders before and after Explosion - - - 281
59. Noble's Pressure Gauge -------- 282
60. Crusher Gauge ---------- 284
NITRO-EXPLOSIVES.
CHAPTER I. INTRODUCTORY.
The Nitro-Explosives — Substances that have been Nitrated — The Danger Area — Systems of Professors Lodge, Zenger, and Melsens for the Protection of Buildings from Lightning, &c.
The manufacture of the various nitro-explosives has made great advances during late years, and the various forms of nitro-compounds are gradually replacing the older forms of explosives, both for blasting purposes and also for propul- sive agents, under the form of smokeless powders. The nitro-explosives belong to the so-called High Explosives, and may be defined as any chemical compound possessed of explosive properties, or capable of combining with metals to form an explosive compound, which is produced by the chemical action of nitric acid, either alone or mixed with sulphuric acid, upon any carbonaceous substance, whether such compound is mechanically mixed with other substances or not.*
The number of compounds and mixtures included under this definition is very large, and they are of very different chemical composition. Among the substances that have been nitrated are : — Cellulose, under various forms, e.g.,
* Definition given in Order of Council, No. i, Explosives Act, 1875.
A
2 NITRO-EXrLOSIVES.
cotton, lignin, &c. ; glycerine, benzene, starch, jute, sugar, phenol, wood, straw, and even such substances as treacle and horse-dung. Some of these are not made upon the large scale, others are but little used. Those of most im- portance are nitro - glycerine and nitro - cellulose. The former enters into the composition of all dynamites, and several smokeless powders ; and the second includes gun- cotton, collodion-cotton, nitrated wood, and the majority of the smokeless powders, which consist generally of nitro-cotton, nitro-lignin, nitro-jute, &c. &c, together with metallic nitrates, or nitro-glycerine.
The nitro-explosives consist generally of some organic substance in which the N02 group, known as nitryl, has been substituted in place of hydrogen.
[OH Thus in glycerine, C3H5-|OH, which is a tri-hydric
' [OH
alcohol, and which occurs very widely distributed as the alcoholic or basic constituent of fats, the hydrogen atoms are replaced by the NO,2 group, to form the highly explo- sive compound, nitro-glycerine. If one atom only is thus
[ON02
ius, C,H6J0H
displaced, the mono-nitrate is formed tin
"OH
and if the three atoms are displaced, C3H5(ON00)3, or the tri-nitrate, is formed, which is commercial nitro-glycerine.
Another class, the nitro-celluloses, are formed from cellulose, C6H10O5, which forms the groundwork of all vegetable tissues. Cellulose has some of the properties of the alcohols, and forms ethereal salts when treated with nitric and sulphuric acids. Thehexa-nitrate, or gun-cotton, has the formula, C12HU04(0N02)6; and collodion-cotton, pyroxylin, &c, form the lower nitrates, i.e., the tetra- and penta-nitrates. These last are soluble in various solvents, such as ether-alcohol and nitro-glycerine, in which the
NITROCOMPOUNDS. 3
hexa-nitrate is insoluble. They all dissolve, however, in acetone and acetic ether.
The solution of the soluble varieties in ether-alcohol is known as collodion, which finds many applications in the arts. The hydrocarbon benzene, CGHC, prepared from the light oil obtained from coal-tar. when nitrated forms nitro- benzenes, such as mono-nitro-benzene, C0H-NOo, and di- nitro-benzene, C0H4(NOo)2, in which one and two atoms are replaced by the NO, group. The latter of these com- pounds is used as an explosive, and enters into the compo- sition of such well-known explosives as roburite, &c. The presence of nitro groups in a substance increases the difficulty of further nitration, and in any case not more than three nitro groups can be introduced into an aromatic compound, or the phenols. All aromatic compounds with the general formula, C6H4X.7, give, however, three series. They are called ortho, meta, or para compounds, depending upon the position of N02 groups introduced.
Certain regularities have been observed in the formation of nitro-compounds. If, for example, a substance contains alkyl or hydroxyl groups, large quantities of the para com- pound are obtained, and very little of the ortho. The substitution takes place, however, almost entirely in the meta position, if a nitro, carboxyl, or aldehyde group be present. Ordinary phenol, C6H..OH, gives para- and ortho-nitro-phenol ; toluene gives para- and ortho-nitro- toluene ; but nitro-benzene forms meta-di-nitro-benzene and benzoic acid, meta-nitro-benzoic acid.*
If the graphic formula of benzene be represented thus (No. 1), then the positions 1 and 2 represent the ortho, 1 and 3 the meta, and 1 and 4 the para compounds. When the body phenol, CGH5.OH, is nitrated, a compound is formed known as tri-nitro-phenol, or picric acid, CGH0(N00)3OH, which is used very extensively as an explosive, both as
*" Organic Chemistry," Prof. Hjelt, Translated bv ]. B. Tingle, Ph.D.
4 NITRO-EXPLOSIVES.
picric acid and in the form of picrates. Another nitro body that is used as an explosive is nitro-naphthalene, C10HG(NO.,).2, in roburite, securite, and other explosives of this class. The hexa-nitro-mannite, C6H8(ON02)6, is formed
H.l
S \
H.C CH.2
H.C CH.3
NO
NO.
C MEtA-.DINlT.RO -BENZENE
H.4 N°2.
N ? i .
by treating a substance known as mannite, CcHs(OH)c, an alcohol formed by the lactic acid fermentation of sugar and closely related to the sugars, with nitric and sulphuric acids. It is a solid substance, and very explosive ; it contains 18.58 per cent, of nitrogen.
Nitro-starch has also been used for the manufacture of an explosive. Muhlhauer has described {Ding. Poly. Jour., 73, 137-143) three nitric ethers of starch, the tetra-nitro- starch, C12H1606(ON02)4, the penta- and hexa-nitro-starch. They are formed by acting upon potato starch dried at 100° C. with a mixture of nitric and sulphuric acids at a temperature of 20° to 250 C. Rice starch has also been used in its production. Muhlhauer proposes to use this body as a smokeless powder, and to nitrate it with the spent mixed acids from the manufacture of nitro-glycerine. This substance contains from 10.96 to 11.09 Per cent, of nitrogen. It is a white substance, very stable and soluble even in cold nitro-glycerine.
The explosive bodies formed by the nitration of jute have been studied by Messrs Cross and Bevan, and also
NITRO-JUTE AND NITROSTARCH. 5
by Miihlhauer. The former chemists give jute the formula C12H1809, and believe that its conversion into a nitro- compound takes place according to the equation —
C12H1809+3HN03 = 3H20 + C12H1506(N03)3.
This is equivalent to a gain in weight of 44 per cent, for the tri-nitrate, and 58 per cent, for the tetra-nitrate. The formation of the tetra-nitrate appears to be the limit of nitration of jute fibre. Messrs Cross and Bevan say, " In other words, if we represent the ligno-cellulose molecule by a C12 formula, it will contain four hydroxyl (OH) groups, or two less than cellulose similarly represented." It contains 1 1.5 per cent, of nitrogen. The jute nitrates resemble those of cellulose, and are in all essential points nitrates of ligno- cellulose.
Nitro-jute is used in the composition of the well-known Cooppal Smokeless Powders. Cross and Bevan are of opinion that there is no very obvious advantage in the use of lignified textile fibres as raw materials for explosive nitrates, seeing that a number of raw materials containing cellulose (chiefly as cotton) can be obtained at from ,£10 to .£25 a ton, and yield also 150 to 170 per cent, of explosive material when nitrated (whereas jute only gives 154.4 per cent.), and are in many ways superior to the products obtained from jute. Nitro-lignin, or nitrated wood, is, however, largely used in the composition of a good many of the smokeless powders, such as Schultze's, the Smokeless Powder Co.'s products, and others.
The Danger Area. — That portion of the works that is devoted to the actual manufacture or mixing of explosive material is generally designated by the term " danger area," and the buildings erected upon it are spoken of as " danger buildings." The best material of which to construct these buildings is of wood, as in the event of an explosion they will offer less resistance, and will cause much less danger than brick or stone buildings. When an explosion of
6 NITRO-EXPLOSIVES.
nitroglycerine or dynamite occurs in one of these buildings, the sides are generally blown out, and the roof is raised some considerable height, and finally descends upon the blown-out sides. If, on the other hand, the same explosion had occurred in a strong brick or stone building, the walls of which would offer a much larger resistance, large pieces of brickwork would probably have been thrown for a considerable distance, and have caused serious damage to surrounding buildings.
It is also a very good plan to surround all danger buildings with mounds of sand or earth, which should be covered with turf, and of such a height as to be above the roof of the buildings that they are intended to protect (see frontispiece).* These mounds are of great value in confining the force of the explosion, and the sides of the buildings being thrown against them are prevented from travelling any distance. In gunpowder works it is not unusual to surround the danger buildings with trees or dense underwood instead of mounds. This would be of no use in checking the force of explosion of the high explosives, but has been found a very useful precaution in the case of gunpowder.
In Great Britain it is necessary that all danger buildings should be a specified distance apart ; a license also must be obtained. The application for a license must give a plan (drawn to scale) of the proposed factory or magazine, and the site, its boundaries, and surroundings, and distance the building will be from any other buildings or works, &c,
* At the Baelen Factory, Belgium, the danger buildings are erected on a novel plan. They are circular in ground plan and lighted entirely from the roof by means of a patent glass having wire-netting in it, and which it is claimed will not let a splinter fall, even if badly cracked. The mounds are then erected right up against the walls of the building, exceeding them in height by several metres. For this method of con- struction it is claimed that the force exerted by an explosion will expand itself in a vertical direction ("Report on Visits to Certain Explosive Factories," H.M. Inspectors, 1905).
ARRANGEMENT OF DANGER AREA. /
also the character, and construction of all the mounds, and nature of the processes to be carried on in the factory or building.*
The selection of a site for the danger area requires some attention. The purpose for which it is required, that is, the kind of explosive that it is intended to manufacture, must be taken into consideration. A perfectly level piece
Fig. i. — Section of Nitro-Glycerine Conduit. a, lid ; b, lead lining ; c, cinders.
of ground might probably be quite suitable for the purpose of erecting a factory for the manufacture of gun-cotton or gunpowder, and such materials, but would be more or less unsuitable for the manufacture of nitro-glycerine, where a number of buildings are required to be upon different levels, in order to allow of the flow of the liquid nitro-glycerine from one building to another through a system of conduits. These conduits (Fig. i), which are generally made of wood and lined with lead, the space between the woodwork and the lead lining, which is generally some 4 or 5 inches, being filled with cinders, connect the various buildings, and should slope gently from one to the other. It is also desirable that, as far as possible, they should be protected by earth- work banks, in the same way as the danger buildings themselves. They should also be provided with covers, which should be whitewashed in hot weather.
A great deal of attention should be given to these conduits, and they should be very frequently inspected. Whenever it is found that a portion of the lead lining requires repairing, before cutting away the lead it should
* Explosives Act, 38 Vict. ch. 17.
S NITRO-EXPLOSIVES.
be very carefully washed, for several feet on either side of the portion that it is intended to remove, with a solution of caustic soda or potash dissolved in methylated spirit and water, and afterwards with water alone. This decomposes the nitro-glycerine forming glycerine and potassium nitrate. It will be found that the mixed acids attack the lead rather quickly, forming sulphate and nitrate of lead, but chiefly the former. It is on this account that it has been proposed to use pipes made of guttapercha, but the great drawback to their use is that in the case of anything occurring inside the pipes, such as the freezing of the nitro-glycerine in winter, it is more difficult to find it out, and the condition of the inside cannot be seen, whereas in the case of wooden conduits it is an easy matter to lift the lids along the whole length of the conduit.
The buildings which require to be connected by con- duits are of course those concerned with the manufacture of nitro-glycerine. These buildings are — (i) The nitrating house; (2) the separating house; (3) the filter house; (4) the secondary separator ; (5) the deposit of washings ; (6) the settling or precipitation house ; and each of these buildings must be on a level lower than the preceding one, in order that the nitro-glycerine or acids may flow easily from one building to the next. These buildings are, as far as possible, best placed together, and away from the other danger buildings, such as the cartridge huts and dynamite mixing houses, but this is not essential.
All danger buildings should be protected by a light- ning conductor, or covered with barbed wire, as suggested by Professor Sir Oliver J. Lodge, F.R.S., Professors Zenger, of Prague, and Melsens, of Brussels, and everything possible should be done to keep them as cool as possible in the summer. With this object they should be made double, and the intervening space filled with cinders. The roof also should be kept whitewashed, and the windows painted over thinly with white paint. A ther- mometer should be suspended in every house. It is very
PROTECTION OF DANGER BUILDINGS. 9
essential that the floors of all these buildings should be washed every day before the work-people leave. In case any nitro-glycerine is spilt upon the floors, after sponging it up as far as possible, the floor should be washed with an alcoholic solution of soda or potash to decompose the nitro-glycerine, which it does according to the equation* —
C3H5(N03)3+ 3KOH = C3Hs03 + 3KNO3.
Every one employed in the buildings should wear list or sewn leather shoes, which of course must be worn in the buildings only. The various houses should be connected by paths laid with cinders, or boarded with planks, and any loose sand about the site of the works should be covered over with turf or cinders, to prevent its blowing about and getting into the buildings. It is also of import- ance that stand pipes should be placed about the works with a good pressure of water, the necessary hose being kept in certain known places where they can be at once got at in the case of fire, such as the danger area laboratory, the foreman's office, &c. It is also desirable that the above precautions against fire should be tested once a week. With regard to the heating of the various buildings in the winter, steam pipes only should be used, and should be brought from a boiler-house outside the danger area, and should be covered with kieselguhr or fossil meal and tarred canvas. These pipes may be supported upon poles. A stove of some kind should be placed in the corner of each building, but it must be entirely covered in with woodwork, and as small a length of steam pipes should be within the building as possible.
In the case of a factory where nitro-glycerine and dynamite are manufactured, it is necessary that the work- people should wear different clothes upon the danger area than usual, as they are apt to become impregnated with nitro-glycerine, and thus not very desirable or safe to wear
* See also Bertbelot, Contptes Remius, 1900, 131 [12], 519-521.
IO
NITRO-EXPLOSIVES.
outside the works. It is also necessary that these clothes should not contain any pockets, as this lessens the chance of matches or steel implements being taken upon the danger area. Changing houses, one for the men, and another for the girls, should also be provided. The tools used upon the danger area should, whenever the building is in use, or contains explosives, be made of phosphor bronze or brass, and brass nails or wooden pegs should be used in the construction of all the buildings.
kA^sA
Fig. 2. — Melsens System of Lightning Conductors.
Lightning Conductors. — The Explosive Substances Act, 38 Vict. ch. 1 7, clause 10, says, " Every factory magazine and expense magazine in a factory, and every danger build- ing in a magazine, shall have attached thereto a sufficient lightning conductor, unless by reason of the construction by excavation or the position of such magazine or building, or otherwise, the Secretary of State considers a conductor unnecessary, and every danger building in a factory shall, if so required by the Secretary of State, have attached thereto a sufficient lightning con- ductor."
The exact form of lightning conductor most suitable for explosive works and buildings has not yet been defin- itely settled. Lightning-rod engineers favour what is known as the Melsens system, due to Professor Melsens, of Brussels, and Professor Zenger, of Prague, but first suggested by the late Professor Clerk-Maxwell. In a paper read before the British Association, Clerk-Maxwell proposed to protect powder-magazines from the effects of lightning by completely surrounding or encasing them with sheet metal, or a cage of metallic conductors. There were, however, several objections to his system as he left it.
LIGHTNING CONDUCTORS. II
Professor Melsens* has, while using the idea, made several important alterations. He has multiplied the terminals, the conductors, and the earth-connections. His terminals are very numerous, and assume the form of an aigrette or brush with five or seven points, the central point being a little higher than the rest, which form with it an angle of 45°. He employs for the most part galvanised- iron wire. He places all metallic bodies, if they are of any considerable size, in communication with the conducting system in such a manner as to form closed metallic circuits. His system is illustrated in Fig. 2, taken from Anns and Explosives.
This system is a near approximation to J. C. Maxwell's cage. The system was really designed for the protection of powder-magazines or store buildings placed in very exposed situations. Zenger's system is identical with that of Melsens, and has been extensively tried by the Austrian military authorities, and Colonel Hess has reported upon the absolute safety of the system.
The French system of protecting powder-magazines is shown in Fig. 3, where there are no brush terminals or aigrettes. The French mili- tary authorities also protect magazines by erecting two or more lightning - rods on poles of sufficient height placed close to, but not touch- FlG 3._French System of
ing, the Walls Of the magazine. Lightning Conductors.
These conductors are joined below the foundations and earthed as usual.
In the instructions issued by the Government, it is stated that the lightning-rods placed upon powder-mills should be of such a height, and so situated, that no danger is incurred in igniting the powder-dust in the air by the lightning discharge at the pointed rod. In such a case a
^:— iiN— ^
Belgian Academy of Science.
12
NITROKXPLOSIVES.
fork or aigrette of five or more points should invariably be used in place of a single point.
In Fig. 4 {a and b) is shown the Government method for protecting buildings in which explosives are made or
Fig. 4a. — Government System of Lightning Conductors for Large Buildings.
stored. Multiple points or aigrettes would be better. Lord Kelvin and Professor Melsens favour points, and it is generally admitted that lightning does not strike buildings at a single point, but rather in a sheet ; hence, in such
Fig. \b. — Government System of Lightning Conductors for Small Buildings.
cases, or in the event of the globular form being assumed by the lightning, the aigrette will constitute a much more effective protection than a single point. As to the spacing of conductors, they may, even on the most important build-
SYSTEMS OF PROTECTION. 1 3
ings, be spaced at intervals of 50 feet. There will then be no point on the building more than 25 feet from the con- ductor. This " 2 5 -feet rule " can be adhered to with advantage in all overground buildings for explosives.
Underground magazines should, whenever possible, also be protected, because, although less exposed than overground buildings, they frequently contain explosives packed in metal cases, and hence would present a line of smaller electrical resistance than the surrounding earth would offer to the lightning. The conductor should be arranged on the same system as for overground build- ings, but be applied to the surface of the ground over the magazines.
In all situations where several conductors are joined in one system, the vertical conductors should be con- nected both at the top and near the ground line. The angles and the prominent portions of a building being the most liable to be struck, the conductors should be carried over and along these projections, and therefore along the ridges of the roof. The conductors should be connected to any outside metal on the roofs and walls, and specially to the foot of rain-water pipes.
All the lightning conductors should be periodical!}* tested, to see that they are in working condition, at least every three months, according to Mr Richard Anderson. The object of the test is to determine the resistance of the earth-connection, and to localise any defective joints or parts in the conductors. The best system of testing the conductors is to balance the resistance of each of the earths against the remainder of the system, from which the state of the earths ma)- be inferred with sufficient accuracy for all practical purposes.
Captain Bucknill, R.E., has designed an instrument to test resistance which is based on the Post Office pattern resistance coil, and is capable of testing to approximate accuracy up to 200 ohms, and to measure roughly up to 2,000 ohms. Mr R. Anderson's apparatus
14 NITRO-EXPLOSIVES.
is also very handy, consisting of a case containing three Leclanche cells, and a galvanometer with a " tangent " scale and certain standard resistances. Some useful articles on the protection of buildings from lightning will be found in Arms and Explosives, July, August, and September 1892, and by Mr Anderson, Brit. Assoc, 1878-80.
Nitro-Glycerine. — One of the most powerful of modern explosive agents is nitro-glycerine. It is the explosive contained in dynamite, and forms the greater part of the various forms of blasting gelatines, such as gelatine dyna- mite and gelignite, both of which substances consist of a mixture of gun-cotton dissolved in nitro-glycerine, with the addition of varying proportions of wood-pulp and salt- petre, the latter substances acting as absorbing materials for the viscid gelatine. Nitro-glycerine is also largely used in the manufacture of smokeless powders, such as cordite, ballistite, and several others.
Nitro-glycerol, or glycerol tri-nitrate, was discovered by Sobrero in the year 1847. In a letter written to M. Pelouse, he says, " when glycerol is poured into a mixture of sulphuric acid of a specific gravity of 1.84, and of nitric acid of a gravity of 1.5, which has been cooled by a freezing mixture, that an oily liquid is formed." This liquid is nitro-glycerol, or nitro-glycerine, which for some years found no important use in the arts, until the year 1863, when Alfred Nobel first started a factory in Stockholm for its manufacture upon a large scale ; but on account of some serious accidents taking place, its use did not become general.
It was not until Nobel conceived the idea (in 1866) of absorbing the liquid in some absorbent earth, and thus forming the material that is now known as dyna- mite, that the use of nitro-glycerine as an explosive became general.
Among those who improved the manufacture of
NITROGLYCERINE. 1 5
nitroglycerine was Mowbray, who, by using pure gly- cerine and nitric acid free from nitrous acid, made very great advances in the manufacture. Mowbray was pro- bably the first to use compressed air for the purpose of keeping the liquids well agitated during the process of nitration, which he conducted in earthenware pots, each containing a charge of 17 lbs. of the mixed acids and 2 lbs. of glycerol.
