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NITRO-EXPLOSIVES
[Illustration: DANGER BUILDING SHOWING PROTECTING MOUNDS. (_See page 6._)]
NITRO-EXPLOSIVES
A PRACTICAL TREATISE
CONCERNING THE
_PROPERTIES, MANUFACTURE, AND ANALYSIS OF NITRATED SUBSTANCES, INCLUDING
THE FULMINATES, SMOKELESS POWDERS, AND CELLULOID_
BY
P. GERALD SANFORD, F.I.C., F.C.S.
_Public Analyst to the Borough of Penzance; late Consulting Chemist to the
Cotton Powder 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_
~Second Edition, Revised and Enlarged~
PREFACE.
In 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 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 1896._
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 Company
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 composition, as these
details have not, in several cases, been made public.
P. GERALD SANFORD.
LONDON, _June 1906._
TABLE OF CONTENTS.
CHAPTER I.--INTRODUCTION.
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.
CHAPTER II.--NITRO-GLYCERINE.
Properties of Nitro-Glycerine--Manufacture--Nitration--Separation--Washing
and Filtering--Drying, Storing, &c.--The Waste Acids--Their Treatment--
Nitric Acid Plants
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 SteepingWhirling 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
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--Composition of Gelignite--Blasting Gelatine--Gelatine
Dynamite--Absorbing Materials--Wood Pulp--Potassium Nitrate, &c.--
Manufacture, &c.--Apparatus Used--The Properties of the Gelatine Compounds
CHAPTER V.--NITRO-BENZOL, ROBURITE, BELLITE, PICRIC ACID, &c.
Explosives derived from Benzene--Toluene and Nitro-Benzene--Di- and
Tri-nitro-Benzene--Roburite: Properties and Manufacture--Bellite:
Properties, &c.--Securite--Tonite No. 3.--Nitro-Toluene--
Nitro-Naphthalene--Ammonite--Sprengel's Explosives--Picric Acid--
Picrates--Picric Powders--Melinite--Abel's Mixture--Brugère's Powders--
The Fulminates--Composition, Formula, Preparation, Danger of, &c.--
Detonators: Sizes, Composition, Manufacture--Fuses, &c.
THE FULMINATES.
Composition, Formula, Preparation, Danger of, &c.--Detonators: Sizes,
Composition, Manufacture--Fuses, &c.
CHAPTER VI.--SMOKELESS POWDERS IN GENERAL.
Cordite--Axite--Ballistite--U.S. Naval Powder--Schultze'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.
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
of Nitrogen--Lungé, 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
Fulminate--Cap Composition--Table for Correction of Volumes of Gases, for
Temperature and Pressure
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.
CHAPTER IX.--THE DETERMINATION OF THE RELATIVE STRENGTH OF EXPLOSIVES.
Effectiveness of an Explosive--High and Low Explosives--Theoretical
Efficiency--M.M. Roux and Sarrau's Results--Abel and Noble's--Nobel's
Ballistic Test--The Mortar--Pressure or Crusher Gauge--Calculation Volume
of Gas Evolved, &c.--Lead Cylinders--The Foot-Pounds Machine--Noble's
Pressure Gauge--Lieut. Walke's Results--Calculation of Pressure Developed
by Dynamite and Gun-Cotton--McNab'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, &c.
INDEX
LIST OF ILLUSTRATIONS.
FRONTISPIECE--Danger Building showing Protecting Mounds.