A few years later (1872), MM. Boutnny and Faucher, of Vonges,* proposed to prepare nitro-glycerine by mix- ing the sulphuric acid with the glycerine, thus forming a sulpho-glyceric acid, which was afterwards mixed with a mixture of nitric and sulphuric acids. They claimed for this method of procedure that the final temperature is much lower. The two mixtures are mixed in the pro- portions— Glycerine, 100 ; nitric acid, 2S0 ; and sulphuric acid, 600. They state that the rise of temperature upon mixing is limited from io° to 15" C. ; but this method requires a period of twenty-four hours to complete the nitration, which, considering the danger of keeping the nitro-glycerine in contact with the mixed acids for so long, probably more than compensates for the somewhat doubtful advantage of being able to perform the nitra- tion at such a low temperature. The Boutnny process was in operation for some time at Pembrey Burrows in Wales, but after a serious explosion the process was abandoned.
Nitro-glycerine is now generally made by adding the glycerine to a mixture of sulphuric and nitric acids. The sulphuric acid, however, takes no part in the reaction, but is absolutely necessary to combine with the water that is formed by the decomposition, and thus to keep up the strength of the nitric acid, otherwise lower nitrates of glycerine would be formed that are soluble in water, and
* Comptes Rendus, 75 ; and Desortiaux, "Traite sur la Poudre," 684-686.
1 6 NITRO-EXPLOSIVES.
which would be lost in the subsequent process of washing to which the nitrocompound is subjected, in order to remove the excess of acids, the retention of which in the nitro-glycerol is very dangerous. Nitro-glycerol, which was formerly considered to be a nitro-substitution com- pound of glycerol, was thought to be formed thus — C8H8Os+ 3HNOs=CsH6(N02)808+3H20 ; but more recent researches rather point to its being re- garded as a nitric ether of glycerol, or glycerine, and to its being formed thus —
C3HsOs+ 3HNOs = C3H.(N03)o + 3H20. 92 227
[OH The formula of glycerine is C3H803, or C3H5 J OH
[oh
( ONO,
and that of the mono-nitrate of glycerine, C3H5 ] OH
" [ OH ( ON02 and of the tri-nitrate or (nitro-glycerine), C3H5 -l ONO.,
" [ ON02 that is, the three hydrogens of the semi-molecules of hydroxyl in the glycerine have been replaced by the N02 group.
In the manufacture upon the large scale, a mixture of three parts by weight of nitric acid and five parts of sulphuric acid are used. From the above equation it will be seen that every 1 lb. of glycerol should give
/227 4" I \
2.47 lbs. of nitro-glycerol ( — = 2.47 J, but in practice
the yield is only about 2 lbs. to 2.22, the loss being accounted for by the unavoidable formation of some of the lower nitrate, which dissolves in water, and is thus washed away, and partly perhaps to the presence of a little water (or other non-nitrable matter) in the glycerine, but chiefly to the former, which is due to the acids having become too weak.
CHAPTER II. MA NUFA CT UR E OF NI TR 0- GL 1 rCERINE.
Properties of Nitro-Glycerine — Manufacture of Nitro-Glycerine — Nitration — The Nathan Nitrator — Separation — Filtering and Washing — The Waste Acids — Treatment of the Waste Acid from the Manufacture of Nitro- Glycerine and Gun-Cotton.
Properties of Nitro - Glycerine. — Nitro-glycerol is a heavy oily liquid of specific gravity 1.6 at 15' C, and when quite pure is colourless. The commercial product is a pale straw yellow, but varies much according to the purity of the materials used in its manufacture. It is insoluble in water, crystallises at 10.50 C, but different com- mercial samples behave very differently in this respect, and minute impurities prevent or delay crystallisation. Solid nitro-glycerol* melts at about 12" C, but requires to be exposed to this temperature for some time before melting. The specific gravity of the solid form is 1.735 at +10" C. ; it contracts one-twelfth of its volume in solidifying. Beckerheimf gives the specific heat as 0.4248 between the temperatures of 9.50 and 9.8° C, and L. de Bruyn gives the boiling point as above 200 .
Nitro-glycerine has a sweet taste, and causes great depression and vertigo. It is soluble in ether, chloro- form, benzene, glacial acetic acid, and nitro-benzene, in 1.75 part of methylated spirit, very nearly insoluble in water, and practically insoluble in carbon bisulphide. Its formula is C3H5(N03)3, and molecular weight 227.
* Di-nitro-mono chlorhydrin, when added to nitro-glycerine up to 20 per cent., is said to prevent its freezing, t Isb., Chcm. Tech., 22, 481-487. 1876.
B
1 8 NITKO-EXPLOSIVES.
When pure, it may be kept any length of time without decomposition. Berthelot kept a sample for ten years, and Mr G. M'Roberts, of the Ardeer Factory, for nine years, without their showing signs of decomposition ; but if it should contain the smallest trace of free acid, decom- position is certain to be started before long. This will generally show itself by the formation of little green spots in the gelatine compounds, or a green ring upon the sur- face of liquid nitro-glycerine. Sunlight will often cause it to explode ; in fact, a bucket containing some water that had been used to wash nitro-glycerine, and had been left standing in the sun, has in our experience been known to explode with considerable force. Nitro-glycerine when pure is quite stable at ordinary temperatures, and samples have been kept for years without any trace of decomposition. It is very susceptible to heat, and even when quite pure will not stand a temperature of ioo° C. for a longer period than a few hours, without undergoing decomposition. Up to a temperature of 45° C, however, properly made and purified nitro-glycerine will remain unchanged almost indefinitely. The percentage composition of nitro- glycerine is as follows : —
Found. Theory for C3H,(N03)3. Carbon - ' - - - 15.62 15.86 per cent.
Hydrogen - - - 2.40 2.20 „
Nitrogen - - - 17.90 18.50 ,,
Oxygen - - - - ... 63.44
The above analysis is by Beckerheim. Sauer and Adou give the nitrogen as 18.35 to 10.54 Per cent, by Dumas' method ; but I have never found any difficulty in obtain- ing percentages as high as 18.46 by the use of Lunge's nitrometer. The decomposition products by explosion are shown by the following equation —
2C3H5(N03)3 = 6C02+5H,0-r-6N + 0;
that is, it contains an excess of 3.52 per cent, of oxygen above that required for complete combustion ; 100 grms. would be converted into —
PROPERTIES OF XITRO-GLYCERINE. 1 9
Carbonic Acid (CO). 58.15 per cent. Water - - - 19.83 ,,
Oxygen - - 3.52 per cent. Nitrogen - - 18.50 ,,
|
NO - |
48.2 per cent. |
H |
|
CO - |
35-9 |
N |
|
C02 - |
12.7 |
CH4 |
The volume of gases produced at o'J and 760 mm., calculated from the above, is 714 litres per kilo, the water being taken as gaseous. Nitro-glycerine is decomposed differently if it is ignited as dynamite {i.e., kieselguhr dynamite;, and if the gases are allowed to escape freely under a pressure nearly equal to that of the atmosphere. Sarrau and Vieille obtained under these conditions, for 100 volumes of gas —
1.6 per cent.
o-3
These conditions are similar to those under which a mining"
o
charge, simply ignited by the cap, burns away slowly under a low pressure (i.e., a miss fire). In a recent communica- tion, P. F. Chalon (Engineering and Mining Journal, 1892) says, that in practice nitro-glycerine vapour, carbon mon- oxide, and nitrous oxide, are also produced as the result of detonation, but he attributes their formation to the use of a too feeble detonator.
Nitro-glycerine explodes very violently by concussion. It may be burned in an open vessel, but if heated above 250° C. it explodes. Professor C. E. Munroe gives the firing point as 203^-205° C, and L. de Bruyn* states its boiling point as 185°. He used the apparatus devised by Horsley. The heat of formation of nitro-glycerine, as deduced from the heat of combustion by M. Longuinine, is 432 calories for 1 grm. ; and the heat of combustion equals 1,576 cals. for 1 grm. In the case of nitro-glycerine the heat of total combustion and the heat of complete decomposition are interchangeable terms, since it contains an excess of oxygen. According to Dr W. H. Perkin, F.R.S.,f the magnetic rotation of nitro-gylcerine is 5,407,
* Jour. Soc. Client. Ind., June 1S96, p. 471. t Jour. Chan. Soc., W. H. Perkin, 18S9, p. 726.
20
NITRO-EXPLOSIVES.
and that of tri-methylene nitrate, 4.769 (diff. = .638). Dr Perkin says : " Had nitre-glycerine contained its nitrogen in any other combination with oxygen than as — O — NO.,, as it might if its constitution had been represented as C3H2(N0.2)3(OH)3, the rotation when compared with propyl nitrate (4.085) would be abnormal."
The solubility of nitro-glycerine in various solvents has been investigated by A. H. Elliot ; his results may be summarised as follows : —
|
Solvent. |
Cold. |
Warm. |
|
Water |
Insoluble - |
Slightly soluble. |
|
Alcohol, absolute |
Soluble |
Soluble. |
|
93%" |
11 |
j> |
|
» 80%- |
Slowly soluble |
>) |
|
» 5o%- |
Insoluble - |
Slightly soluble. |
|
Methyl alcohol |
Soluble |
Soluble. |
|
Amyl |
)> |
)> |
|
Ether, ethylic - |
■>■> |
,, |
|
,, acetic - |
>> |
11 |
|
Chloroform |
>> |
>> |
|
Acetone - |
?> |
j> |
|
Sulphuric acid (1.845) |
)) |
>! |
|
Nitric acid (1.400) - |
Slowly soluble |
1) |
|
Hydrochloric acid (1.200) |
Insoluble, decom- posed |
Slowly soluble. |
|
Acetic acid, glacial - |
Soluble |
Soluble. |
|
Carbolic acid - |
" |
J5 |
|
Astral oil |
Insoluble - |
Insoluble. |
|
Olive ,, |
Soluble |
Soluble. |
|
Stearine oil |
)! |
)> |
|
Mineral jelly - |
Insoluble - |
Insoluble. |
|
Glycerine |
>) |
,, |
|
Benzene - |
Soluble |
Soluble. |
|
Nitro-benzene - |
)> |
>) |
|
Toluene - |
>) |
j) |
|
Carbon bi-sulphide - |
Insoluble |
Slightly affected. |
|
Turpentine |
j> |
Soluble. |
|
Petroleum naphtha, 71" - |
5) |
Insoluble. |
|
76° B. |
PROPERTIES OF XITRO-GLVCERINE.
21
|
Solvent. |
Cold. |
Warm. |
|
Caustic soda (i : 10 solu- |
Insoluble - |
Insoluble. |
|
tion) Borax, 5 % solution - Ammonia (.980) Ammonium sulph-hydrate |
Insoluble, sulphur |
slightly affected. Decomposed. |
|
Iron sulphate solution Iron chloride (1.4 grm. Fe to 10 c.c. NoO) Tin chloride - |
separates Slightly affected - Slowly affected - Slightly affected - |
Affected. Decomposed. Affected. |
Many attempts have been made to prepare nitro- glycerine explosives capable of withstanding comparatively low temperatures without freezing, but no satisfactory solu- tion of the problem has been found. Among the substances that have been proposed and used with more or less success, are nitro-benzene, nitro-toluene, di-nitro-mono-chlorhydrine, solid nitro derivatives of toluene,* are stated to lower the freezing point of nitro-glycerine to — 20' C. without alter- ing its sensitiveness and stability. The subject has been investigated by S. Nauckhoff,+ who states that nitro- glycerine can be cooled to temperatures (—40"' to —50' C.) much below its true freezing point, without solidifying, by the addition of various substances. When cooled by means of a mixture of solid carbon, dioxide, and ether, it sets to a glass)7 mass, without any perceptible crystallisation. The mass when warmed to o' C. first rapidly liquefies and then begins to crystallise. The true freezing point of pure nitro-glycerine was found to be 12.30 C. The technical product, owing to the presence of di-nitro-glycerine, freezes at io.5J C. According to Raoult's law, the lowering of
* Eng. Pat. 25,797, November 1904. t Z. Angew. Chem., 1905, iS, 11-22, 53-60.
22 NITRO-EXPLOSIVES.
the freezing point caused by m grms. of a substance with
the molecular weight M, when dissolved in ioo grms. of
m the solvent, is expressed by the formula: A = E^, where
E is a constant characteristic for the solvent in question. The value of E for 'nitro-glycerine was found to be 70.5 when calculated, according to Van 't Hoff's formula, from the melting point and the latent heat of fusion of the substance. Determinations of the lowering of the freezing point of nitro-glycerine by additions of benzene, nitro- benzene, di-nitro-benzene, tri-nitro-benzene, p.-nitro-toluene, o.-nitro-toluene,di-nitro-toluene, naphthalene, nitro-naphtha- lene, di-nitro-naphthalene, ethyl acetate, ethyl nitrate, and methyl alcohol, gave results agreeing fairly well with Raoult's formula, except in the case of methyl alcohol, for which the calculated lowering of the freezing point was greater than that observed, probably owing to the formation of complex molecules in the solution. The results show that, in general, the capacity of a substance to lower the freezing point of nitro-glycerine depends, not upon its freezing point, or its chemical composition or constitution, but upon its molecular weight. Nauckhoff states that a suitable substance for dissolving in nitro-glycerine, in order to lower the freezing point of the latter, must have a relatively low molecular weight, must not appreciably diminish the explosive power and stability of the explosive, and must not be easily volatile at relatively high atmospheric temperatures ; it should, if possible, be a solvent of nitro-cellulose, and in every case must not have a prejudicial influence on the gelatinisation of the nitro-cellulose.
Manufacture of Nitro-Glycerine. — Nitro-glycerine is prepared upon the manufacturing scale by gradually adding glycerine to a mixture of nitric and sulphuric acids of great strength. The mixed acids are contained in a lead vessel, which is kept cool by a stream of water continually passing through worms in the interior of the nitrating vessel, and
NITRATION OF GLYCERINE. 23
the glycerine is gradually added in the form of a fine stream from above. The manufacture can be divided into three distinct operations, viz., nitration, separation, and washing, and it will be well to describe these operations in the above order.
Nitration. — The most essential condition of nitrating is the correct composition and strength of the mixed acids. The best proportions have been found to be three parts by weight of nitric acid of a specific gravity 1.525 to 1.5 30, and containing as small a portion of the oxides of nitrogen as possible, to five parts by weight of sulphuric acid of a specific gravity of 1.840 at 15° C, and about 97 per cent, of mono-hydrate. It is of the very greatest importance that the nitric acid should be as strong as possible. Nothing under a gravity of 1.52 should ever be used even to mix with stronger acid, and the nitration will be proportional to the strength of the acid used, provided the sulphuric acid is also strong enough. It is also of great importance that the oxides of nitrogen should be low, and that they should be kept down to as low as 1 per cent., or even lower. It is also very desirable that the nitric acid should contain as little chlorine as possible. The following is the analysis of a sample of nitric acid, which gave very good results upon the commercial scale: — Specific gravity, 1.525, N204, 1.03 per cent. ; nitric acid (HN03), 95.58 per cent.
The amount of real nitric acid (mono-hydrate) and the amount of nitric peroxide present in any sample should always be determined before it is used for nitrating purposes. The specific gravity is not a sufficient guide to the strength of the acid, as an acid having a high gravity, due to some 3 or 4 per cent, of nitric oxides in solution, will give very poor nitration results. A tenth normal solution of sodium hydroxide (NaOH), with phenol- phthalein as indicator, will be found the most convenient method of determining the total acid present. The follow- ing method will be found to be very rapid and reliable : — ■
24 NITRO-EXPLOSIVES.
Weigh a ioo c.c. flask, containing a few cubic centimetres of distilled water, and then add from a pipette I c.c. of the nitric acid to be examined, and reweigh (this gives the weight of acid taken). Now make up to ioo c.c. at 150 C. ; shake well, and take out 10 c.c. with a pipette ; drain into a small Erlenmeyer flask, and add a little of the phenol- phthalein solution, and titrate with the tenth normal soda solution.
The nitric peroxide can be determined with a solu-
N tion of potassium permanganate of — strength, thus :
Take a small conical flask, containing about 10 c.c. of water, and add from a burette 10 to 16 c.c. of the permanganate solution ; then add 2 c.c. of the acid to be tested, and shake gently, and continue to add permanganate solution as long as it is decolourised, and until a faint pink colour is permanent.
N Example. permanganate 3.16 grms. per litre, I c.c.
= 0.0046 grm. N204, 2 c.c. of sample of acid specific gravity 1.52 = 3.04 grms. taken for analysis. Took 20 c.c. perman-
1 4.- * xt r\ a 092 X IOO
cranate solution, 0.0046 x 20 = . 092 n'm, JN0(J,, and — -
t, » t * & 2 4> 2.04
= 3.02 per cent. N004. The specific gravity should be taken with an hydrometer that gives the specific gravity directly, or, if preferred, the 2 c.c. of acid may be weighed.
A very good method of rapidly determining the strength of the sulphuric acid is as follows : — Weigh out in a small weighing bottle, as nearly as possible, 2.45 grms. This is best done by running in 1.33 c.c. of the acid (1.33x1.84 = 2.447). Wash into a large Erlenmeyer flask, carefully washing out the bottle, and also the stopper, &c. Add a drop of phenol-phthalein solution and titrate, with a half normal solution of sodium hydrate (use a 100 c.c. burette). Then if 2.45 grms. exactly have been taken, the readings on the burette will equal percentages of H0S04 (mono-hydrate)
MIXING ACIDS FOR NITRATION. 25
if not, calculate thus : — 2.444 grnis. weighed, required 95.4 c.c. NaOH. Then—
2.444 : 95-4 : : 2-45 : -t' = 95.64 per cent. H2S04.
It has been proposed to free nitric acid from the oxides of nitrogen by blowing compressed air through it, and thus driving the gases in solution out. The acid was contained in a closed lead tank, from which the escaping fumes were conducted into the chimney shaft, and on the bottom of which was a lead pipe, bent in the form of a circle, and pierced with holes, through which the compressed air was made to pass ; but the process was not found to be of a very satisfactory nature, and it is certainly better not to allow the formation of these compounds in the manufacture of the acid in the first instance. Another plan, however, is to heat the acid gently, and thus drive out the nitrous gases. Both processes involve loss of nitric acid.
Having obtained nitric and sulphuric acids as pure as possible, the next operation is to mix them. This is best done by weighing the carboys in which the acids are generally stored before the acids are drawn off into them from the condensers, and keeping their weights constantly attached to them by means of a label. It is then a simple matter to weigh off as many carboys of acid as ma)- be required for any number of mixings, and subtract the weights of the carboys. The two acids should, after being weighed, be poured into a tank and mixed, and subsequently allowed to flow into an acid egg or montjus, to be after- wards forced up to the nitrating house in the danger area. The montjus or acid egg is a strong cast-iron tank, of either an egg shape, or a cylinder with a round end. If of the former shape, it would lie on its side, and upon the surface of the ground, and would have a manhole at one end, upon which a lid would be strongly bolted down ; but if of the latter shape, the lid, of course, is upon the top, and the montjus itself is let into the ground. In either case, the principle is the same. One pipe, made of stout lead, goes
26 NITRO-EXPLOSIVES.
to the bottom, and another just inside to convey the com- pressed air, the acids flowing' away as the pressure is put on, just as blowing down one tube of an ordinary wash-bottle forces the water up the other tube to the jet. The pressure necessarily will, of course, vary immensely, and will depend upon the height to which the acid has to be raised and the distance to be traversed.
The mixed acids having been forced up to the danger area, and to a level higher than the position of the nitrating house, should, before being used, be allowed to cool, and leaden tanks of sufficient capacity to hold at least enough acid for four or five nitrations should be placed in a wooden house upon a level at least 6 or 7 feet above the nitrating house. In this house also should be a smaller lead tank, holding, when filled to a certain mark, just enough of the mixed acids for one nitration. The object of this tank is, that as soon as the man in charge knows that the last nitration is finished, he refills this smaller tank (which contains just enough of the mixed acids), and allows its contents to flow down into the nitrating house and into the nitrator, ready for the next nitration. The nitration is usually conducted in a vessel constructed of lead, some 4 feet wide at the bottom, and rather less at the top, and about 4 feet or so high. The size, of course,' depends upon the volume of the charge it is intended to nitrate at one operation, but it is always better that the tank should be only two-thirds full. A good charge is 16 cwt. of the mixed acids, in the proportion of three to five ; that is, 6 cwt. of nitric acid, and 10 cwt. of sulphuric acid, and 247 lbs. of glycerine.
Upon reference to the equation showing the formation of nitro-glycerine, it will be seen that for every 1 lb. of glycerine 2.47 lbs. of nitro-glycerine should be furnished,* but in practice the yield is only a little over 2 lbs., the
227 x 1 * Thus if 92 lbs. glycerine give 227 lbs. nitro-glycerine,
= 2.47 lbs.
CONSTRUCTION OF NITRATOR.
27
loss being accounted for by the unavoidable formation of some of the lower nitrate of glycerine (the mono-nitrate), which afterward dissolves in the washing waters. The lead tank (Fig. 5) is generally cased in woodwork, with a platform in front for the man in charge of the nitrating to stand upon, and whence to work the various taps. The top of the tank is closed in with a dome of lead, in which is a small glass window, through which the progress of the nitrating operation can be watched. From the top of this
Fig. 5. — Toi' of Nitrator. A, Fume Pipe; B, Water Pipes for Cooling; C, Acid Mixture Pipe; E, Compressed Air; G, Glycerine Pipe and Funnel; T, Thermometer; II'. Window.
dome is a tube of lead which is carried up through the roof of the building. It serves as a chimney to carry off the acid fumes which are given off during the nitration. The interior of this tank contains at least three concentric spirals of at least i-inch lead pipe, through which water can be made to flow during the whole operation of nitrating. Another lead pipe is carried through the dome of the tank, as far as the bottom, where it is bent round in the form of
28 NITRO-EXPLOSIVES.
a circle. Through this pipe, which is pierced with small holes, about I inch apart, compressed air is forced at a pressure of about 60 lbs. in order to keep the liquids in a state of constant agitation during the whole period of nitration. There must also be a rather wide pipe, of say 2 inches internal diameter, carried through the dome of the tank, which will serve to carry the mixed acid to be used in the operation into the tank. There is still another pipe to go through the dome, viz., one to carry the glycerine into the tank. This need not be a large bore pipe, as the glycerine is generally added to the mixed acids in a thin stream (an injector is often used).
Before the apparatus is ready for use, it requires to have two thermometers fixed, one long one to reach to the bottom of the tank, and one short one just long enough to dip under the surface of the acids. When the tank contains its charge, the former gives the tempera- ture of the bottom, and the latter of the top of the mixture. The glycerine should be contained in a small cistern, fixed in some convenient spot upon the wall of the nitrating house, and should have a pipe let in flush with the bottom, and going through the dome of the nitrating apparatus. It must of course be provided with a tap or stop-cock, which should be placed just above the point where the pipe goes through the lead dome.
Some method of measuring the quantity of glycerine used must be adopted. A gauge-tube graduated in inches is a very good plan, but it is essential that the graduations should be clearly visible to the operator upon the platform in front of the apparatus. A large tap made of earthenware (and covered with lead) is fixed in the side of the nitrating tank just above the bottom, to run off the charge after nitration. This should be so arranged that the charge may be at option run down the conduit to the next house or discharged into a drowning tank, which may sometimes be necessary in cases of decomposition. The drowning tank is generally
POINTS IN NITRATION. 2Q.
some 3 or 4 yards long and several feet deep, lined with cement, and placed close outside the building.
The apparatus having received a charge of mixed acids, the water is started running through the pipes coiled inside the tank, and a slight pressure of com- pressed air is turned on,* to mix the acids up well before starting. The nitration should not be commenced until the two thermometers register a temperature of 180 C. The glycerine tap is then partially opened, and the glycerine slowly admitted, and the compressed air turned on full, until the contents of the apparatus are in a state of very brisk agitation. A pressure of about 40 lbs. is about the minimum (if 247 lbs. of glycerine and 16 cwt. of acids are in the tank;. If the glycerine tube is fitted with an injector, it may be turned on almost at once. The nitration will take about thirty minutes to complete, but the compressed air and water should be kept on for an additional ten minutes after this, to give time for all the glycerine to nitrate. The temperature should be kept as low as possible (not above 18' C).
The chief points to attend to during the progress of the nitration are —
1. The temperature registered by the two ther- mometers.
2. The colour of the nitrous fumes given off (as seen through the little window in the dome of the apparatus^.
3. The pressure of the compressed air as seen from a gauge fixed upon the air pipe just before it enters the apparatus.
4. The gauge showing the quantity of glycerine used. The temperature, as shown by either of the two ther- mometers, should not be at any time higher than 25 J C.
* At the Halton Factory, Germany, cylinders of compressed carbon dioxide are connected with the air pipes so that in the event of a failure of the air supply the stirring can be continued with this gas if necessary.
30 NITRO-EXPLOSIVES.
If it rises much above this point, the glycerine should be at once shut off, and the pressure of air increased for some few minutes until the temperature falls, and no more red fumes are given off.
The nitration being finished, the large earthenware tap at the bottom of the tank is opened, and the charge allowed to flow away down the conduit to the next building, i.e., to the separator.
The nitrating house is best built of wood, and should have a close-boarded floor, which should be kept scrupu- lously clean, and free from grit and sand. A wooden pail and a sponge should be. kept in the house in order that the workman may at once clean up any mess that may be made, and a small broom should be handy, in order that any sand, &c, may be at once removed. It is a good plan for the nitrator to keep a book in which he records the time of starting each nitration, the temperature at starting and at the finish, the time occupied, and the date and number of the charge, as this enables the foreman of the danger area at any time to see how many charges have been nitrated, and gives him other useful information conducive to safe working. Edward Liebert has devised an improvement in the treatment of nitro-glycerine. He adds ammonium sul- phate or ammonium nitrate to the mixed acids during the operation of nitrating, which he claims destroys the. nitrous acid formed according to the equation —
(NH,)2S04+2HN03 = H2S04+2N2+4H20.
I am not aware that this modification of the process of nitration is in use at the present time.
The newly made charge of nitro-glycerine, upon leaving the nitrating house, flows away down the con- duit, either made of rubber pipes, or better still, of woodwork, lined with lead and covered with lids made of wood (in short lengths), in order that by lifting them at any point the condition of the conduit can be ex-
POSITION OF THE NITRATOR.
amined, as this is of the greatest importance, and the conduit requires to be frequently washed out and the sulphate of lead removed. This sulphate always con- tains nitro-glycerine, and should therefore be burnt in some spot far removed from any danger building or magazine, as it frequently explodes with considerable violence.
In works wrhere the manufacture of nitro-glycerine is of secondary importance, and some explosive containing only perhaps 10 per cent, of nitro- glycerine is manufactured, and where 50 or 100 lbs. of glycerine are nitrated at one time, a very much smaller nitrating apparatus than the one that has been already described will be probably all that is required. In this case the form of apparatus shown in Fig. 6 will be found very satisfactory. It should be made of stout lead (all lead used for tanks, &c, must be "chemical lead"), and may be made to hold 50 or 100 lbs. as found most convenient. This nitrator can very well be placed in the same house as the separator ; in fact, where such a small quantity of nitro-glycerine is re- quired, the whole series of operations, nitrating, separation, and washing, &c, may very well be performed in the same building. It will of course be necessary to place the nitrator on a higher level than the separator, but this can easily be done by having platforms of different heights, the nitration being performed upon the highest. The con- struction of this nitrator is essentially the same as in the larger one, the shape only being somewhat different. Two water coils will probably be enough, and one thermometer. It will not be necessary to cover this form in with wood- work.
Fig. 6. — Small Nit ;atoe. AT, Tap for Discharging ; P, Water Pipes; T, Ther- mometer ; W, Windows ; P', Glycerine Pipe.
32 NITRO-EXPLOSIVES.
The Nathan Nitrator.* — This nitrator is the patent of Lt.-Col. F. L. Nathan and Messrs J. M. Thomson and W. Rintoul of Waltham Abbey, and will probably before long entirely supersede all the other forms of nitrator on account of its efficiency and economy of working. With this nitrator it is possible to obtain from 2.21 to 2.22 parts of nitro-glycerine from every 1 part of glycerine. The apparatus is so arranged that the nitration of the glycerine, the separation of nitro-glycerine produced, as well as the operation of "after-separation," are carried out in one vessel. The usual nitrating vessel is provided with an acid inlet pipe at the bottom, and a glass separation cylinder with a lateral exit or overflow pipe at the top. This cylinder is covered by a glass hood or bell jar during nitration to direct the escaping air and fumes into a fume pipe where the flow of the latter may be assisted by an air injector. The lateral pipe in the separation cylinder is in connection with a funnel leading to the prewash tank. The drawing (Fig. 7) shows a vertical section of the apparatus ; a is the nitrating vessel of usual construction, having at the bottom an acid inlet pipe with three branches, one leading to the de-nitrating plant, c leading to the drowning tank, and d, which extends upwards and has two branches, e leading to the nitrating acids tank, and/" to the waste acid tank. On the sloped bottom of the nitrating vessel a lies a coil ^r of perforated pipe for blowing air, and there are in the vessel several coils //, three shown in the drawing, for circulation of cooling water. At the top of the vessel there is a glass cylinder i, having a lateral outlet j directed into the funnel mouth of a pipe k leading to the prewash tank. Over the cylinder i is a glass globe /, into which opens a pipe m for leading off fumes which may be promoted by a compressed air jet from a pipe r oper- ating as an injector. Into an opening of the glass dome / is inserted a vessel n, which is connected by a flexible
* Eng. Pat. 15,983, August 1901.
THE NATHAN NlTRATOR. 33
pipe p to the glycerine tank, and from the bottom of n, which is perforated and covered with a disc perforated with holes registering with those through the bottom, this
Fig. 7. — Nathan's Nitrator for Nitro-Glycerine. (a) Nitrating Vessel ; (b) to Separating Vessel ; (c) to Drowning Tank ; (c ) Nitrating Acids enter {/) to the Waste Acids ; (g) Coils for Compressed Air ; (h) Pipes for Cooling Water ; (£) Glass Cylinder ; (_/) Outlet to k ; (k) leading to Prewash Tank ; (/) Glass Dome ; (m) Pipe to lead off for Escape of Fumes ; («) Vessel ; (/) Pipe conveying Glycerine ; (q) Knob to turn off Glycerine ; (r) Compressed Air Jet ; (s) Thermometer.
disc being connected by a stem with a knob q by which it can be turned so as to throttle or cut off passage of glycerine through the bottom. s is a thermometer for indicating the temperature of the contents of the vessel. In operating with this apparatus the nitrating acid is
C
34 NITRO-EXPLOSlVES.
introduced into the nitrating vessel by opening the cock of the pipe e. The glycerine is then run in by introducing n and opening the valve at its bottom, the contents of the vessel being agitated by air blown through the perforations of the pipe g. When the glycerine is all nitrated and the temperature has slightly fallen, the circulation of the water through the coils // and the air-stirring are stopped, and the glycerine supply vessel n is removed. The nitro- glycerine as it separates from the acids is raised by intro- ducing by the pipe f waste acid from a previous charge, this displacing the nitro-glycerine upwards and causing it to flow by the outlety and pipe k to the prewash tank. When nearly all the nitro-glycerine has been separated in this manner the acids in the apparatus may be run off by the pipe b to an after separating vessel for further settling, thus leaving the apparatus free for another nitra- tion, or the nitrating vessel itself may be used as an after separating bottle displacing the nitro-glycerine with waste acid as it rises to the top, or skimming off in the usual manner. When the separation of the nitro-glycerine is complete the waste acid is run off and denitrated as usual, a portion of it being reserved for the displacement of the nitro-glycerine in a subsequent operation.
In a further patent (Eng. Fat. 3,020, 1903; the authors propose with the object of preventing the formation and separation of nitro-glycerine in the waste acids, after the nitro-glycerine initially formed in the nitrating vessel has been separated and removed, to add a small quantity of water to the waste acids ; this is carried out as follows. A relatively small quantity of water is added, and this prevents all further separation of nitro-glycerine, and at the same time the strength of the waste acids is so slightly reduced that their separation and re-concentration are not affected. " After- separation " is thus done away with, and the nitro-glycerine plant simplified and its output increased. After nitration separation is commenced at a temperature such that when all the displacing acid has been added, and the separation
SEPARATION OF NITRO-GLYCERINE. 35
of the nitroglycerine is complete, the temperature of the contents of the nitrating vessel shall not be lower than 1 50 C. A sufficient quantity of the displacing acid is then run off through the waste-acid cock to allow of the remaining acids being air-stirred without splashing over the top. A small quantity of water, from 2 to 3 per cent, according to strength of acid ; if waste consists of sulphuric acid (mono- hydrate), 62 per cent. ; nitric acid (anhydrous), 33 per cent, and water 5 per cent. ; temperature 15° C, then 2 per cent, of water is added ; if waste acids contain less than 4 per cent, of water of temperature lower than 15° C, from 3 to 5 per cent, of water may have to be added. The water is added slowly through the separator cylinder, and the con- tents of the nitrator air-stirred, but not cooled, the tempera- ture being allowed to rise slowly and regularly as the water is added — usually about 3° C. for each per cent, of water added. When air-agitation has been stopped, the acids are kept at rest for a short time, in order to allow of any small quantity of initially formed nitro-glycerine adhering to the coils and sides of the vessel rising to the top. When this has been separated by displacement, the acids are ready for denitration, or can be safely stored without further precaution.
Separation. — The nitro - glycerine, together with the mixed acids, flows from the nitrating house to the separat- ing house, which must be on a lower level than the former. The separating house contains a large lead-lined tank, closed in at the top with a wooden lid, into which a lead pipe of large bore is fixed, and which is carried up through the roof of the building, and acts as a chimney to carry off any fumes. A little glass window should be fixed in this pipe in order that the colour of the escaping fumes may be seen. The conduit conveying the nitro-glyccrine enters the building close under the roof, and discharges its con- tents into the tank through the pipe G (Fig. 8). The tank is only about two-thirds filled by the charge. There is in
36
NITROEXPLOSIVES.
the side of the tank a small window of thick plate glass, which enables the workman to see the level of the charge, and also to observe the progress of the separation, which will take from thirty minutes to one hour.
The tank should be in connection with a drowning tank, as the charge sometimes gets very dangerous in this building. It must also be connected by a conduit with the filter house, and also to the secondary separator by another conduit. The tank should also be fitted with a compressed air pipe, bent in the form of a loop. It should lie upon the
Fig. 8. — Separator. A , Compressed Air Pipes ; G, Nitroglycerine enters from Nitrator ; IV, Nitro-glycerine to P ; L, Lantern Window ; \V, Window in Side ; S, Waste Acids to Secondary Separator ; T, Tap to remove last traces of Nitro-glycerine ; P, Lead Washing Tank ; A, Compressed Air; IV, Water Pipe ; N, Nitro-glycerine from Separator.
bottom of the vat. The object of this is to mix up the charge in case it should get too hot through decomposition. A thermometer should of course be fixed in the lid of the tank, and its bulb should reach down to the middle of the nitro-glycerine (which rests upon the surface of the mixed acids, the specific gravity of the nitro-glycerine being 1.6, and that of the waste acids 1.7 ; the composition of the acids is now 11 per cent. HN08, 6j per cent. H2S04, and 22 per cent, water), and the temperature carefully watched. If nothing unusual occurs, and it has not been necessary
FILTERING AND WASHING NITRO-GLYCERINE.
37
to bring the compressed air into use, and so disturb the process of separation, the waste acids ma)* be run away from beneath the nitro-glycerine, and allowed to flow away to the secondary separator, where any further quantity of nitro-glycerine that they contain separates out after rest- ing for some days. The nitro- glycerine itself is run into a smaller tank in the same house, where it is washed three or four times with its own bulk of water, containing about 3 lbs. of carbonate of soda to neutral- ise the remaining acid. This smaller tank should contain a lead pipe, pierced and coiled upon the bottom, through which compressed air may be passed, in order to stir up the charge with the water and soda. A fter this preliminary washing, the nitro-glycerine is drawn off into indiarubber buckets, and poured down the conduit to the filter house. The wash waters may be sent down a conduit to another building, in order to allow the small quantity of nitro-glycerine that has been retained in the water as minute globules to settle, if thought worth the trouble of saving. This, of course, will depend upon the usual out-turn of nitro-glycerine in a day, and the general scale of opera- tions.
Fig. 9. — Filtering and Washing Plant. IV, Lead Washing Tank ; WP, Water Pipe ; L, Lid ; S, Nitro- glycerine from Separator; A,B,C, Filtering Tanks; B2, Indiarubber Bucket.
Filtering and Washing. — The filter house (Fig. 9), which must of course be again on a somewhat lower level
38 NITRO-EXPLOSIVES.
than the separating house, must be a considerably larger building than either the nitrating or separating houses, as it is always necessary to be washing some five or six charges at the same time. Upon the arrival of the nitro- glycerine at this house, it first flows into a lead-lined wooden tank (w), containing a compressed air pipe, just like the one in the small tank in the separating house. This tank is half filled with water, and the compressed air is turned on from half to a quarter of an hour after the introduction of the charge. The water is then drawn off, and fresh water added. Four or five washings are gener- ally necessary. The nitro-glycerine is then run into the next tank (a), the top of which is on a level with the bottom of the first one. Across the top of this tank is stretched a frame of flannel, through which the nitro- glycerine has to filter. This removes any solid matters, such as dirt or scum. Upon leaving this tank, it passes through a similar flannel frame across another tank (b), and is finally drawn off by a tap in the bottom of the tank into rubber buckets. The taps in these tanks are best made of vulcanite.
At this stage, a sample should be taken to the labora- tory and tested. If the sample will not pass the tests, which is often the case, the charge must be rewashed for one hour, or some other time, according to the judgment of the chemist in charge. In the case of an obstinate charge, it is of much more avail to wash a large number of times with small quantities of water, and for a short time, than to use a lot of water and wash for half an hour. Plenty of compressed air should be used, as the compound nitric ethers which are formed are thus got rid of. As five or six charges are often in this house at one time, it is necessary to have as many tanks arranged in tiers, otherwise one or two refractory charges would stop the nitrating house and the rest of the nitro-glycerine plant. The chief causes of the washed material not passing the heat test are, either that the acids were not clean, or they contained objection-
TESTING NITROGLYCERINE. 39
able impurities, or more frequently, the quality of the glycerine used. The glycerine used for making nitro- glycerine should conform to the following tests, some of which, however, are of greater importance than others. The glycerine should —
i. Have minimum specific gravity at 15° C. of 1*261.
2. Should nitrify well.
3. Separation should be sharp within half an hour, without the separation of fiocculent matter, nor should any white fiocculent matter (due to fatty acids) be formed when the nitrated glycerine is thrown into water and neutralised with carbonate of soda.
4. Should be free from lime and chlorine, and contain only traces of arsenic, sulphuric acid, &c.
5. Should not leave more than 0.25 per cent, of in- organic and organic residue together when evaporated in a platinum dish without ebullition (about 160° C.) or partial decomposition.
6. Silver test fair.
7. The glycerine, when diluted one-half, should give no deposit or separation of fatty acids when nitric peroxide gas is passed through it. (Xos. 1, 2, 3, and 5 are the most essential.)
The white fiocculent matter sometimes formed is a very great nuisance, and any sample of glycerol which gives such a precipitate when tried in the laboratory should at once be rejected, as it will give no end of trouble in the separating house, and also in the filter house, and it will be very difficult indeed to make the nitro-glycerine pass the heat test. The out-turn of nitro-glycerine also will be very low. The trouble will show itself chiefly in the separating operation. Very often 2 or 3 inches will rise to the surface or hang about in the nitro-glycerine, and at the point of contact between it and the mixed acids, and will afterwards be very difficult to get rid of by filtration. The material appears to be partly an emulsion of the glycerine, and
40 NITRO-EXPLOSIVES.
partly due to fatty acids, and as there appears to be no
really satisfactory method of preventing its formation, or
of getting rid of it, the better plan is not to use any
glycerine for nitrating that has been found by experiment
upon the laboratory scale to give this objectionable matter.
One of the most useful methods of testing the glycerine,
other than nitrating, is to dilute the sample one-half with
water, and then to pass a current of nitric peroxide gas
through it, when a flocculent precipitate of elai'dic acid
(less soluble in glycerine than the original oleic acid) will
be formed. Nitrogen peroxide, N204, is best obtained by
heating dry lead nitrate (see Allen, " Commercial Organic
Analysis," vol. ii., 301).
When a sample of nitro-glycerine is brought to the
laboratory from the filter house, it should first be examined
to see that it is not acid.* A weak solution of Congo red
or methyl orange may be used. If it appears to be decidedly
alkaline, it should be poured into a separating funnel, and
shaken with a little distilled water. This should be repeated,
and the washings (about 400 c.c.) run into a beaker, a drop
of Congo red or methyl orange added, and a drop or so
N of — hydrochloric acid added, when it should give, with
two or three drops at most, a blue colour with the Congo red, or pink with the methyl orange, &c. The object of this test is to show that the nitro-glycerine is free from any excess of soda, i.e., that the soda has been properly washed out, otherwise the heat test will show the sample to be better than it is. The heat test must also be applied.
Upon leaving the filter house, where it has been washed and filtered, and has satisfactorily passed the heat test, it
* A. Leroux, Bui. Soc. CJiim. de Bel., xiw, August 1905, contends that experience does not warrant the assumption that free acid is a source of danger in nitro-glycerine or nitro-cellulose ; free alkali, he states, promotes their decomposition.
WASTE ACIDS. 4 1
is drawn off from the lowest tank in indiarubber buckets, and poured down the conduit leading to the precipitating house, where it is allowed to stand for a clay, or sometimes longer, in order to allow the little water it still contains to rise to the surface. In order to accomplish this, it is sufficient to allow it to stand in covered-in tanks of a conical form, and about 3 or 4 feet high. In many works it is previously filtered through common salt, which of course absorbs the last traces of water. It is then of a pale yellow colour, and should be quite clear, and can be drawn off by means of a tap (of vulcanite), fixed at the bottom of the tanks, into rubber buckets, and is ready for use in the preparation of dynamite, or any of the various forms of gelatine compounds, smokeless powders, &c, such as cordite, ballistite, and many others.
Mikolajezak {Chem. Zeit., 1904, Rep. 174) states that he has prepared mono- and di-nitro-glycerine, and believes that the latter compound will form a valuable basis for ex- plosives, as it is unfreezable. It is stated to be an odourless, unfreezable oil, less sensitive to percussion, friction, and increase of temperature, and to possess a greater solvent power for collodion-cotton than ordinary nitro-glycerine. It can thus be used for the preparation of explosives of high stability, which will maintain their plastic nature even in winter. The di-nitro-glycerine is a solvent for tri-nitro- glycerine, it can therefore be mixed with this substance, in the various gelatine explosives in order to lower the freezing point.