1. Section of Nitro-Glycerine Conduit
2. Melsens System of Lightning Conductors
3. French System
4_a_ & 4_b_. English Government System
5. Upper Portion of Nitrator for Nitro-Glycerine
6. Small Nitrator
7. Nathan's Nitrator
8. Nitro-Glycerine Separator
9. Nitro-Glycerine Filtering Apparatus
10. Cotton-Waste Drier
11. Dipping Tank
12. Cooling Pits
13. Steeping Pot for Gun-Cotton
14. Hydro-Extractor or Centrifugal Drier
15_a_ & 15_b_. Gun-Cotton Beater
16_a_. Poacher for Pulping Gun-Cotton
16_b_. Plan of same
16_c_. Another form of Poacher
17 & 18. Compressed Gun-Cotton
19. Hydraulic Press
20. Thomson's Apparatus--Elevation
21. Elevation Plan
22. Trench's Safety Cartridge
23. Vessel used in Nitrating Paper
24. Cage ditto--White & Schupphaus' Apparatus
25. Do. do. do.
26 & 27. Nitrating Pot for Celluloid
28 & 29. Plunge Tank in Plan and Section
30. Messrs Werner, Pfleiderer & Perkins' Mixing Machine
31. M. 'Roberts' Mixing Machine for Blasting Gelatine
32. Plan of same
33. Cartridge Machine for Gelatines
34. Cartridge fitted with Fuse and Detonator
35. Gun-Cotton Primer
36. Electric Firing Apparatus
37. Metal Drum for Winding Cordite
38. Ten-Stranding
39. Curve showing relation between Pressures of Cordite and Black Powder,
by Professor Vivian Lewes
40. Marshall's Apparatus for Moisture in Cordite
41. Lungé's Nitrometer
42. Modified do.
43. Horn's Nitrometer
44. Schultze-Tieman Apparatus for Determination of Nitrogen in Gun-Cotton
45. Decomposition Flask for Schultze-Tieman Method
46. Abel's Heat Test Apparatus
47. Apparatus for Separation of Nitro-Glycerine from Dynamite
48. Test Tube arranged for Heat Test
49. Page's Regulator
50. Do. showing Bye-Pass and Cut-off Arrangement
51. Will's Apparatus
52 & 53. Curves obtained
54. Dynamite Mortar
55. Quinan's Pressure Gauge
56. Steel Punch and Lead Cylinder for Use with Pressure Gauge
57. Micrometer Calipers for Measuring Thickness of Lead Cylinders
58. Section of Lead Cylinders before and after Explosion
59. Noble's Pressure Gauge
60. Crusher Gauge
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 propulsive 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.[A]
[Footnote A: Definition given in Order of Council, No. 1, Explosives Act,
1875.]
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., 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 importance 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 NO_{2} group, known as nitryl, has been substituted in place of
hydrogen.
Thus in glycerine,
|OH
C_{3}H_{5}|OH,
|OH
which is a tri-hydric 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 explosive compound,
nitro-glycerine. If one atom only is thus displaced, the mono-nitrate is
formed thus,
|ONO_{2}
C_{3}H_{5}|OH;
|OH
and if the three atoms are displaced, C_{3}H_{5}(ONO_{2})_{3}, or the tri-
nitrate, is formed, which is commercial nitro-glycerine.
Another class, the nitro-celluloses, are formed from cellulose,
C_{6}H_{10}O_{5}, 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. The hexa-nitrate, or
gun-cotton, has the formula, C_{12}H_{14}O_{4}(ONO_{2})_{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 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, C_{6}H_{6}, prepared from the light oil obtained from coal-tar,
when nitrated forms nitro-benzenes, such as mono-nitro-benzene,
C_{6}H_{5}NO_{2}, and di-nitro-benzene, C_{6}H_{4}(NO_{2})_{2}, in which
one and two atoms are replaced by the NO_{2} group. The latter of these
compounds is used as an explosive, and enters into the composition 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,
C_{6}H_{4}X_{2}, give, however, three series. They are called ortho, meta,
or para compounds, depending upon the position of NO_{2} 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 compound 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, C_{6}H_{5}.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.[A]
[Footnote A: "Organic Chemistry," Prof. Hjelt. Translated by J.B. Tingle,
Ph.D.]