The Waste Acids. — The waste acids from the sepa- rating house, from which the nitro-glycerine has been as completely separated as possible, are run down the conduit to the secondary separator, in order to recover the last traces of nitro-glycerine that they contain. The composition of the waste acids is generally somewhat as follows : — Specific gravity, 1.7075 at 15° C. ; sulphuric acid, 67.2 per cent. ; nitric acid, 1 1.05 per cent. ; and water, 21.7 per cent.,
42 NITRO-EXPLOSIVES.
with perhaps as much as 2 per cent, of nitric oxide, and of course varying quantities of nitro-glycerine, which must be separated, as it is impossible to run this liquid away (unless it can be run into the sea) or to recover the acids by distillation as long as it contains this substance. The mixture, therefore, is generally run into large circular lead- lined tanks, covered in, and very much like the nitrating apparatus in construction, that is, they contain worms coiled round inside, to allow of water being run through to keep the mixture cool, and a compressed air pipe, in order to agitate the mixture if necessary. The top also should contain a window, in order to allow of the interior being seen, and should have a leaden chimney to carry off the fumes which may arise from decomposition. It is also useful to have a glass tube of 3 or 4 inches in diameter sub- stituted for about a foot of the lead chimney, in order that the man on duty can at any time see the colour of the fumes arising from the liquid. There should also be two thermo- meters, one long one reaching to the bottom of the tank, and one to just a few inches below the surface of the liquid.
The nitro-glycerine, of course, collects upon the surface, and can be drawn off by a tap placed at a convenient height for the purpose. The cover of the tank is generally conical, and is joined to a glass cylinder, which is cemented to the top of this lead cover, and also to the lead chimney. In this glass cylinder is a hole into which fits a ground glass stopper, through which the nitro-glycerine can be drawn off. There will probably never be more than an inch of nitro-glycerine at the most, and seldom that. It should be taken to the filter house and treated along with another charge. The acids themselves may either be run to waste, or better treated by some denitration plant. This house probably requires more attention than any other in the danger area, on account of the danger of the decomposition of the small quantities of nitro-glycerine, which, as it is mixed with such a large quantity of acids and water, is very
TREATMENT OF WASTE ACIDS. 43
apt to become hot, and decomposition, which sets up in spots where a little globule of nitro-glycerine is floating, surrounded by acids that gradually get hot, gives off nitrous fumes, and perhaps explodes, and thus causes the sudden explosion of the whole. The only way to prevent this is for the workman in charge to look at the thermometers frequently, and at the colour of the escaping fumes, and if he should notice a rise of temperature or any appearance of red fumes, to turn on the water and air, and stir up the mixture, when probably the temperature will suddenly fall, and the fumes cease to come off.
The cause of explosions in this building is either the non-attention of the workmen in charge, or the bursting of one of the water pipes, by which means, of course, the water, finding its way into the acids, causes a sudden rise of temperature. If the latter of these two causes should occur, the water should at once be shut off and the air turned on full, but if it is seen that an explosion is likely to occur, the tank should at once be emptied by allowing its contents to run away into a drowning tank placed close outside the house, which should be about 4 feet deep, and some 16 feet long by 6 feet wide ; in fact, large enough to hold a considerable quantity of water. But this last course should only be resorted to as a last extremity, as it is extremely troublesome to recover the small quantity of nitro-glycerine from the bottom of this tank, which is generally a bricked and cemented excavation some few yards from the house.
It has been proposed to treat these waste acids, con- taining nitro-glycerine, in Mr M. Prentice's nitric acid retort. In this case they would be run into the retort, together with nitrate of soda, in a fine stream, and the small quantity of nitro-glycerine, coming into contact with the hot mixture already in the retort, would probably be at once decomposed. This process, although not yet tried, promises to be a success. Several processes have been used for the denitration of these acids.
44 NITRO-EXPLOSIVES.
Treatment of the Waste Acid from the Manufacture of Nitro-Glycerine and Gun-Cotton. — The composition of these acids is as follows : —
Nitroglycerine and Gun-cotton Waste Acid. Sulphuric acid - 70 per cent. 78 per cent.
Nitric acid - - 10 „ 12 „
Water - - - - 20 „ 10 „
The waste acid from the manufacture of gun-cotton is generally used direct for the manufacture of nitric acid, as it contains a fairly large amount of sulphuric acid, and the small amount of nitro-cellulose which it also generally con- tains decomposes gradually and without explosion in the retort. Nitric acid may be first distilled off, the resulting sulphuric acid being then added to the equivalent amount of nitrate of soda. Nitric acid is then distilled over and condensed in the usual way. Very often, however, the waste acid is added direct to the charge of nitrate without previously eliminating the nitric acid. The treatment of the waste acid from the manufacture of nitro- glycerine is somewhat different. The small amount of nitro-glycerine in this acid must always be eliminated. This is effected either by allowing the waste acid to stand for at least twenty-four hours in a big vessel with a conical top, where all the nitro-glycerine which will have separated to the surface is removed by skimming ; or, better still, the "water- ing down process " of Col. Nathan may be employed. In Nathan's nitrator every existing trace of nitro-glycerine is separated from the acids in a few hours after the nitra- tion, and any further formation of nitro-glycerine is prevented by adding about 2 per cent, of water to the waste acids, which are kept agitated during the addition. The waste acid, now free from nitro-glycerine, but which may still contain organic matter, is denitrated by bringing it into contact with a jet of steam. The waste acid is passed in a small stream down through a tower of acid- resisting stoneware (volvic stone), which is closely packed
NITRIC ACID PLANT. 45
with earthenware, and at the bottom of which is the steam jet. Decomposition proceeds as the acid meets the steam, nitric and nitrous acids are disengaged and are passed out at the top of the tower through a pipe to a series of con- densers and towers, where the nitric acid is collected. The nitrous acid may be converted into nitric acid by introduc- ing a hot compressed air jet into the gases before they pass into the condensers. Weak sulphuric acid of sp. gr. 1.6 collects in a saucer in which the tower stands, and is then passed through a cooling worm. The weak sulphuric acid, now entirely free from nitric and nitrous acids, may be concentrated to sp. gr. 1.842 and 96 per cent. HoS04 by any of the well-known processes, e.g., Kessler, Webb, Benker, Delplace, &c, and it may be used again in the manufacture of nitro-glycerine or gun-cotton.
Two points in the manufacture of nitro-glycerine are of the greatest importance, viz., the purity of the glycerine used, and the strength and purity of the acids used in the nitration. With regard to the first of these, great care should be taken, and a complete analysis and thorough examination, including a preliminary experimental nitra- tion, should always be instituted. As regards the second, the sulphuric acid should not only be strong (96 per cent.), but as free from impurities as possible. With the nitric acid, which is generally made at the explosive works where it is used, care must be taken that it is as strong as possible (97 per cent, and up wards ). This can easily be obtained if the plant designed by Mr Oscar Guttmann * is used. Having worked Mr Guttmann's plant for some time, I can testify as to its value and efficiency.
Another form of nitric acid plant, which promises to be of considerable service to the manufacturer of nitric acid for the purpose of nitrating, is the invention of the late Mr Manning Prentice, of Stowmarket. Through the kindness
* "The Manufacture of Nitric Acid," Jour. Soc. Chetn. Ind., March 1S93.
46 NITRO-EXPLOSIVES.
of Mr Prentice, I visited his works to see the plant in operation. It consists of a still, divided into compartments or chambers in such a manner that the fluid may pass continuously from one to the other. The nitric acid being continuously separated by distillation, the contents of each division vary — the first containing the full proportion of nitric acid, and each succeeding one less of the nitric acid, until from the overflow of the last one the bisulphate of soda flows away without any nitric acid. The nitrate of soda is placed in weighed quantities in the hopper, whence it passes to the feeder. The feeder is a miniature horizontal pug-mill, which receives the streams of sulphuric acid and of nitrate, and after thoroughly mixing them, delivers them into the still, where, under the influence of heat, they rapidly become a homogeneous liquid, from which nitric acid con- tinuously distils.
Mr Prentice says : " I may point out that while the ordinary process of making nitric acid is one of fractional distillation by time, mine is fractional distillation by space." " Instead of the operation being always at the same point of space, but differing by the successive points of time, I arrange for the differences to take place at different points of space, and these differences exist at one and the same points of time." It is possible with this plant to produce the full product of nitric acid of a gravity of 1.500, or to obtain the acid of varying strengths from the different still- , heads. One of these stills, capable of producing about 4 tons of nitric acid per week, weighs less than 2 tons. It is claimed that there is by their use a saving of more than, two-thirds in fuel, and four-fifths in condensing plant. Further particulars and illustrations will be found in Mr Prentice's paper {Journal of the Society of Chemical Industry, 1894, p. 323).
CHAPTER III. NITRO-CELLULOSE, &c.
Cellulose Properties— Discovery of Gun-Cotton — Properties of Gun-Cotton — Varieties of Soluble and Insoluble Gun-Cottons — Manufacture of Gun- Cotton — Dipping and Steeping —Whirling out the Acid — Washing — Boiling — Pulping — Compressing — The Waltham Abbey Process — Le Bouchet Process — Granulation of Gun-Cotton — Collodion-Cotton — Manu- facture— Acid Mixture used — Cotton used, >S;c. — Nitrated Gun-Cotton — Tonite — Dangers in Manufacture of Gun-Cotton — Trench's Fire-Ex- tinguishing Compound — Uses of Collodion-Cotton — Celluloid — Manu- facture, &.c. — Nitro-Starch, Nitro-Jute, and Nitro-Mannite.
The Nitro-Celluloses. — The substance known as cellu- lose forms the groundwork of vegetable tissues. The cellulose of the woody parts of plants was at one time supposed to be a distinct body, and was called lignine, but they are now regarded as identical. The formula of cellu- lose is (C6H10O:5)x, and it is generally assumed that the molecular formula must be represented by a multiple of the empirical formula, C12H20O10 being often regarded as the minimum. The assumption is based on the existence of a penta-nitrate and the insoluble and colloidal nature of cellulose. Green (Zeit. Farb. Text. Ind., 1904, 3, 97) con- siders these reasons insufficient, and prefers to employ the single formula C0H10O5. Cellulose can be extracted in the pure state, from young and tender portions of plants by first crushing them, to rupture the cells, and then extracting with dilute hydrochloric acid, water, alcohol, and ether in succession, until none of these solvents remove anything more. Fine paper or cotton wool yield very nearly pure cellulose by similar treatment.
|
44-° per cent |
44.2 per cent. |
|
6-3 |
6.4 |
|
497 |
49-4 |
48 NITRO-EXPLOSIVES.
Cellulose is a colourless, transparent mass, absolutely insoluble in water, alcohol, or ether. It is, however, soluble in a solution of cuprammoniac solution, prepared from basic carbonate or hydrate of copper and aqueous ammonia. The specific gravity of cellulose is 1.25 to 1.45. According to Schulze, its elementary composition is expressed by the percentage numbers : —
Carbon Hydrogen Oxygen -
These numbers represent the composition of the ash free cellulose. Nearly all forms of cellulose, however, con- tain a small proportion of mineral matters, and the union of these with the organic portion of the fibre or tissue is of such a nature that the ash left on ignition preserves the form of the original. " It is only in the growing point of certain young shoots that the cellulose tissue is free from mineral constituents" (Hofmeister).
Cellulose is a very inert body. Cold concentrated sulphuric acid causes it to swell up, and finally dissolves it, forming a viscous solution. Hydrochloric acid has little or no action, but nitric acid has, and forms a series of bodies known as nitrates or nitro-celluloses. Cellulose has some of the properties of alcohols, among them the power of forming ethereal salts with acids. When cellulose in any form, such as cotton, is brought into contact with strong nitric acid at a low temperature, a nitrate or nitro product, containing nitryl, or the N02 group, is produced. The more or less complete replacement of the hydroxylic hydrogen by NO., groups depends partly on the concentra- tion of the nitric acid used, partly on the duration of the action. If the most concentrated nitric and sulphuric acids are employed, and the action allowed to proceed for some considerable time, the highest nitrate, known as hexa- nitro-cellulose or gun-cotton, C12H1404(O.N02)6, will be formed ; but with weaker acids, and a shorter exposure to
GUN-COTTON. 49
their action, the tetra and penta and lower nitrates will be formed.*
Besides the nitrate, A. Luck f has proposed to use other esters of cellulose, such as the acetate, benzoate, or butyrate. It is found that cellulose acetate forms with nitro-glycerine a gelatinous body without requiring the addition of a solvent. A sporting powder is proposed composed of 75 parts of cellulose nitrate (13 per cent. N.) mixed with 13 parts of cellulose acetate.
The discovery of gun-cotton is generally attributed to Schonbein (1846), but Braconnot (in 1832) had previously nitrated starch, and six years later Pelouse prepared nitro- cotton and various other nitro bodies, and Dumas nitrated paper, but Schonbein was apparently the first chemist to use a mixture of strong nitric and sulphuric acids. Many chemists, such as Piobert in France, Morin in Russia, and Abel in England, studied the subject ; but it was in Austria, under the auspices of Baron Von Lenk, that the greatest progress was made. Lenk used cotton in the form of yarn, made up into hanks, which he first washed in a solution of potash, and then with water, and after drying dipped them in the acids. The acid mixture used consisted of 3 parts by weight of sulphuric to 1 part of nitric acid, and were prepared some time before use. The cotton was dipped one skein at a time, stirred for a few minutes, pressed out, steeped, and excess of acid removed by wash- ing with water, then with dilute potash, and finally with water. Von Lenk's process was used in England at Faversham (Messrs Hall's Works), but was given up on account of an explosion (1847).
Sir Frederick Abel, working at Stowmarket and Waltham Abbey, introduced several very important improvements into the process, the chief among these being pulping. Having traced the cause of its instability to the presence
* The paper by Prof. Lunge, Jour. Amer. Chan. Soc, 1901, 23 [8], 527-579, contains valuable information on this subject. t Eng. Pat. 24,662, 22nd November 1898.
D
5<D NITRO-EXPLOSIVES.
of substances caused by the action of the nitric acid on the resinous or fatty substances contained in the cotton fibre, he succeeded in eliminating them, by boiling the nitro- cotton in water, and by a thorough washing, after pulping the cotton in poachers.
Although gun-cottons are generally spoken of as nitro- celluloses, they are more correctly described as cellulose nitrates, for unlike nitro bodies of other series, the}7 do not yield, or have not yet done so, amido bodies, on reduction with nascent hydrogen.* The equation of the formation of gun-cotton is as follows : — ■
2(C6H10O5) + 6HNO3 = C12H14O4(NO3)6+6OH2.
Cellulose. Nitric Acid. Gun-Cotton. Water.
The sulphuric acid used does not take part in the reaction, but its presence is absolutely essential to combine with the water set free, and thus to prevent the weakening of the nitric acid. The acid mixture used at Waltham Abbey consists of 3 parts by weight of sulphuric acid of 1.84 specific gravity, and 1 part of nitric acid of 1.52 specific gravity. The same mixture is also used at Stowmarket (the New Explosive Company's Works). The use of weaker acids results in the formation of collodion-cotton and the lower nitrates generally.
The nitrate which goes under the name of gun-cotton is generally supposed to be the hexa-nitrate, and to contain 14.14 per cent, of nitrogen ; but a higher percentage than 13.7 has not been obtained from any sample. It is almost impossible (at any rate upon the manufacturing scale) to make pure hexa-nitro-cellulose or gun-cotton ; it is certain to contain several per cents, of the soluble forms, i.e., lower nitrates. It often contains as much as 15 or 16 per cent., and only from 1 3.07 f to 1 3.6 per cent, of nitrogen.
* " Cellulose," by Cross and Bevan, ed. by W. R. Hodgkinson, p. 9.
t Mr J. J. Sayers, in evidence before the court in the " Cordite Case," says he found 15.2 and 16. 1 per cent, soluble cotton, and 13.07 and 13.08 per cent, nitrogen in two samples of Waltham Abbey gun-cotton.
NITRO-CELLULOSES. 5 1
A whole series of nitrates of cellulose are supposed to exist, the highest member being the hexa-nitrate, and the lowest the mono-nitrate. Gun-cotton was at one time regarded as the tri-nitrate, and collodion-cotton as the di-nitrate and mono-nitrate, their respective formula being given as follows : —
Mono-nitrocellulose - - CfiH9(NO.,)03 = 6.763 per cent, nitrogen.
Di-nitro-cellulose - - - C6H8(N02)203 = 11. 11 Tri-nitro-cellulose - - - C6H7(N02)305 = 14.14 ,, ,,
But gun-cotton is now regarded as the hexa-nitrate, and collodion-cotton as a mixture of all the other nitrates. In fact, chemists are now more inclined to divide nitro- cellulose into the soluble and insoluble forms, the reason being that it is quite easy to make a nitro-cellulose entirely soluble in a mixture of ether-alcohol, and yet containing as high a percentage of nitrogen as 12.6 ; whereas the di- nitrate* should theoretically only contain n.ii per cent. On the other hand, it is not possible to make gun-cotton with a higher percentage of nitrogen than about 13.7, even when it does not contain any nitro-cotton that is soluble in ether-alcohol. j" The fact is that it is not at present possible to make a nitro-cellulose which shall be either entirely soluble or entirely insoluble, or which will contain the theoretical content of nitrogen to suit any of the above formulae for the cellulose nitrates. Prof. G. Lunge gives the following list of nitration products of cellulose : —
* The penta-nitrate C12H1505(N03)3 = 12.75 Per cent, nitrogen.
t In the Cordite Trial (1894) Sir F. A.Abel said, " Before 188S there was a broad distinction between soluble and insoluble nitro- cellulose, collodion-cotton being soluble (in ether-alcohol) and gun- cotton insoluble." Sir H. E. Roscoe, " That he had been unable to make a nitro-cotton with a higher nitrogen content than 13.7.'"' And Professor G. Lunge said, " Gun-cotton always contained soluble cotton, and vice versa." These opinions were also generally con- firmed by Sir E. Frankland, Sir W. Crookes, Dr Armstrong, and others.
|
C,4Ho902,,(N02)n - |
i3-5o ,, |
|
C24H30O20(NO2)10 = |
12.78 ,, |
|
C.,4H31O,0(NCX,)9 = |
11.98 ,, |
|
C24H32O20(NO2)8 = |
11-13 ,, |
|
C24H33O,0(NO2)* = |
10.19 ., |
|
C24H34O20(NO2)6 - |
9.17 ,. |
|
C24H85O20(NO2)5 = |
S.04 ,, |
|
C24H36O20(NO2)4 = |
6-77 „ |
52 NITRO-EXPLOSIVES.
Dodeca-nitro-cellulose - - G24H28O20(NO2)12 = 14. 16 per cent, nitrogen.
( = old tri-nitro-cellulose) Endeca-nitro-cellulose - Deca-nitro-cellulose Ennea-nitro-cellulose Octo-nitro-cellulose
( = old di-nitro-cellulose) Hepta-nitro-cellulose Hexa-nitro-cellulose Penta-nitro-cellulose Tetra-nitro-cellulose
( = old mono-nitro-cellulose)
It is not unlikely that a long series of nitrates exists. It is at any rate certain that whatever strength of acids may be used, and whatever temperature or other conditions may be present during the nitration, that the product formed always consists of a mixture of the soluble and insoluble nitro-cellulose.
Theoretically 100 parts of cotton by weight should produce 2 1 8.4 parts of gun - cotton, but in practice the yield is a good deal less, both in the case of gun-cotton or collodion-cotton. In speaking of soluble and insoluble nitro-cellulose, it is their behaviour, when treated with a solution consisting of 2 parts ether and 1 of alcohol, that is referred to. There is, however, another very important difference, and that is their different solubility in nitro- glycerine. The lower nitrates or soluble form is soluble in nitro-glycerine under the' influence of heat, a temperature of about 50° C. being required. At lower temperatures the dissolution is very imperfect indeed ; and after the materials have been left in contact for days, the threads of the cotton can still be distinguished. The insoluble form or gun-cotton is entirely insoluble in nitro-glycerine. It can, however, be made to dissolve* by the aid of acetone or acetic ether. Both or rather all the forms of nitro-cellulose can be dissolved in acetone or acetic ether. They also
* Or rather to form a transparent jelly,
NITRO-CELLULOSES. 53
dissolve in concentrated sulphuric acid, and the penta-nitrate in nitric acid at about 80° or 90° C.
The penta-nitrate may be obtained in a pure state by the following process, devised by Eder : — The gun-cotton is dissolved in concentrated nitric acid at 90" C, and re- precipitated by the addition of concentrated sulphuric acid. After cooling to 0° C, and mixing with a larger volume of water, the precipitated nitrate is washed with water, then with alcohol, dissolved in ether-alcohol, and again precipitated with water, when it is obtained pure. This nitrate is soluble in ether-alcohol, and slightly in acetic acid, easily in acetone, acetic ether, and methyl- alcohol, insoluble in alcohol. Strong potash (KOH) solution converts into the di-nitrate C12H1S0S(N03)2. The hexa-nitrate is not soluble in acetic acid or methyl-alcohol.
The lower nitrates known as the tetra- and tri-nitrates are formed together when cellulose is treated with a mixture of weak acids, and allowed to remain in contact with them for a very short time (twenty minutes). They cannot be separated from one another, as they all dissolve equally in ether-alcohol, acetic ether, acetic acid, methyl- alcohol, acetone, amyl acetate, &c.
As far as the manufacture of explosive bodies is con- cerned, the two forms of nitro-cellulose used and manu- factured are gun-cotton or the hexa-nitrate (once regarded as tri-nitro-cellulose), which is also known as insoluble gun- cotton, and the soluble form of gun-cotton, which is also known as collodion, and consists of a mixture of several of the lower nitrates. It is probable that it chiefly consists, however, of the next highest nitrate to gun-cotton, as the theoretical percentage of nitrogen for this body, the penta-nitrate, is 12.75 per cent., and analyses of com- mercial collodion-cotton, entirely soluble in ether-alcohol, often give as high a percentage as 12.6.
We shall only describe the manufacture of the two forms known as soluble and insoluble, and shall refer to them under their better known names of cun-cotton and
54 NITRO-EXPLOSIVES.
collodion-cotton. The following would, however, be the formulae* and percentage of nitrogen of the complete series : —
|
Hexa-nitro- cellulose |
C12H1404(N03)fi |
14. 14 per |
cent, nitrogen |
|
Penta-nitro-cellulose |
- C12H1505(N03)5 |
12-75 |
> j? |
|
Tetra-nitro-cellulose |
C12H1606(NOs)4 |
11. 11 |
, ,, |
|
Tri-nitro -cellulose |
- C^HtfCtyNO,), |
9- '3 |
> » > |
|
Di-nitro-cellulose |
C12Hls08(NO3)2 |
7-65 |
, ,, |
|
Mono-nitro-cellulose |
C12H1909(N03) |
3.S0 |
>> >> |
Properties of Gun-Cotton. — The absolute density of gun-cotton is 1.5. When in lumps its apparent density is 0.1 ; if twisted into thread, 0.25 ; when subjected, in the form of pulp, to hydraulic pressure, 1.0 to 1.4. Gun-cotton preserves the appearance of the cotton from which it is made. It is, however, harsher to the touch ; it is only slightly hygroscopic (dry gun-cotton absorbs 2 per cent, of moisture from the air). It possesses the property of becoming electrified by friction. It is soluble in acetic ether, amyl acetate, and acetone, insoluble in water, alcohol, ether, ether-alcohol, methyl-alcohol, &c. It is very explo- sive, and is ignited by contact with an ignited body, or by shock, or when it is raised to a temperature of 1720 C. It burns with a yellowish flame, almost without smoke, and leaves little or no residue. The volume of the gases formed is large, and consists of carbonic acid, carbonic oxide, nitrogen, and water gas. Compressed gun-cotton when ignited often explodes when previously heated to 100" C.
Gun-cotton kept at 8o° to ioo° C. decomposes slowly, and sunlight causes it to undergo a slow decomposition. It can, however, be preserved for years without under- going any alteration. It is very susceptible to explosions by influence. For instance, a torpedo, even placed at a
* Berthelot takes C24H40Oo0 as the formula of cellulose ; and M. Vieille regards the highest nitrate as (Cn4H18(N03H)1i09). Compt. Rend., 1882, p. 132.
PROPERTIES OF GUN-COTTON. 55
long distance, may explode a line of torpedoes charged with gun-cotton. The velocity of the propagation of the explosion in metallic tubes filled with pulverised gun- cotton has been found to be from 5,000 to 6,000 mms. per second in tin tubes, and 4,000 in leaden tubes (Sebert).
Gun-cotton loosely exposed in the open air burns eight times as quickly as powder (Piobert). A thin disc of gun-cotton may be fired into from a rifle without explosion ; but if the thickness of the disc be increased, an explosion may occur. The effect of gun-cotton in mines is very nearly the same as that of dynamite for equal weights. It requires, however, a stronger detonator, and it gives rise to a larger quantity of carbonic oxide gas. Gun-cotton should be neutral to litmus, and should stand the Government heat test — temperature of 150' F. for fifteen minutes (see page 249^. In the French Navy gun-cotton is submitted to a heat test of 65" C. ( = 149° F.) for eleven minutes. It should contain as small a per- centage of soluble nitro-cotton and of non-nitrated cotton as possible.
The products of perfectly detonated gun-cotton may be expressed by the following equation : —
2C1.2HuO/X03)6= iSCO + 6C02+ I4H.O+ 12X.
It does not therefore contain sufficient oxvgen for the complete combustion of its carbon. It is for this reason that when used for mining purposes a nitrate is gene- rally added to supply this defect (as, for instance, in tonite). It tends also to prevent the evolution of the poisonous gas, carbonic oxide. The success of the various gelatine explosives is due to this fact, viz., that the nitro- glycerine has an excess of oxygen, and the nitro-cotton too little, and thus the two explosives help one another.
In practice the gases resulting from the explosion of gun-cotton are — Carbonic oxide, 28.55 '■> carbonic acid, 19.11 ; marsh gas (CHj, 11. 17; nitric oxide, 8.83 ; nitro- gen, 8.56; water vapour, 21.93 per cent. The late Mr
56 NITRO-EXPLOSIVES.
E. O. Brown, of Woolwich Arsenal, discovered that per- fectly wet and uninflammable compressed gun-cotton could be easily detonated by the detonation of a priming charge of the dry material in contact with it. This ren- dered the use of gun-cotton very much safer for use as a military or mining explosive.
As a mining explosive, however, gun-cotton is now chiefly used under the form of tonite, which is a mixture of half gun-cotton and half barium nitrate. This material is sometimes spoken of as " nitrated gun-cotton." The weight of gun-cotton required to produce an equal effect either in heavy ordnance or in small arms is to the weight of gunpowder in the proportion of I to 3, i.e., an equal weight of gun-cotton would produce three times the effect of gunpowder. Its rapidity of combustion, however, requires to be modified for use in firearms. Hence the lower nitrates are generally used, or such compounds as nitro-lignose, nitrated wood, &c, are used.
The initial pressure produced by the explosion of gun- cotton is very large, equal to 18,135 atmospheres, and 8,740 kilogrammes per square centimetre for 1 kilo., the heat liberated being 1,075 calories (water liquid), or 997.7 cals. (water gaseous), but the quantity of heat liberated changes with the equation of decomposition. According to Berthe- lot,* the heat of formation of collodion-cotton is 696 cals. for 1,053 grins. , or 661 cals. for 1 kilo. The heat liberated in the total combustion of gun-cotton by free oxygen at constant pressure is 2,633 cals. for 1,143 grms., or for I kilo, gun-cotton 2,302 cals. (water liquid), or 2,177 cals- (water gaseous). The heat of decomposition of gun-cotton in a closed vessel, found by experiment at a low density of charge (0.023), amounts to 1,071 cals. for 1 kilo, of the substance, dry and free from ash. To obtain the maximum effect of gun-cotton it must be used in a compressed state, for the initial pressures are thereby increased. Wet gun-
* "Explosives and their Power," trans, by Hake and M'Nab.
MANUFACTURE OF GUN-COTTON. 57
cotton is much less sensitive to shock than dry. Paraffin also reduces its liability to explode, so also does camphor. The substance known as celluloid, a variety of nitro- cellulose nearly corresponding to the formula C24H24 (N03H)8012, to which camphor and various inert sub- stances are added, so as to render it non-sensitive to shock, may be worked with tools, and turned in the lathe in the same manner as ivory, instead of which material celluloid is now largely used for such articles as knife handles, combs, &c. Celluloid is very plastic when heated towards 150° C, and tends to become very sensitive to shock, and in large quantities might become explosive during a fire, owing to the general heating of the mass, and the con- sequent evaporation of the camphor. When kept in the air bath at 135° C, celluloid decomposes quickly. In an experiment (made by M. Berthelot) in a closed vessel at 135° C.j and the density of the charge being 0.4, it ended in exploding, developing a pressure of 3,000 kilos. A large package of celluloid combs also exploded in the guard's van on one of the German railways a few years ago. Although it is not an explosive under ordinary circum- stances, or even with a powerful detonator, considerable care should be exercised in its manufacture.
The Manufacture of Gun-Cotton. — The method used for the manufacture of gun-cotton is that of Abel (Spec. No. 1 102, 20. 4. 65). It was worked out chiefly at Stow- market* and Waltham Abbey,f but has in the course of time undergone several alterations. These modifications have taken place, however, chiefly upon the Continent, and relate more to the apparatus and machinery used than to any alteration in the process itself. The form of cellulose used is cotton-waste,^ which consists of the clippings and
* The New Explosive Co. Works, t Royal Gunpowder Factory.
t Costs from ^10 to ,£25 a ton. In his description of the "Pre- paration of Cotton-waste for the Manufacture of Smokeless Powder,'
58 NITRO-EXPLOSIVES.
waste material from cotton mills. After it has been cleaned and purified from grease, oil, and other fatty substances by treatment with alkaline solutions, it is carefully picked over, and every piece of coloured cotton fag or string carefully removed. The next operation to which it is submitted has for its object the opening up of the material. For this purpose it is put through a carding machine, and afterwards through a cutting machine, whereby it is reduced to a state suitable for its subsequent treatment with acids, that is, it has been cut into short lengths, and the fibres opened up and separated from one another.
Drying the Cotton. — This operation is performed in either of two ways. The cotton may either be placed upon shelves in a drying house, through which a current of hot air circulates, or dried in steam-jacketed cylinders. It is very essential that the cotton should be as dry as possible before dipping in the acids, especially if a wholly "insoluble" nitro-cellulose is to be obtained. After drying it should not contain more than 0.5 per cent, of moisture, and less than this if possible. The more general method of drying the cotton is in steam-jacketed tubes, i.e., double cylinders of iron, some .5 feet long and il foot wide. The cotton is placed in the central chamber (Fig. 10), while steam is made to circulate in the surrounding jacket, and keeps the whole cylinder at a high temperature (steam pipes may be
A. Hertzog states that the German military authorities require a cotton which when thrown into water sinks in two minutes ; when nitrated, does not disintegrate ; when treated with ether, yields only 0.9 per cent, of fat ; and containing only traces of chlorine, lime, magnesia, iron, sulphuric acid, and phosphoric acid. If the cotton is very greasy, it must be first boiled with soda-lye under pressure, washed, bleached with chlorine, washed, treated with sulphuric acid or HC1, again washed, centrifugaled, and dried ; if very greasy indeed a preliminary treatment with lime-water is desirable. See also " Inspec- tion of Cotton- Waste for Use in the Manufacture of Gun-cotton," by C. E. Munro, Jour. Am. Chem. Sol., 1895, 17, 783.
DRYING THE COTTON.
59
coiled round the outside of an iron tube, and will answer equally well). By means of a pipe which communicates with a compressed air reservoir, a current of air enters at the bottom, and finds its way up through the cotton, and helps to remove the moisture that it contains. The raw cotton generally contains about 10 per cent, of moisture and should be dried until it contains only <\ 11 /?
\ per cent, or less. For this it will generally have to remain in the dry- ing cylinder for about five hours. At the end of that time a sample should be taken from the top of the cylinder, and dried in the water oven(lOO° C.*) for an hour to an hour and a half, and re-weighed, and the moisture then re- maining in it calculated.
It is very convenient to have a large copper water oven, containing a lot of small separate compartments,' large enough to hold about a handful of the cotton, and each compartment numbered, and corresponding to one of the drying cylinders. The whole apparatus should be fixed against the wall of the laboratory, and may be heated by bringing a small steam pipe from the boiler-house. It is useful to have a series of copper trays, about 3 inches by 6 inches, numbered to correspond to the divisions in the steam oven, and exactly fitting them. These trays can then be taken by a boy to the drying cylinders, and a handful of the cotton from each placed in them, and afterwards brought to the laboratory and weighed (a boy can do this very well), placed in their respective divisions of the oven, and left for one to one and a half hours, and re-weighed.
When the cotton is found to be dry the bottom of the
Fig. 10. — Cottox Drier.
* It is dried at i8o'J C. at Waltham Abbey, in a specially con- structed drying chamber.
60 NITRO-EXPLOSIVES.
drying cylinder is removed, and the cotton pushed out from the top by means of a piece of flat wood fixed on a broom-handle. It is then packed away in galvanised-iron air-tight cases, and is ready for the next operation. At some works the cotton is dried upon shelves in a drying house through which hot air circulates, the shelves being of canvas or of brass wire netting. The hot air must pass under the shelves and through the cotton, or the process will be a very slow one.
Dipping and Steeping. — The dry cotton has now to be nitrated. This is done by dipping it into a mixture of nitric and sulphuric acids. The acids used must be strong, that is, the nitric acid must be at least of a gravity of 1.53 to 1.52, and should contain as little nitric oxide as possible. The sulphuric acid must have a specific gravity of 1.84 at 1 5° C, and contain about 97 per cent, of the mono-hydrate (H2S04). In fact, the strongest acids obtainable should be used when the product required is gun-cotton, i.e., the highest nitrate.
The sulphuric acid takes no part in the chemical re- action involved, but is necessary in order to combine with the water that is liberated in the reaction, and thus to main- tain the strength of the nitric acid. The reaction which takes place is the following : —
2(C6H10O5) + 6HNO3 = C12H1A(NO3)6+6H2O.
324 378 = 594 108.
Cellulose. Gun-Cotton.
Theoretically,* therefore, 1 part of cellulose should form 1.8 part of gun-cotton. Practically, however, this is never obtained, and 1.6 lb. from 1 lb. of cellulose is very good working. The mixture of acids used is generally 1 to 3, or 25 per cent, nitric acid to 75 per cent, sulphuric acid.
* 594Xi = l8
324
STEEPING THE COTTON.
6l
The dipping is done in cast-iron tanks (Fig. Il), a series of which is arranged in a row, and cooled bv a stream of
Fig. ii.— Tank for Dipping Cotton.
cold water flowing round them. The tanks hold about 12 gallons, and the cotton is dipped in portions of I lb. at a time. It is thrown into the acids, and the workman
Fig. 12. — The Cooling Pit;
moves it about for about three minutes with an iron rabble. At the end of that time he lifts it up on to an iron grating,
62
NITRO-EXPLOSIVES.
just above the acids, fixed at the back of the tank, where by means of a movable lever he gently squeezes it, until it contains about ten times its weight of acids (the I lb. weighs 10 lbs.). It is then transferred to earthenware pots to steep.
Steeping'. — The nitrated cotton, when withdrawn from the dipping tanks, and still containing an excess of acids, is put into earthenware pots of the shape shown in Figs. 12 and 13. The lid is put on, and the pots placed in rows in large cooling pits, about a foot deep, through which a stream of water is con- stantly flowing. These pits form the floor of the steeping house. The cotton remains in these pots for a period of forty-eight hours, and must be kept cool. Between 1 8° and 19° C. is the highest temperature desirable, but the cooler the pots are kept the better. At the end of forty-eight hours the chemical reaction is com-
Fig. 13. — Cotton Steeping Pot.
MANLOVEALLIOTTSkCSL',
plete, and the cotton is or should be wholly converted into nitro-cellulose ; that is, there should be no unnitrated cotton.
Whirling Out the Acid. — The next operation is to remove the excess of acid. This is done by placing the
WASHING GUN-COTTON. 63
contents of two or three or more pots into a centrifugal hydro-extractor (Fig. 14), making 1,000 to 1,500 revolutions per minute. The hydro-extractor consists of a machine with both an inner cylinder and an outer one, both revolv- ing in concert and driving outwardly the liquid to the chamber, from which it runs away by a discharge pipe. The wet cotton is placed around the inner cone. The cotton, when dry, is removed, and at once thrown into a large tank of water, and the waste acids are collected in a tank.*
Washing". — The cotton has now to be carefully washed. This is done in a large wooden tank filled with water. If, however, a river or canal runs through the works, a series of wooden tanks, the sides and bottoms of which are pierced with holes, so as to allow of the free circulation of water, should be sunk into a wooden platform that overhangs the surface of the river in such a way that the tanks are immersed in the water, and of course always full. During the time that the cotton is in the water a workman turns it over constantly with a wooden paddle. A stream of water, in the form of a cascade, should be allowed to fall into these tanks. The cotton may then be thrown on to this stream of water, which, falling some height, at once carries the cotton beneath the surface of the water. This pro- ceeding is necessary because the cotton still retains a large excess of strong acids, and when mixed with water gives rise to considerable heat, especially if mixed slowly with water. After the cotton has been well washed, it is a^ain
* Care must be taken in hot weather that the gun-cotton does not fire, as it does sometimes, directly the workman goes to remove it after the machine is stopped. It occurs more often in damp weather. Dr Schiipphaus, of Brooklyn, U.S.A., proposes to treat the waste acids from the nitration of cellulose by adding to them sulphuric anhydride and nitric acid. The sulphuric anhydride added converts the water liberated from the cellulose into sulphuric acid.
64
NITRO-EXPLOSIVES.
wrung out in a centrifugal machine, and afterwards allowed to steep in water for some time.
Boiling". — The washed cotton is put into large iron boilers with plenty of water, and boiled for some time at ioo° C. In some works lead-lined tanks are used, into which a steam pipe is led. The soluble impurities of un-
Fig. i5«. — The Beater for Gun-Cotton.
stable character, to which Sir F. A. Abel traced the liability of gun-cotton to instability, are thereby removed. These impurities consist of the products formed by the action of nitric acid on the fatty and resinous substances contained in the cotton fibres. The water in the tanks should be every now and again renewed, and after the first few boilings the water should be tested with litmus paper until they are no longer found to be acid.
TULPING GUN-COTTON.
65
Pulping. — The idea of pulping is also due to Abel. By its means a very much more uniform material is obtained. The process is carried out in an apparatus known as a "Beater" or " Hollander" (Fig. 15, a, b). It consists of a kind of wooden tank some 2 or 3 feet deep of an oblong shape, in which a wheel carrying a series of knives is made to revolve, the floor of the tank being sloped up so as to almost touch the revolving wheels. This part of the floor, known as the " craw," is a solid piece of oak, and a box of knives is fixed into it, against which the knives in the revolving wheel are pressed. The beater is divided into two parts — the working side, in which the cotton is cut and torn between the knife edges in the revolving cylinder and those in the box ; and the running side, into which the cotton passes after passing under the cylinder. The wheel is generally boxed in to prevent the cotton from being thrown out during its revolution. The cotton is thus in constant motion, continually travelling round, and passing between the knives in the revolving cylinder and those in
Fig. 15^. — Wheel of Beater.
Fig. 16a. — Poacher for Washing Gun-Cotton.
the box fixed in the wooden block beneath it. The beater is kept full of water, and the cotton is gradually reduced to a condition of pulp. The wheel revolves at the rate of 100 to 150 times a minute.
When the gun-cotton is judged to be sufficiently fine, the contents of the beater are run into another very similar piece of machinery, known as the " poacher " (Fig. 16, a, b, c),
E
66
NITRO-EXPLOSIVES.
in which the gun-cotton is continuously agitated together with a large quantity of water, which can be easily run off and replaced as often as required. When the material is first run into the poacher from the beater, the water with
Fig. i63. — Plan of the Poacher.
which it is then mixed is first run away and clean water added. The paddle wheel is then set in motion, and at intervals fresh water is added. There is a strainer at the bottom of the poacher which enables the water to be drawn off without disturbing the cotton pulp. After the gun-
Fig. 16c. — Another Form of Poacher.
cotton has been in the poacher for some time, a sample should be taken by holding a rather large mesh sieve in the current for a minute or so. The pulp will thus partly pass through and partly be caught upon the sieve, and an average sample will be thus obtained. The sample is
COMPRESSING GUN-COTTON. 6j
squeezed out by hand, bottled, and taken to the laboratory to be tested by the heat test for purity. It first, however, requires to be dried. This is best done by placing the sample between coarse filter paper, and then putting it under a hand-screw press, where it can be subjected to a tolerably severe pressure for about three minutes. It is then rubbed up very finely with the hands, and placed upon •a paper tray, about 6 inches by 4 -J- inches, which is then placed inside a water oven upon a shelf of coarse wire gauze, the temperature of the oven being kept as near as possible to 120° F. (49° C), the gauze shelves in the oven being kept about 3 inches apart. The sample is allowed to remain at rest for fifteen minutes in the oven, the door of which is left wide open. After the lapse of fifteen minutes the tray is removed and exposed to the air of the laboratory (away from acid fumes) for two hours, the sample being at some point within that time rubbed upon the tray with the hand, in order to reduce it to a fine and uniform state of division. Twenty grains (1.296 grm.) are used for the test. (See Heat Test, page 249.)
If the gun-cotton sample removed from the poacher stands the heat test satisfactorily, the machine is stopped, and the water drained off. The cotton is allowed some little time to drain, and is then dug out by means of wooden spades, and is then ready for pressing. The poachers hold about 2,000 lbs. of material, and as this represents the products of many hundred distinct nitrating operations, a very uniform mixture is obtained. Two per cent, of carbonate of soda is sometimes added, but it is not really necessary if the cotton has been properly washed.
Compressing Gun-Cotton. — The gun-cotton, in the state in which it is removed from the poacher, contains from 28 to 30 per cent, of water. In order to remove this, the cotton has to be compressed by hydraulic power. The dry compressed gun-cotton is packed in boxes containing
68
NITROEXPLOSIVES.
2,500 lbs. of dry material. In order to ascertain how much of the wet cotton must be put into the press, it is necessary to determine the percentage of water. This may be done by drying 2,000 grains upon a paper tray (previously dried at ioo° C.) in the water oven at 100° C. for three hours, and re-weighing and calculating the percentage of water. It is then easy to calculate how, much of the wet gun-cotton must be placed in the hopper of the press in order to obtain a block of compressed cotton of the required weight.
Fig. 17. — Old Method, ioo Pieces.
Fig. 18. — New Method. One Solid Block.
Various forms of presses are used, and gun-cotton is sent out either as solid blocks, compressed discs, or in the form of an almost dry powder, in zinc-lined, air-tight cases. The discs are often soaked in water after compression until they have absorbed 25 per cent, of moisture.
At the New Explosives Company's Stowmarket Works large solid blocks of gun-cotton are pressed up under a new process, whereby blocks of gun-cotton, for use in submarine mines or in torpedo warheads, are produced. Large charges
COMPRESSING GUN-COTTON. 69
of compressed gun-cotton have hitherto been built up from a number of suitably shaped charges of small dimensions (Fig. 17), as it has been impossible to compress large charges in a proper manner. The formation of large-sized blocks of gun-cotton was the invention of Mr A. Hollings. Prior to the introduction of this method, 8 or 9 lbs. had been the limit of weight for a block. This process has been perfected at the Stowmarket factory, where blocks varying from the armour-piercing shell charge of a few ounces up to blocks of compressed gun-cotton mechanically true, weighing 4 to 5 cwts. for torpedoes or submarine mines, are now produced. At the same time the new process ensures a uniform density throughout the block, and per- mits of any required density, from 1.4 downwards, being attained ; it is also possible exactly to regulate the per- centage of moisture, and to ensure its uniform distribution. The maximum percentage of moisture depends, of course, upon the density. By the methods of compression gun- cotton blocks hitherto employed, blocks of a greater thick- ness than 2 inches, or of a greater weight than 9 lbs., could not be made, but with the new process blocks of any shape, size, thickness, or weight that is likely to be required can be made readily and safely. The advantages which are claimed for the process may be enumerated as follows : — (1.) There is no space wasted, as in the case with built-up charges, through slightly imperfect contact between the individual blocks, and thus either a heavier charge — i.e., about 1 5 per cent, more gun-cotton — can be got into the same space, or less space will be occupied by a charge of a given weight. (2.) The metallic cases for solid charges may be much lighter than for those built-up, since with the former their function is merely to prevent the loss of moisture from wet gun-cotton, or to prevent the absorption of moisture by dry gun-cotton. They can thus be made lighter, as the solid charge inside will prevent deformation during transport. With built-up charges the case must be strong enough to prevent damage, either to itself or to the
70
NITRO-EXPLOSIVES.
charge it contains. For many uses a metal case, however light, may be discarded, and one of a thin waterproof material substituted. (3.) The uniform density of charges made by this process is very favourable to the complete and effective detonation of the entire mass, and to the presence of the uniform amount of moisture in every part of the charge. (4.) Any required density, from the maximum
Fig. 19. — A 4-CwT. Block of Gun-Cotton being taken from Hydraulic Press.
downwards, may be obtained with ease, and any required amount of moisture left in the charge. These points are of great importance in cases where, like torpedo charges, it is essential to have the centre of gravity of the charge in a predetermined position both vertically and longitudinally, and the charge so fixed in its containing case that the centre of gravity cannot shift. The difficulty of ensuring this with a large torpedo charge built up from a number
WALTHAM ABBEY PROCESS. 7 1
of discs and segments is well known. Even with plain cylindrical or prismatic charges a marked saving in the process of production is effected by this new system. The charges being in one block they are more easily handled for the usual periodical examination, and they do not break or chafe at the edges, as in the case of discs and cubes in built-up charges. A general view of the press is given in Fig. 19. The gun-cotton in a container is placed on a cradle fixed at an angle to the press. The mould is swivelled round, and the charge pushed into it with a rammer, and it is then swivelled back into position. The mould is made up of a number of wedge pieces which close circumferentially on the enclosed mass, which is also sub- jected to end pressure. Holes are provided for the escape of water.
The Waltham Abbey Process. — At the Royal Gun- powder Factory, Waltham Abbey, the manufacture of gun- cotton has been carried out for many years. The process used differs but little from that used at Stowmarket. The cotton used is of a good quality, it is sorted and picked over to remove foreign matters, &c, and is then cut up by a kind of guillotine into 2-inch lengths. It is then dried in the following manner. The cotton is placed upon an end- less band, which conducts it to the stove, or drying closet, a chamber heated by means of hot air and steam traps to about 1800 F. ; it falls upon a second endless band, placed below the first ; it travels back again the whole length of the stove, and so on until delivered into a receptacle at the bottom of the farther end, where it is kept dry until required for use. The speed at which the cotton travels is 6 feet per minute, and as the length of the band travelled amounts to 126 feet, the operation of drying takes twenty- one minutes. One and a quarter lb. are weighed out and placed in a tin box ; a truck, fitted to receive a number of these boxes, carries it along a tramway to a cool room, where it is allowed to cool.
72 NITRO-EXPLOSIVES.
Dipping. — Mixed acids are used in the proportion of i to 3, specific gravity nitric acid 1.52, and sulphuric acid 1.84. The dipping tank is made of cast iron, and holds 220 lbs. of mixed acids, and is surrounded on three sides by a water space in order to keep it cool. The mixed acids are stored in iron tanks behind the dipping tanks, and are allowed to cool before use. During the nitration, the temperature of the mixed acids is kept at 70° F., and the cotton is dipped in quantities of i| lb. at a time. It is put into a tin shoot at the back of the dipping tank, and raked into the acids by means of a rabble. It remains in the acids for five or six minutes, and is then removed to a grating at the back, pressed and removed. After each charge of cotton is removed from the tank, about 14 lbs. of fresh mixed acids are added, to replace amount removed by charge. The charge now weighs, with the acids retained by it, 1 5 lbs. ; it is now placed in the pots, and left to steep for at least twenty-four hours, the temperature being kept as low as possible, to prevent the formation of soluble cotton, and also prevent firing. The proportion of soluble formed is likely to be higher in hot weather than cold. The pots must be covered to prevent the absorption of moisture from the air, or the accidental entrance of water, which would cause decomposition, and consequent fuming off, through the heat generated by the action of the water upon the strong acids.
The excess of acids is now extracted by means of hydro-extractors, as at Stowmarket. They are worked at 1,200 revolutions per minute, and whirled for five minutes (iOo lbs. of waste acids are removed from each charge dipped). The charge is then washed in a very similar manner to that previously described, and again wrung out in a centrifugal extractor (1,200 revolutions per minute). The gun-cotton is now boiled by means of steam in wooden tanks for eight hours ; it is then again wrung out in the extractors for three minutes, boiled for eight hours more, and again wrung out ; it is then sent to the beater and
Thomson's gun-cotton process. 73
afterwards to the poacher. The poachers hold 1,500 gals. each, or 18 cwt. of cotton. The cotton remains six hours in the poachers. Before moulding, 500 gals, of water are run into the poacher, and 500 gals, of lime water containing 9 lbs. of whiting and 9 gals, of a caustic soda solution. This mixture is of such a strength that it is calculated to leave in the finished gun-cotton from 1 to 2 per cent, of alkaline matter.
By means of vacuum pressure, the pulp is now drawn off and up into the stuff chest — a large cylindrical iron tank, sufficiently elevated on iron standards to allow room for the small gauge tanks and moulding apparatus below. It holds the contents of one poacher (18 cwt.), and is provided with revolving arms to keep the pulp stirred up, so that it may be uniformly suspended in water.
Recently a new process, invented by J. M. and W. T. Thomson (Eng. Pat. No. 8,278, 1903), has been introduced at the Waltham x*\bbey Factory. The object of this inven- tion is the removal of the acids of nitration from the nitrated material after the action has been completed, and without the aid of moving machinery, such as presses, rollers, centrifugals, and the like. The invention consists in the manufacture of nitrated celluloses by removing the acids from the nitrated cellulose directly by displacement without the employment of either pressure or vacuum or mechanical appliances of any kind, and at the same time securing the minimum dilution of the acids. It was found that if water was care- fully run on to the surface of the acids in which the nitro- cellulose is immersed, and the acids be slowly drawn off at the bottom of the vessel, the water displaces the acid from the interstices of the nitro-cellulose without any undesirable rise in temperature, and with very little dilution of the acids. By this process almost the whole of the acid is recovered in a condition suitable for concentration, and the amount of water required for preliminary washing is very greatly reduced. The apparatus which is used for the purpose consists of a cylindrical or rectangular vessel constructed
74
NITRO-EXPLOSIVES.
with a perforated false bottom and a cock at its lowest point for running off the liquid. Means are also provided to enable the displacing water to be run quietly on to the surface of the nitrating acids.*
The apparatus is shown in Fig. 20, side elevation, and in Fig. 21 a plan of the nitrating vessel and its accessories
Fig. 20. — Sectional Elevation of Thomson's Apparatus, a, Tank ; 6, False Bottom; c, Bottom; c', Ribs; d, Draining Outlet; c, Grid; f. Troughs, with Aprons £-; /;, Pipe, with Branches h\ leading to Troughsy; k\ Outlet Pipe of the Sulphuric Acid Tank k\ I, Water Supply Pipe; ;;/, Pipe to supply of Nitrating Acids ; o, Perforations of Troughy" ; /, Cock to remove Acid.
is given. In Fig. 20 is shown in sectional elevation one of the trough devices for enabling liquids to be added to those in the nitrating vessel without substantial disturbance. In carrying out this invention a rectangular lead-lined or earthenware tank a is employed, having a false bottom &, supported by ribs c, over the real bottom c, which slopes down to a draining outlet pipe d, provided with a perforated
* In a further patent (Eng. Pat. 7,269, 1903, F. L. Natham), J. M. Thomson and W. T. Thomson propose by use of alcohol to replace the water, used in washing nitro-cellulose, and afterward to remove the alcohol by pressing and centrifuging.
THOMSON'S APPARATUS.
75
grid or plate e, adapted to prevent choking of the outlet. Suitably supported near the top of the vessel a are pro- vided two troughs/^ having depending aprons g, a pipe h has two branches k ', leading to the troughs/! This pipe h is adapted to be connected by a rubber pipe either to the outlet pipe k' of the sulphuric acid tank k or the water supply pipe /. The nitrating acids are supplied through the pipe m. A charge of mixed nitrating acids is introduced into the vessel a say up to the level n, and the dry cellulose
Fig. 21. — Plan of Thomson's Apparatus, a, Tank; b, False Bottom; c' , Ribs ; c, Grid;/", Troughs; g-, Aprons; h and h' , Pipes to Troughs f\ k, Sulphuric Acid Tank ; m, Pipe to Nitrating Acids Tank ; o, Perforations of Troughs ; p, Cock to remove Acid.
thrown into the acids in small quantities at a time, being pushed under the surface in the usual way.
A thin layer, say half an inch, of a suitable liquid, preferably sulphuric acid, of a gravity not exceeding that of the waste acid to be produced, is run carefully on the top of the acids by means of the troughs f, which are perforated as shown at o, so that the sulphuric acid runs down the aprons g, and floats on the nitrating acids. The
y6 NITRO-EXPLOSIVES.
whole is then allowed to stand till nitration has been com- pleted. Water is then supplied to the troughs by way of the pipes /, h, and //, and is allowed to float very gently over the surface of the sulphuric acid, and when a sufficient layer has been formed, the cock p at the bottom of the apparatus is opened, and the acid slowly drawn off, water being supplied to maintain the level constant. It is found that the rate of displacement of the acids is a factor which exerts a considerable influence on the properties of the resulting nitro-cellulose, and affords a means of regulating the temperature of displacement. A rate of displacement which has been found suitable is about two inches in depth of the vessel per hour when treating highly nitrated cellu- loses, but this rate may, in some cases, be considerably increased. The flow of water at the top of the apparatus is regulated so that a constant level is maintained. By this means the water gradually and entirely displaces the acids from the interstices of the nitro-cellulose, the line of separation between the acids and the water being fairly sharply defined throughout. The flow of water is continued until that issuing at the bottom is found to be free from all trace of acid. The purification of the nitro-cellulose is then proceeded with as usual, either in the same vessel or another. In the process above described, the object of the intro- duction of a small layer of sulphuric acid is mainly to prevent the fuming which would otherwise take place, and is not essential, as it is found it can be omitted without any deleterious effect. In order to use the mixed acids in the most economical manner, the waste acid from a previous operation may be used for a first nitration of the cellulose ; being afterwards displaced with fresh acids which carry the nitration to the required degree before they are in turn displaced by water. The apparatus may be used merely for the removal of the acid, in which case the nitration is carried out in other vessels in the usual way, and the nitro- cellulose removed to the displacement apparatus where it is just covered with waste acid, and the displacement then
MOULDING AND COMPRESSING GUN-COTTON. 77
proceeded with as above described. In some cases the process is carried out in an ordinary nitrating centrifugal, using the latter to effect preliminary drying after acid extraction. This gives a great advantage over the usual method of working ordinary centrifugal nitrating apparatus, because the acid being removed before the centrifugal is run, practically all danger of firing therein disappears, and a greater proportion of the waste acid is recovered.
In some cases the acids and water may be supplied by perforated pipes, lying along the edges of the nitrating vessel, and these edges may, if desired, be themselves made inclined, like the sides of the troughs f. In the case of effecting nitration in centrifugals as above, the displacing sulphuric acid and water may thus be supplied round the edges of the machines, or removal troughs such as /"may be used. It will be obvious that any inert liquid of suitable specific gravity may be used instead of sulphuric acid, as a separation layer.
Moulding. — By means of the small measuring tank above referred to, the gun-cotton pulp is drawn off from the stuff chest, and run into moulds of the shapes and sizes required. Thence a large proportion of the water is drawn off by means of tubes connected with the vacuum engine, the moulds having bottoms of fine wire gauze, in order to prevent the pulp from passing through. Hydraulic pressure of about 34 lbs. on the square inch is then applied, which has the effect of compressing the pulp into a state in which it has sufficient consistency to enable it to be handled with care, and also expels a portion of the remaining water.
Compressing. — The moulded gun-cotton is now taken to the press house, which is situated at some distance from the rest of the factory. Here the moulds are subjected to powerful hydraulic pressure, from 5 to 6 tons per square inch, and is compressed to one-third of its previous bulk. The slabs or discs thus formed are kept under pressure for a short time, not exceeding a minute and a half, to give the
78 NITRO-EXPLOSIVES.
requisite density. It should, when removed, be compact, and just sink in water, and should perceptibly yield to the pressure of the ringers. There are perforations in the press blocks, to allow of the escape of gases, if formed, by reason of sufficient heat being generated. The men working the press are placed under cover, behind strong rope mantlets having eye tubes which command a view of the press.
Packing. — The finished slabs and discs are dipped into a solution of soda and carbolic acid, and packed in special wood metal-lined cases. When it is to be sent abroad, the metal lining, which is made of tinned copper, is soldered down, but both the outer wooden and inner metal cases are fitted with air-tight screw-plugs, so that when necessary water can be added without unfastening the cases.
Reworked gun-cotton does not make such good discs as new pulped gun-cotton, probably because the fibrous tenacity of the gun-cotton has been destroyed by the amount of pressure it has previously undergone, so that when repulped it resembles fine dust, and a long time is required to press it into any prescribed form. It is generally boiled for eight hours to open up the fibre and remove alkali, then broken up by hand with wooden mallets, pulped, and then used with fresh gun-cotton in the pro- portion of i to 5 parts.
Manufacture at Le Bouchet. — At Le Bouchet gun- cotton was made thus : — 200 grms. of cotton were steeped for an hour in 2 litres of a mixture of 1 volume concentrated nitric and 2 volumes sulphuric acid. The cotton was then removed and pressed, whereby Y^ths of the waste acids was recovered. After this it was washed for one to one and a half hours in running water, strongly pressed again ; allowed to lie for twenty-four hours in wood-ash lye ; then well washed in running water ; pressed, and finally dried on a wide linen sheet, through which was forced air heated to 60 ° C. The average yield from 100 parts of cotton was
GRANULATION OF GUN-COTTON. 79
165 parts of gun-cotton. The strong' pressings of the gun- cotton, while still impregnated with acids, caused sub- sequent washings to be difficult and laborious.
Granulation of Gun-Cotton. — Gun-cotton is often required in the granulated form for use either alone or with some form of smokeless powder. This is done under the patent of Sir Frederick Abel in the following manner : — The gun-cotton from the poacher is placed in a centrifugal machine, very similar to the hydro-extractors before men- tioned, and used for wringing out the acids. In this machine it loses water until it only contains 33 per cent., and is at the same time reduced to a more or less fibrous state. It is then taken to the granulating room, where it is first passed through sieves or perforations, which break up the mass into little pieces like shot. The material is then transferred to a revolving drum made of wood or stout leather, which is kept constantly revolving for some time. The material is occasionally sprinkled with water. The drum in turning, of course, carries the granules partially round with it, but the action of gravity causes them to descend constantly to the lowest point, and thus to roll over one another continually. The speed of the drum must not be too rapid. None of the granules must be carried round by centrifugal force, but it must be fast enough' to carry them some little distance up the side of the drum. After removal from the drum the granules are dried upon shelves in the drying house.
Gun-cotton is also dissolved in acetone or acetic ether until it has taken the form of a jelly. It is then rolled into thin sheets, and when dry cut up into little squares. In the manufacture of smokeless powders from nitro-cellulose, nitro-lignine, &c, the various substances are mixed with the gun-cotton or collodion-cotton before granulating.
Collodion-Cotton. — In the manufacture of collodion or soluble cotton the finer qualities of cotton-waste are used
80 NITRO-EXPLOSIVES.
and the acids used in the dipping tanks are much weaker. The manufacture of collodion-cotton has become of more importance than gun-cotton, by reason of its use for the manufacture of the various forms of gelatine, such as gelatine dynamite, gelignite, forcite, &c, and also on account of its extensive use in the manufacture of many of the smokeless powders. It is also used for the manufacture of " collodion," which is a solution of collodion-cotton in ether-alcohol ; for the preparation of celluloid, and many other purposes. It is less explosive than gun-cotton, and consists of the lower nitrates of cellulose. It is soluble in nitro-glycerine, and in a mixture of 2 parts of ether and 1 of alcohol ; also in acetone, acetic ether, and other solvents. MM. Menard and Domonte were the first to prepare a soluble gun-cotton, and its investigation was carried on by Bechamp, who showed that its properties and composition were different to those of gun-cotton.
Manufacture. — The cotton used is cotton-waste.* It is thought by some that Egyptian cotton is preferable, and especially long fibre varieties. The strength of the acids used is, however, of more importance than the quality of the cotton. The percentage composition of the acid mixture which gives the best results is as follows : — Nitric acid, 23 per cent. ; sulphuric acid, 66 per cent. ; and water, 11 per cent.; and has a specific gravity of 1.7 12 (about). It can be made by mixing sulphuric acid of specific gravity 1.84 with nitric acid of specific gravity 1.368 in the pro- portions of 66 per cent, and 34 per cent, respectively. (The production of the penta-nitro-cellulose is aimed at if the collodion-cotton is for use as an explosive.) If the acids are much weaker than this, or potassium nitrate and sulphuric acid is used, the lower nitrates will be formed. The product, while being entirely soluble in ether-alcohol or nitro-glycerine, will have a low nitrogen content, whereas
* Raw cotton is often used.
COLLODION-COTTON. Si
a material with as high a nitrogen as 12 or 12.6 is to be aimed at.
The cotton should not be allowed to remain in the dipping tanks for more than five minutes, and the acid mixture should be kept at a temperature of 28° C. or thereabouts ; and the cotton should be removed after a few minutes, and should not be pressed out, as in the case of gun-cotton, but at once transferred to the pots and allowed to steep for forty-eight hours. (Some prefer twenty-four hours, but there is more chance in this case of the product containing non-nitrated cellulose.) When the nitration is complete, the collodion-cotton is removed from the pots, and treated in exactly the same manner as described under gun-cotton. The produce should be entirely soluble in ether-alcohol and nitro-glycerine, and contain as near 12.7 per cent, of nitrogen as possible. The theoretical nitrogen is for the penta-nitro-cellulose 12.75 Per cent. This will, however, seldom if ever be obtained. The following are some of the results I have obtained from different samples : —
Nitrogen.
|
(1.) |
(2.) |
(3.) |
|
|
German make |
- 11.64 |
11.48 |
11.49 Per cent. |
|
Stowmarket - |
- 12.57 |
12.60 |
11.22 „ |
|
Walsrode |
11. 61 |
12.07 |
H-99 |
|
Faversham |
- 12.14 |
1 1.70 |
11.60 „ |
and the following was the analysis of a sample (No. 1) of German-made collodion -cotton, which made very good blasting gelatine : —
Soluble cotton (collodion) 99.118 per cent. ) =n 6 cent
Gun-cotton - - - 0.642 „ J Non-nitrated cotton ■ 0.240 „ Total ash - - - 0.25 „
It should contain as little non-nitrated or unconverted cotton and as little gun-cotton as possible, as they are both insoluble in nitro-glycerol. The quality and composition of any sample of collodion-cotton can be quickly inferred
F
§2 NITRO-EXPLOSIVES
by determining the percentage of nitrogen by means of the nitrometer and the use of the solubility test* A high nitrogen content coupled with a high solubility is the end to be aimed at ; a high nitrogen with a low solubility shows the presence of gun-cotton, and a low nitrogen, together with a low solubility, the presence of unnitrated cotton. Where complete solubility is essential and the percentage of nitrogen less important, Dr Lunge recommends nitra- tion with a mixture of equal parts of sulphuric and nitric acids containing from 19 to 20 per cent, of water.
Mr T. R. France claims to have invented some im- provements in the manufacture of soluble nitro-cellulose. His object has been to produce an article as uniform as possible. His explanation of the imperfect action of the acids is that, however uniform the mixed acids may be in strength and proportions, and however carefully the opera- tions of nitrating, &c, may be conducted, there are variable elements found in different samples of cotton. The cotton fibre has for its protection a glazed surface. It is tubular and cellular in structure, and contains a natural semi-fluid substance composed of oil or gum, which varies in nature according to the nature of the soil upon which the cotton is grown. The tubes of the fibre seem to be open at one end only when the fibre is of normal length. When, therefore, the cotton is subjected to the action of the mixed acids, the line of least resistance seems to be taken by them, viz., the^ insides of the tubes constituting the fibre of the cotton, into which they are taken by capillary attraction, and are subject to change as they progress, and to the increased resistance from the oil or gum, &c, in their progress, and therefore to modified action, the result of which is slower and slower action, or chemical change. He also thinks it is possible that the power of capillary attraction is balanced in the tubes by air contained therein, after a little, sufficiently so to prevent the acids from taking full effect. To get over
* See Analysis of Explosives.
NITRATED GUX-COTTOX. 83
this, Mr France uses his cotton in a fine state, almost dust, in fact, and then nitrates in the usual mixture of acids at 400 to 90° F., the excess of acids being removed by pressure. He says he does not find it necessary to wash this fine cotton dust in an alkaline solution previous to nitration. His mixed acids consist of 8 parts HN03 = 42° B., and 12 parts H.2S04 = 66° B., and he stirs in the dipping tank for fifteen minutes, the temperature being 50° F. to ioo° F., the temperature preferred being 75° F.
" Nitrated " Gun-Cotton. — The nitrates that are or have been mixed with gun-cotton in order to supply oxygen are potassium nitrate, ammonium nitrate, and barium nitrate (tonite). The total combustion of gun- cotton by potassium nitrate corresponds to the equation : —
io[C24H18(N03H)1109] + 82KN03=i99C02+4iK2C03
+ 145^0 + 96X0,
or 828 grms. of nitrate for 1,143 grrns. of gun-cotton, or 42 per cent, nitrate and 58 per cent, gun-cotton. The explosive made at Faversham by the Cotton Powder Company, and known as tonite No. 1, consists of very nearly half gun-cotton and half barium nitrate. The relations by weight of total combustion would be 51.6 of gun-cotton to 48.4 of barium nitrate. The average com- position of tonite I have found by analysis to be 51 per cent, gun-cotton to 49 per cent, barium nitrate. The heat liberated is practically the same as for an equivalent weight of KNOo ; but the barium nitrate mixture weighs 2,223 grms. instead of 1,971 grms., or one-eighth more. The advantage in mixing a nitrate with gun-cotton is that it supplies oxygen, and by converting all the carbon into carbonic acid, prevents the formation of the poisonous gas carbonic oxide (CO J. The nitrates of potassium and barium are also used admixed with nitro-cellulose in several of the sporting smokeless powders.
84 NITRO-EXPLOSIVES.
The Manufacture of Tonite. — The explosive tonite was patented by Messrs Trench, Faure, and Mackie, and is manufactured at Faversham and Melling at the works of the Cotton Powder Company, and at San Francisco by the Tonite Powder Company. It consists of finely divided and macerated gun-cotton incorporated with finely ground nitrate of barium which has been carefully recrystallised. It is made by acting upon carbonate of barium* with nitric acid. The wet and perfectly purified, finely pulped gun- cotton is intimately mixed up between edge runners with about the same weight of nitrate, and the mixing and grinding continued until the whole has become an intimately mixed paste. This paste is then compressed into cartridges, formed with a recess at one end for the purpose of inserting the detonator. The whole is then covered with paraffined paper.
The tonite No. 2 consisted of gun-cotton, nitrates of potash and soda, charcoal and sulphur. Tonite No. 3 7 is composed as follows : — Gun-cotton, 19 per cent. ; di-nitro- benzol, 13 per cent. ; and barium nitrate, 68 per cent, or similar proportions. It is a yellowish colour, and being slower in its explosive action, is better adapted for blasting soft rock.
Tonite is extensively used in torpedoes and for sub- marine blasting, also for quarries, &c. Large quantities were used in the construction of the Manchester Ship Canah Among its advantages are, that the English railways will take~tonite on the same footing as gunpowder ; it is a very dense material ; if wetted it can easily be dried in the sun ; it very readily explodes by the use of a proper detonator ; while it burns very slowly and without the least danger ; the cartridges being waterproofed, it can be employed in wet bore holes, and it can be tamped with water ; and
* Witherite, BaCOs + ,HN03 = Ba(N03)., + CO,+ HX>. t Tonite No. 1 was patented by Messrs Trench, Faure, and Mackie, and tonite Nos. 2 and 3 by Trench alone.
DANGERS WITH GUN-COTTON. 85
finally, as it contains sufficient oxygen to oxidise the carbon, no carbonic oxide (CO) gas is formed, i.e., its detonation is perfect. It is a very safe explosive to use, being little susceptible to either blows or friction.
Not long ago, a committee, composed of Prof. P. Bedson, Drs Drummond and Hume, Mr T. Bell, one of H.M. Inspectors of Coal Mines, and others, in considering the problem whether the fumes produced by the combustion of tonite were injurious to health, carried out a series of experiments in coal mines for this purpose. The air at the "intake" was analysed, also the air of the "return," and the smoky air in the vicinity of the shot holes. The cartridge was surrounded by the flame-extinguishing mix- ture, and packed in a brown paper bag. During the first experiment nineteen shots were fired ( = 6.29 lbs. tonite). The " return " air showed only a trace of carbonic oxide gas (CO). At the second experiment thirteen shots were fired ( = 4.40 lbs. tonite), and analysis of the air of the "return " showed that CO was present in traces only, whilst the fumes contained only 1.9 to 4.8 parts per 10,000.
Dangers in connection with the Manufacture of Gun- cotton, &c — Of all the nitro compounds, the least dangerous to manufacture are gun-cotton and collodion-cotton. The fact that the Stowmarket Factor)- is within five minutes' walk of the town shows how safe the manufacture of this explosive is regarded. With the exception of the nitration and the compression into blocks or discs, the whole process is worked with a large excess of water, and the probability of an explosion is thus reduced to a minimum. Among the precautions that should, however, be taken, are— first, the careful extraction of the resinous and soluble substances from the cotton before nitration, as it was shown many years ago by Sir F. A. Abel that the instability of the gun- cotton first manufactured in England and Austria was chiefly due to these compounds. The)- are generally re- moved by boiling the cotton in a soda solution.
86 NITRO-EXPLOSIVES.
The actual nitration of cotton is not a dangerous operation, but the operations of wringing in the hydro- extractors, and washing the nitro-cotton after it leaves the first centrifugal machine, are somewhat so. Great care should be taken that the wrung-out nitro-cotton at once comes in contact with a large excess of water, i.e., is at once immersed entirely in the water, since at this stage it is especially liable to decomposition, which, once started, is very difficult to stop. The warmer the mixture and the less water it contains, the more liable it is to decomposition ; hence it is that on warm and damp days the centrifugal machines are most likely to fire. The commencement of decomposition may be at once detected by the evolution of red fumes. Directly the gun-cotton is immersed in the large quantity of water in the beater and poacher it is safe.
In order that the final product may be stable and have good keeping qualities, it is necessary that it should be washed completely free from acid. The treatment in the beater and poacher, by causing the material to assume the state of a fine pulp, in contact with a large quantity of water, does a good deal to get rid of the free acid, but the boiling process is absolutely necessary. It has been pro- posed to neutralise the free acid with a dilute solution of ammonia ; and Dr C. O. Weber has published some experi- ments bearing upon this treatment. He found that after treatment with ammonia, pyroxyline assumed a slightly yellowish tinge, which was a sure sign of alkalinity. It was then removed from the water, and roughly dried between folds of filter paper, and afterwards dried in an oven at yo° C. After three hours, however, an explosion took place, which entirely destroyed the strong copper oven in which the nitro-cotton (about one oz.) had been drying. The explosion was in some respects remarkable. The pyroxyline was the di-nitro-cellulose (or possibly the penta-nitro ?), and the temperature was below the igniting point of this material (40° C. would have been a better temperature). Dr Weber determined the ignition point of
DANGERS WITH GUN-COTTON. 87
his di-nitro-cellulose, and found it to be 1940 to 198° C, and he is therefore of opinion that the explosion was due to the treatment of the partially washed material with ammonia. A certain quantity of ammonium nitrate was probably formed, and subsequently dried upon the nitro- cellulose, in a state of very fine subdivision. The faintest trace of acid would then be sufficient to bring about the explosive ignition of the ammonium nitrate.
The drying of gun-cotton or collodion-cotton is also a somewhat dangerous operation. A temperature of 400 C. (1040 F.) should not be exceeded, and thermometers should be placed in the nitro-cotton, and the temperature frequently observed. An electric alarm thermometer is also a useful adjunct to the cotton drying house. Great care must also be taken that there are no exposed hot- water pipes or stoves in the drying house, as the fine gun- cotton dust produced by the turning or moving of the material upon the shelves would settle upon such pipes or stoves, and becoming hot, would be very sensitive to the least friction. The floor also should be covered with linoleum or indiarubber. When hot currents of air are made to pass over the surface of gun-cotton, the gun-cotton becomes electrified. It is important, therefore, to provide some means to carry it away. Mr W. F. Reid, F.I.C., was the first to use metal frames, carriers, and sieves, upon which is secured the cloth holding the gun-cotton, and to earth them.
The compression of gun-cotton into blocks, discs, &c, is also attended with considerable risk. Mr O. Guttmann, in an interesting paper upon " The Dangers in the Manu- facture of Explosives " (/our. Soc. Chem. Ind., No. 3, vol. xi., 1892), says: "The compression of gun-cotton into cartridges requires far more care than that of gunpowder, as this is done in a warm state, and gun-cotton even when cold, is more sensitive than gunpowder. When coming out of the centrifugal machines, the gun-cotton should always pass first through a sieve, in order to detect nails
88 NITRO-EXPLOSIVES.
or matches which may by chance have got into it. What has been said as to gunpowder presses applies still more to those for gun-cotton, although the latter are always hydraulic presses. Generally the pistons fit the mould per- fectly, that is to say, they make aspiration like the piston of a pump. But there is no metal as yet known which for any length of time will stand the constant friction of com- pression, and after some time the mould will be wider in that part where the greatest compression takes place. The best metal for this purpose has proved to be a special steel made by Krupp, but this also is only relatively better ; for pistons I prefer hard cast iron. If the position of the moulds and pistons is not exactly the same in all cases, what the Germans call ' Ecken ' (English 'binding') will take place, viz., the mould will stand obliquely to the piston, and a dangerous friction will result." " Of course, it is necessary to protect the man working the hydraulic valves during compression. At Waltham Abbey they have a curtain made of ship's hawsers, which is at the same time elastic and resistant." Mr Guttmann has found that a partition wall 12 inches thick, made of 2-inch planks, and filled with ground cinders, gives very effective protection. A door in this partition enables the workman to get to the press, and a conical tube penetrates the wall, enabling the man to see the whole work from a safe standpoint. The roof, or one side of the building, should be of glass, so as to give the explosion a direction.
Trench's Fire-extinguishing Compound is manu- factured by the Cotton Powder Company at Faversham, and is the invention of Mr George Trench, F.C.S., the manager of the Company. The object of the invention is to surround the cartridges of tonite, when used in coal mines, with a fire-extinguishing compound. If a charge of tonite, dynamite, or gelatine dynamite is put inside a few ounces of this mixture, and then fired, not the least trace of flame can be observed, and experiments appear to show
FIRE-EXTINGUISHING COMPOUND.
89
that there is no flame at all. The compound consists of sawdust impregnated with a mixture of alum and chlorides of sodium and ammonia. Fig. 22 shows the manner of placing the tonite cartridge in the paper bag, and surround- ing it with the fire-extinguishing compound, a a. The attachment of the fuse and detonator is also shown.
The following report (taken from the Faversham News, 22nd Oct. 1887) of experiments conducted in the presence of several scientific and mining men will show its value : — " A large wrought-iron tank, of 45 cubic feet capacity, had been sunk level with the ground in the middle of the yard ;
CAPW^'fiE l°7r0Mro-!
PAPER CASE FOP CARTRIDGE
Fig. 22. — Trench's Fire-Extinguishing Cartridge.
to this tank the gas had been laid on, for a purpose that will be explained later on. The charges were fired by means of electricity, a small dynamo firing machine being placed from 30 to 40 yards away from the ' mine.' " Opera- tions were commenced by the top of the tank being covered over and plastered down in order to make it air-tight ; then a sufficient quantity of coal gas was placed in it to make it highly inflammable and explosive, the quantity being ascer- tained by a meter which had been fixed specially for the purpose. Whilst the gas was being injected the cartridge was prepared.
The first experiment was to try whether a small charge of tonite — fired without the patent extinguisher — would ignite the gas. The gas having been turned on, a miner's lamp was placed in the " tank," but this was extinguished before the full quantity of gas had gone through the meter. However, the gas being in, the charge of 1^ oz. tonite was
go NITRO-EXPLOSIVES.
placed in the " mine," the detonator was connected by means of long wires to the dynamo machine, and the word was given to " fire." With a tremendous report, and a flash of fire, the covering of the mine flew in all directions, clearly showing that the gas had exploded. The next cartridge (a similar charge) was prepared with the patent compound. First of all a brown paper case of about 2 inches diameter was taken, and one of the tonite cartridges was placed in the centre of it, the intervening space between the charge and the case being packed with the " fire-extinguishing compound." The mine having had another supply of gas injected, the protected cartridge was placed inside and fired. The result was astonishing, the explosion not being nearly so loud, whilst there was not the least flash of fire. " Protected " and " unprotected " charges were fired at intervals, gas being turned into the tank on each occasion. Charges of tonite varying from 1 to 6 oz. were also used with the compound. The report was trifling, whilst no flash could be seen.
Uses of Collodion-Cotton. — The collodion or soluble gun-cotton is used for a variety of purposes. The chief use is, however, for the manufacture of the various explosive gelatine compounds, of which blasting gelatine is the type. It is also very extensively used in the manufacture of smokeless powders, both military and sporting — in fact, very few of them do not contain it. In some, however, nitro-lignose or nitrated wood is used instead. This, how- ever, is chemically the same thing, viz., nitro-cellulose, the cellulose being derived from the wood fibre. It is more used in this connection than the higher nitrate gun-cotton. Another use to which it has been applied very extensively, of recent years, is in the manufacture of " celluloid." It is used in photography for the preparation of the films on the sensitised plates, and many other purposes. Dissolved in a solution of two parts ether and one of alcohol, it forms the solution known as collodion, used for a variety of
CELLULOID. 91
purposes, such as a varnish, as a paint for signals ; in surgery, for uniting the edges of wounds.
Quite lately, Mr Alfred Nobel, the well-known inventor of dynamite, has patented the use of nitro-cellulose, hydro- or oxy-cellulose, as an artificial substitute for incliarubber. For this purpose it is dissolved in a suitable non-volatile or slightly volatile " solvent," such as nitro-naphthalene, cli- nitro-benzene, nitro-toluene, or its homologues ; products are obtained varying from a gelatinous consistency to the hardness of ebonite. The proportions will vary from about 20 per cent, of nitro-cellulose in the finished product, form- ing a soft rubber, to 50 per cent, nitrating celluloid, and the "solvent" chosen will depend on the use to which the rubber substitute is to be put, the liquids giving a more elastic substance, whilst mixtures of solids and liquids may be employed when the product is to be used at high tem- peratures. By means of rollers steam heated, the incor- poration may be accomplished without the aid of a volatile liquid, or the nitro-cellulose may be employed wet, the water being removed after " solution."
It is advisable to use the cellulose nitrated only just enough to render it suitable, in order to reduce the inflammability of the finished product. Mr W. Allen, M.P., of Gateshead, proposed to use celluloid for cartridge cases, and thus to lighten ammunition, and prevent jamb- ing, for the case will be resolved into gases along with the powder. Extractors will also be done away with.
Celluloid is an intimate mechanical mixture of pyr- oxyline (gun-cotton or collodion-cotton) with camphor, first made by Hyatt, of Newark, U.S.A., and obtained by adding the pyroxyline to melted camphor, or by strongly com- pressing the two substances together, or by dissolving the constituents in an appropriate solvent, e.g., alcohol or ether, and evaporating to dryness. A combination of the two latter methods, i.e., partial solution, with pressure, is now usually adapted. The pyroxyline employed is generally the tetra-
92 NITRO-EXrLOSIVES.
and penta-nitrated cellulose, the hexa-nitrate (gun-cotton) being but seldom used on account of its explosive properties.
Care is taken to prevent the formation of the hexa- nitrate by immersing the cellulose in only moderately strong nitric acid, or in a warm mixture of nitric and sulphuric acids. The paper, either in small pieces or in sheets, is immersed for about twenty-five minutes in a mixture of 2 parts of nitric acid and 5 parts of sulphuric acid, at a temperature of about 30°C, after which the nitrated cellulose is thoroughly washed with water to remove the last traces of free acid, pressed, and whilst still moist, mixed with the camphor.
In the process of Trebouillet and De Besancele, the cellulose, which may be in the form of paper, cotton, or linen, is twice nitrated — first in the acid mixture employed in a previous operation ; and secondly, in a fresh mixture of 3 parts sulphuric acid of 1.83 specific gravity, and 2 parts concentrated nitric acid containing nitrous acid. After each nitration the mass is subjected to pressure, and is then carefully washed with water, to which, at the last, a small quantity of ammonia or caustic soda is added to remove the final traces of acid. The impregnation of the pyroxyline with the camphor is effected in a variety of ways.
The usual proportion of the constituents is 2 parts pyroxyline and 1 part camphor. In Trebouillet and De Besancele's process, 100 parts of pyroxyline are intimately mixed with from 40 to 50 parts camphor, and moulded together by strong pressure in a hot press, and afterwards dried by exposure to air, desiccated by calcium chloride or sulphuric acid. The usual method is, however, to dissolve the camphor in the least possible quantity of alcohol, and sprinkle the solution over the dry pyroxyline, which is then covered with a second layer of pyroxyline, and the whole again treated with the camphor solution, the addition of pyroxyline and camphor solution being repeated alternately until the requisite amount of celluloid mixture is obtained.
The mass, which sinks together in transparent lumps, is
CELLULOID. 93
worked for about an hour between cold iron rollers, and then for the same period between rollers which can be gently heated by steam. The layer of celluloid surround- ing the rollers is then cut away and again pressed, the resulting cake, which is now about i cm. thick, being cut into plates of about yo cm. long and 30 cm. broad. These are placed one above the other, and strongly pressed together by hydraulic pressure at a temperature of about yoJ for twenty-four hours. The thick cakes are once more cut into plates of the desired thickness, and placed in a chamber heated from 300 to 40° for eight to fourteen days, whereby they become thoroughly dry, and are readily made into various articles either by being moulded while warm under pressure, cut, or turned. Occasionally other liquids, e.g., ether and wood spirit, are used in place of alcohol as solvents for the camphor.
Celluloid readily colours, and can be marbled for manufacturing purposes, &c. It is highly inflammable and not explosive even under pressure, and may be worked under the hammer or between rollers without risk. It softens in boiling water, and may be moulded or pressed. Its specific gravity varies slightly with its composition and with the degree of pressure it has received. It is usually 1.35. It appears to be merely a mixture of its components, since by treatment with appropriate solvents the camphor may be readily extracted, and on heating the pyroxyline burns away while the camphor volatilises.
The manufacture of pyroxyline for the purpose of making celluloid has very much increased during recent years, and with this increase of production improved methods of manufacture have been invented. A series of interesting papers upon the manufacture of pyroxyline has been published by Mr Walter D. Field, of New York, in the Journal of the American Chemical Society* from which the following particulars are taken : —
* Vol. xv., No. 3, 1S93 ; Vol. xvi., No. 7, 1894 ; Vol. xvi., No. 8, 1894. Figs. 19, 20, 21, 22, and 23 are taken from Mr Field's paper.
94 NITRO-EXPLOSIVES.
Selection of the Fibre. — Cotton fibre, wood fibre, and flax fibre in the form of raw cotton, scoured cotton, paper, and rags are most generally used, and give the best results. As the fibres differ greatly in their structure, they require different methods of nitrating. The cotton fibre is a flattened hollow ribbon or collapsed cylindrical tube, twisted a number of times, and closed at one end to form a point. The central canal is large, and runs nearly to the apex of the fibre. Its side walls are membraneous, and are readily penetrated by the mixed acids, and conse- quently the highest nitration results. In the flax fibre the walls are comparatively thick, the central canal small ; hence it is to be presumed that the nitration must proceed more slowly than in the case of cotton. The New Zealand flax gives the most perfectly soluble nitrates of any of the flaxes. Cotton gives a glutinous collodion, and calico a fluid collodion. One of the largest manufacturers of pyroxyline in the States uses the "Memphis Star" brand of cotton. This is an upland cotton, and its fibres are very soft, moist, and elastic. Its colour is light creamy white, and is retained after nitration. The staple is short, and the twist inferior to other grades, the straight ribbon-like filaments being quite numerous. This cotton is used carded, but not scoured. This brand of cotton contains a large quantity of half and three-quarter ripe fibre, which is extremely thin and transparent, distributed throughout the bulk of the cotton (Monie., Cotton Fibre, 6j). Mr Field says, " This is a significant fact when it is known that from this cotton an extremely soluble pyroxyline can be produced."
Pyroxyline of an inferior grade as regards colour only can be produced from the cotton wastes of the trade. They must be scoured before they are fit for nitrating. Paper made from the pulps of sulphite and sulphate processes is capable of yielding a very soluble pyroxyline. It can be nitrated at high temperatures and still yield good results. Tissue paper made from flax fibre is also used after being cut into squares.
NITRATION OF FIBRE. 95
Mowbray (U.S. P., No. 443, 105, 3rd December 1890) says that a pure cotton tissue paper less than -^ inch in thickness, thin as it is, takes on a glutinous or colloid surface, and thus requires some thirty minutes to enable the nitration to take place. With a thicker paper only the surface would be nitrated. He therefore uses a fibre that has been saturated with a solution of nitrate of soda, and afterwards dried slowly, claiming that the salt crystallises in the fibre, or enters by the action termed osmose, and opens up the fibre to the action of the acid. This process would only be useful when the cotton is to be nitrated at a low temperature. At a high temperature it would be unnecessary.
Dietz and Wayne (U.S. P., No. 133, 969) use ramie, rheca, or China grass for producing a soluble pyroxyline. That made from ramie is always of uniform strength and solubility, and requires a smaller quantity of solvent to dissolve it than that made from cotton. Mr Field's experience, however, is entirely contrary to this statement. Such is the influence of the physical form of the fibre on the process of nitration, that when flax fibre and cotton fibre are nitrated with acid mixtures of exactly the same strength, and at the same temperature, the solution of the first is glutinous or thick, and the second fluid or thin. By simply nitrating at a higher temperature than the cotton, the flax will yield a pyroxyline giving an equally fluid collodion.
The presence of chlorine in the fibre must be carefully avoided, as such a fibre will yield an acid product which cannot be washed neutral. The fibre must be dry before nitration ; and this is best done, according to Mr Field, by using the form of drier used in drying wool.
Nitration of the Fibre. — Mixed cotton and flax fibre in the form of paper, from TTfo 0 to xwir inch thick, and cut into 1 -inch squares, is nitrated by the Celluloid Manufac- turing Company, and the same paper, left in long strips,
96
NlTRO-EXPLOSlVES.
I inch wide, is used for nitration by the Xylonite Manu- facturing Company, of North Adams, Mass. (U.S.A.).
The Celluloid Company introduce the cut paper into the mixed acids by means of a hollow, rapidly revolving tube, flared at the lower end, and immersed in the mixed acids. The centrifugal force of the revolving tube throws the paper towards the sides of the vessel, leaving the centre of the vessel ready for fresh paper.
The Xylonite Company simply cut the paper into long strips, and introduce it into the mixed acids by means of forks. The arrangement used by this Company for holding the mixed acids is a cylindrical vessel divided into a number of sections, the whole revolving like a turntable, thus allowing the workman to nitrate successively each lot of paper at a given point. This Company did not remove the acid from the paper after its immersion, but plunged it immediately into the water, thus losing a large proportion of the waste acid. The Celluloid Company, by using the paper in smaller pieces, and more paper to a pound of acid, and wringing the mixed acid from the paper before immer- sion in water, had a better process of nitration.
Other manufacturers use earthenware vessels, and glass or steel rods, hooked at one end, having small pieces of
rubber hose pulled over the other end to prevent the hand from slipping. The form of vessel in general use is that given in Fig. 23. It is large enough to nitrate 1 lb. of cotton at a time. The hook at one end of the rod enables the workman to pull the pyroxyline apart, and thus en- sures saturation of the fibre. In the winter the room in which the nitrating is done must be kept at a temperature of about 70° F. in order to secure equality in the batches.
The nitrating apparatus of White and Schupphaus (U.S. P., No. 418, 237, 89) Mr Field considers to be both novel and excellent. The cage (Fig. 24), with its central
Fig. 23. — Vessel for Nitrating Cotton or Pafek.
CELLULOID — APPARATUS USED.
97
perforated cylinder (Fig. 25), is intended to ensure the rapid and perfect saturation of the tissue paper used for nitrating. The patentees say that no stirring is required with their apparatus. This, says Mr Field, might be true when paper is used, or even cotton, when the temperature
i
1
f
Fig. 24. — Central Perforated Fig. 25. — The Cage.
Cylinder. White and Schupphaus' Nitrating Apparatus.
of nitration is from 30° to 35 " C, but would not be true if the temperature were raised to 50° to 55' C. The process is as follows : — The paper is nitrated in the cage (Fig. 25), the bottom of which is formed by the flanged plate C, fastened
Fig.
-Celluloid Nitrating Pot.
Fig. 27. — Another View.
to the bottom of the internal cylinder B. After nitration the cage is carried to a wringer, which forms the basket, and the acids removed. Finally, the cage is taken to a plunge tank, where the paper is removed from the cage by simply pulling out the central perforated cylinder B. Fig.
G
98
NITRO-EXPLOSIVES.
26 shows the nitrating pot, with its automatic cover. The plunge tank is shown in plan and section in Figs. 28 and 29. This apparatus is suitable for the nitration of cotton fibre in bulk at high or low temperatures. Other methods that
Figs. 28, 29. — Plunge Tank, in Plan and Section.
have been patented are Mowbray's (U.S. P., No. 434, 287), in which it is proposed to nitrate paper in continuous lengths, and Hyatt's (U.S. P., No. 210, 611).
The Acid Mixture. — Various formulae have been pub- lished for producing soluble nitro-cellulose. In many instances, although the observations were correct for the single experiment, a dozen experiments would have pro- duced a dozen different products. The composition of the acids used depends upon the substance to be nitrated, and the temperature at which the nitration will be worked. Practically there are three formulae in general use — the one used by the celluloid manufacturers ; another in which the cotton is nitrated at high temperatures ; and a third in which the temperature of the immersion is low, and the time of nitration about six hours. Of the three, the best method is the last one, or the one in which the cotton is immersed at a low temperature, and then the reaction allowed to proceed in pots holding from 5 to 10 lbs. of cotton. The formula used by the celluloid manu- facturers for the production of the low form of nitrated product which they use is : —
ACID MIXTURE. 99
Sulphuric acid - - - - - 66 parts by weight.
Nitric acid - - - - - - 17 „ ,,
Water ------ 17 „ „
Temperature of immersion, 30' C. Time, twenty to thirty minutes.
The cellulose is used in the form of tissue paper T<y2<jo inch thick, 1 lb. to 100 of acid mixture. The nitro- cellulose produced by this formula is very insoluble in the compound ethers and other solvents of pyroxyline, and is seemingly only converted or gelatinised by the action of the solvent. The next formula produces a mixture of tetra- and penta-nitro-celluloses hardly soluble in methyl- alcohol (free from acetone), but very soluble in anhydrous compound ethers, ketones, and aldehydes : —
Nitric acid, sp. gr. 1.435 ----- 8 lbs.
Sulphuric acid, sp. gr. 1.83 - - - 15! ,,
Cotton - - - - - - - - 14 oz.
Temperature of nitration, 6o° C. Time of immersion, forty-five minutes.
The 6o° of temperature is developed by mixing the acids together. The cotton is allowed to remain in the acid until it feels " short " to the rod.
The following table, due to Mr W. D. Field, shows very plainly the great variation in the time of the immer- sion and the temperature by seemingly very slight causes. It extends over fourteen working days, during which time it rained four days. The formula used is that given above, except that the specific gravity of the nitric acid is some- what lower. The product obtained differs only from that produced by using nitric acid of specific gravity 1.43 in being soluble in methyl-alcohol. From 30 to 35 lbs. of pyroxyline were produced in each of the fourteen days.
A careful examination of this table will prove very instructive. The increase in yield varies from 3 1 per cent, to nothing, and the loss runs as high as 10 per cent., yet care was taken to make the product uniform in quality. On the days it rained there was a loss, with the exception
100
NITRO-EXPLOSIVES.
of the fourth day, when there was neither a loss nor a gain. On the days it was partly clear, as just before or after rain, the table shows a loss in product. We can explain this fact by reason of the moisture-absorbing qualities of the cotton. On the rainy days it would absorb the moisture from the air until, when immersed in the acids, they were weakened, and the fibre dissolved more or less in weakened acid, producing what is known as " burning " in the batch.
Specific Gravity.
H,S04.
HNO,.
Time.
De^P(J. PercentaSe
Clear .
3. Cloudy
4. Rain
5. Clear
6. Rainy
7. Cloudy
8. Clear
9. Partly clear.
11. Cloudy
12. Rainy
13. Partly clear.
14. Cloudy
837
837
837
8377
8391
835
835
S24
83 832
822
8378
837
.4249
.4249
.4226
.420
.42
.422
.4226
.422
.4271
.4271
•425
•425
•4257
•4257
20 20
45 20
15 35 20
35 20 10 10 10 5o 56
40
35 620
10 6oJ
... 500
25 58°
5o 58°
20 58"
40 50°
40 50°
62°
620 620
630
62°
620
640
620
6o° 6o° 60° 6o°
580 6oQ
20 16
It will also be noticed that on days which show a loss, the time of the immersion was correspondingly short, as on the tenth, twelfth, and seventh days.
The lesson this table teaches is, that it is almost im- possible to nitrate cellulose in small quantities, and get uniform results, when the nitration is carried on at high temperatures. As regards the solubility of pyroxyline, Parks found that nitro-benzene, aniline, glacial acetic acid, and camphor, dissolved in the more volatile solvents methyl-alcohol and alcoho.-etner, were much the best solvents for producing a plastic, as they are less volatile,
ACID MIXTURE. TOI
and develop greater solvent action under the influence of heat. Nitro-benzene gives a solution that is granular ; it seems to merely convert the pyroxyline, and not to dissolve it ; but on the addition of alcohol, a solution is at once obtained, and the granular appearance disappears, and the solution becomes homogeneous. The acid mixture and the method of nitrating have much to do with the action of the various solvents, so also has the presence of water.
Dr Schupphaus found that propyl and isobutyl alcohols with camphor were active solvents, and the ketones, palmi- tone, and stearone in alcohol solution, also alpha- and beta- naphthol, with alcohol and anthraquinone (diphenylene diketone) in alcoholic solution, and also iso- valeric aldehyde and its derivatives, amyliden-dimethyl and amyliden-diethyl ethers.
August Sayer (U.S. P., No. 470, 451) finds diethyl-ketone, dibutyl-ketone, di-pentyl-ketone, and the mixed ketones,* methyl-ethyl, methyl-propyl, methyl-butyl, methyl-amyl, and ethyl-butyl ketones are active solvents of pyroxyline ; and Paget finds that although methyl-amyl oxide is a solvent, that ethyl-amyl oxide is not.
The solvents of pyroxyline can be divided into general classes — First, those which are solvents without the aid of heat or solution in alcohol ; second, those that are solvents when dissolved in alcohol. These solvents are those which also develop a solvent action when heated to their melting point in combination with pyroxyline.
Mr W. D. Field groups the solvents of pyroxyline into classes thus : Two of the monohydric alcohols ; compound
* Ketones are derived from the fatty acids by the substitution of the hydroxyl of the latter by a monad positive radical. They thus re- semble aldehydes in constitution. The best-known ketone is acetone CHy.CO.CHo. Mixed ketones are obtained by distilling to^ether salts of two different fatty acids. Thus potassic butyrate and potassic acetate form propyl-methyl-ketone —
/C(C2HS)H21
\CO.CH;1 J
102 NITRO-EXPLOSIVES.
ethers of the fatty acids with monohydric alcohols, alde- hydes ; simple and mixed ketones of the fatty acid series. These four classes include the greater number of the solvents of pyroxyline. Those not included are as follows : — Amyl-nitrate and nitrite, methylene- di-methyl ether, ethidene-cliethyl ether, amyl-chloracetate, nitro-benzeneand di-nitro-benzcne, coumarin, camphor, glacial acetic acid, and mono-, di-, and tri-acetin.
Richard Hale uses the following solvent : — Amyl- acetate, 4 volumes ; petroleum naphtha, 4 volumes ; methyl- alcohol, 2 volumes ; pyroxyline, 4 to 5 ounces to the gallon of solvent. Hale used petroleum naphtha to hasten the drying qualities of the varnish, so that it would set on the article to be varnished before it had a chance to run off. It is, however, the non-hygroscopic character of the solvent that makes the varnish successful. This formula is very largely used for the production of pyroxyline varnish, which is used for varnishing pens, pencils, &c, also brass-work and silver-ware.
The body known as oxy-cellulose* is formed by the action of nitric acid upon cellulose when boiled with it. The quantity formed is about 30 per cent, of cellulose acted upon. When washed free from acid, it gelatinises. It is then soluble in dilute alkalies, and can be reprecipitated from solution by alcohol, acids, or saline solutions. Messrs Cross and Bevan assign to it the formula ClgH2GO10. It dissolves in concentrated sulphuric acid, and with nitric acid forms a nitro body of the formula C1SH2301C3(N02), which is prepared as follows : — The gelatinous oxy-cellulose is washed with strong nitric acid until free from water, and is then diffused through a mixture of equal volumes of strong sulphuric and nitric acids, in which it quickly dissolves. The solution, after standing for about an hour, is poured in a fine stream into a large volume of water, by which the
* " On the Oxidation of Cellulose," by C. F. Cross and E. J. Bevan,
Jour. Chcm. Soc, 1883, p. 22.
NITRO-STARCH. 1 03
" nitro " body is precipitated as a white flocculent mass. The product, after drying at 110° C, was found upon analysis to contain 6.4S per cent, nitrogen.
Miscellaneous Nitro-Explosives.
Nitro-Starch. — It is only recently that, by means of the process introduced by the " Actiengesellschaft Dyna- mit Nobel," it has been possible to make this explosive upon the manufacturing scale. Nitro-starch has been known since 1883, when Braconnot discovered it, and called it xyloidine. Its formula is C(.Hs03(N03).2, but Dr Otto Miihlhausen has lately succeeded in preparing higher nitrated compounds, viz. : —
[a.) C6HH02j(N03)2j. {/>.) C6H?04(NOs)3.
Or doubling the molecule of starch : —
Nitrogen, i. Tetra-nitro-starch C12H16Oi;(ONO.,)4 - - - - 1 1. 1 1 per cent,
ii. Penta-nitro-starch CuJI1505(ONOo)rj - - - - 12.75
iii. Ilexa-nitro-starch C1oH1404(OiST0:>)(., - - - - 14.14 ,,
He regards them as true ethers (esters) of nitric acid. Thus on treatment with sulphuric acid, these compounds yield NO.,H, the residue O.N02 thus appearing to be re- placed by the sulphuric acid residue. On treatment with a solution of ferrous chloride, nitric oxide and ''soluble" starch are regenerated. On shaking with sulphuric acid over mercury, all the nitrogen is split off as XO.
Tetra-nitro-starch is prepared upon the large scale as follows : — A quantity of potato-starch is taken and exposed in some suitable desiccating apparatus at a temperature of ioo° C. until all the moisture which it contains is com- pletely driven off. It is then reduced to a fine powder by grinding, and dissolved in nitric acid of specific gravity 1. 501. The vessel in which this solution is accomplished is made of lead, and must be provided with two jackets, cooled by means of water. It should further be fitted with
104 NITRO-EXPLOSIVES.
a screw-agitator, in order to keep the nitric acid circulat- ing freely. The charge of starch is introduced through an opening in the cover of this digesting vessel, and the pro- portions of acid to starch are 10 kilogrammes of starch to ioo kilos, of acid. The temperature is kept within the limits 20° to 25° C. When the solution of the starch is. complete, the liquid is conducted into a precipitating ap- paratus, which is also provided with a cooling jacket, for the purpose of regulating the temperature. The bottom of this vessel is double and perforated, and here is placed a layer of gun-cotton to act as a filter. This vessel is filled with spent nitro -sulphuric acid obtained as a waste product from the nitro-glycerine manufactory, and the solution of starch in nitric acid is sprayed into it through an injector worked by compressed air, whereby the nitro-starch is thrown down in the form of a fine-grained powder}' precipitate.
In order to precipitate 100 kilos, of the acid solution of starch, it is necessary to employ 500 kilos, of spent nitro- sulphuric acid. As it is precipitated the nitro-starch collects on the gun-cotton filter, and the acid liquor is run off through a tap placed beneath the perforated double bottom of the vessel, and of course below the filter pad. The precipitated starch is further cleansed from acid by repeated washings and by pressure, until all trace of acidity has been eliminated, and the substance exhibits a neutral reaction. The next step is to treat the nitro-starch with a 5 per cent, solution of soda, in contact with which it is allowed to stand for at least twenty-four hours. The pro- duct is then ground up until a sort of "milk" or emulsion is obtained, and lastly treated with a solution of aniline, so that when pressed into cake, it contains about 33 per cent, of water, and 1 per cent, of aniline.
Dr Miihlhausen, working on these lines in the laboratory, prepared nitro-starch which contained 10.96 and 11.09 per cent, of nitrogen. When in the state of powder it is snow- white in colour ; it becomes electrified when rubbed ; it is
NITRO-STARCH. 105
very stable, and soluble even in the cold in nitroglycerine. He has also prepared a tetra-nitro-starch containing 10.58 and 10.50 per cent, of nitrogen, by pouring water into a solution of starch in nitric acid which had stood for several days. The substance thus produced in the laboratory had all the properties of that prepared by the other process.
The production of penta-nitro-starch is effected by adding 20 grms. of rice-starch — previously dried at a tem- perature of ioo° C, in order to eliminate all moisture — to a mixture of 100 grms. of nitric acid, specific gravity 1.501, and 300 grms. of sulphuric acid, specific gravity 1.8 (some tetra-nitro-starch is also formed at the same time). After standing in contact with these mixed acids for one hour the starch has undergone a change, and the mass ma}- now be discharged into a large quantity of water, and then washed, first with water, and finally with an aqueous solu- tion of soda. The yield in Dr Muhlhausen's experiments was 147.5 Per cent.
The substance thus formed is now heated with ether- alcohol, the ether is distilled off, and the penta-nitro-starch appears as a precipitate, whilst the tetra-nitro-starch, which is formed simultaneously, remains in solution in the alcohol. As obtained by this process, it contained 12.76 and 12.98 per cent, nitrogen, whilst the soluble tetra-nitro-starch contained 10.45 Per cent.
Hexa-nitro-starch is the product chiefly formed when 40 grms. of dry starch are treated with 400 grms. of nitric acid, specific gravity 1.501, and allowed to stand in contact for twenty-four hours ; 200 grms. of this mixture are then poured into 600 c.c. of sulphuric acid of 66° B. The result of this manipulation is a white precipitate, which contains 13.52-13.23 and 1322 per cent, nitrogen; and consists, therefore, of a mixture of penta- and hexa-nitro-starch.
The experiments undertaken with these substances demonstrated that those prepared by precipitating the nitro-starch with strong sulphuric acid were less stable in character or properties than those which were precipitated
io6
NITRO-EXPLOSIVES.
by water or weak sulphuric acid. Dr Miihlhausen is of opinion that possibly in the former case a sulpho-group may be formed, which in small quantity may occasion this instability.
The following table shows the behaviour of these substances prepared in different ways and under various conditions : —
|
Samples. |
|||||
|
^*" " ' A. |
B. |
C. |
D. |
E. |
|
|
Ignition-point - Stability - |
175° C. Stable |
1700 C. Stable |
152° c. Unstable |
121° C. Unstable |
i55QC. Unstable |
|
Per cent, of N. - 96 per cent, al- cohol |
1 1.02 Sol. |
10.54 Sol. |
12.87 Insol. |
12.59 Insol. |
13-52 Insol. |
|
Ether |
Insol. |
Insol. |
Insol. |
Insol. |
Insol. |
|
Ether-alcohol |
Sol. |
Sol. |
Sol. |
Sol. |
Sol. |
|
Acetic Ether |
Sol. |
Sol. |
Sol. |
Sol. |
Sol. |
These samples were prepared as follows : —
A. From 1 part nitric acid and 2 parts sulphuric acid (containing 70 per cent. H20).
B. From 1 part nitric acid and water.
C. From 1 part nitric and 3 parts H.7S04 (con.).
D. From 1 part nitric and 3.5 parts con. H2S04.
E. From 1 part nitric and 3 parts con. H2S04.
Dr Miihlhausen is of opinion that these compounds may be turned to practical account in the production of good smokeless powder. He recommends the following proportions and method. Six grms. of nitro-jute and 2 grms. of nitro-starch are mixed together, and moistened with acetic