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, C_{6}H_{5}.OH, is nitrated, a
compound is formed known as tri-nitro-phenol, or picric acid,
C_{6}H_{2}(NO_{2})_{3}OH, which is used very extensively as an explosive,
both as picric acid and in the form of picrates. Another nitro body that
is used as an explosive is nitro-naphthalene, C_{10}H_{6}(NO_{2})_{2}, in
roburite, securite, and other explosives of this class. The hexa-nitro-
mannite, C_{6}H_{8}(ONO_{2})_{6}, is formed
[Illustration: No. 1]
[Illustration: META-DINITRO-BENZENE No.2]
by treating a substance known as mannite, C_{6}H_{8}(OH)_{6}, 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, C_{12}H_{16}O_{6}(ONO_{2})_{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 25° 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 by Mühlhäuer. The former chemists give
jute the formula C_{12}H_{18}O_{9}, and believe that its conversion into a
nitro-compound takes place according to the equation--
C_{12}H_{18}O_{9} + 3HNO_{3} = 3H_{2}O + C_{12}H_{15}O_(6}(NO_{3})_{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 C_{12} formula, it will contain four hydroxyl (OH) groups,
or two less than cellulose similarly represented." It contains 11.5 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 nitro-glycerine 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).[A] 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.
[Footnote A: 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
construction 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).]
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., also the
character, and construction of all the mounds, and nature of the processes
to be carried on in the factory or building.[A]
[Footnote A: Explosives Act, 38 Vict. ch. 17.]
[Illustration: FIG. 1.--SECTION OF NITRO-GLYCERINE CONDUIT. _a_, lid; _b_,
lead lining; _c_, cinders.]
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 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. 1), 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 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 conduits are of course
those concerned with the manufacture of nitro-glycerine. These buildings
are--(1) 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 lightning 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 thermometer should be
suspended in every house. It is very 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[A]--
C_{3}H_{5}(NO_{3})_{3} + 3KOH = C_{3}H_{8}O_{3} + 3KNO_{3}.
[Footnote A: See also Berthelot, _Comptes Rendus_, 1900, 131[12], 519-
521.]
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 importance 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 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.
[Illustration: FIG. 2.--MELSENS SYSTEM OF LIGHTNING CONDUCTORS.]
~Lightning Conductors.~--The Explosive Substances Act, 38 Vict. ch. 17,
clause 10, says, "Every factory magazine and expense magazine in a
factory, and every danger building 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
conductor."
The exact form of lightning conductor most suitable for explosive works
and buildings has not yet been definitely 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.
Professor Melsens[A] 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 _Arms and Explosives_.
[Footnote A: Belgian Academy of Science.]
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.
[Illustration: Fig. 3.--FRENCH SYSTEM OF LIGHTNING CONDUCTORS.]
The French system of protecting powder-magazines is shown in Fig. 3, where
there are no brush terminals or aigrettes. The French military authorities
also protect magazines by erecting two or more lightning-rods on poles of
sufficient height placed close to, but not touching, the walls of the
magazine. 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 fork
or aigrette of five or more points should invariably be used in place of a
single point.
[Illustration: FIG. 4_a_.--GOVERNMENT SYSTEM OF LIGHTNING CONDUCTORS FOR
LARGE BUILDINGS.]
[Illustration: FIG. 4_b_.--GOVERNMENT SYSTEM OF LIGHTNING CONDUCTORS FOR
SMALL BUILDINGS.]
In Fig. 4 (_a_ and _b_) is shown the Government method for protecting
buildings in which explosives are made or 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 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 buildings, be spaced at intervals of 50 feet. There will then be
no point on the building more than 25 feet from the conductor. This
"25-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 buildings, 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 connected 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 periodically 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 may 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 is also very handy,
consisting of a case containing three Leclanché 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
dynamite 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 saltpetre, 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 dynamite, that the use of nitro-glycerine as an explosive became
general.
Among those who improved the manufacture of nitro-glycerine was Mowbray,
who, by using pure glycerine and nitric acid free from nitrous acid, made
very great advances in the manufacture. Mowbray was probably 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,[A] proposed
to prepare nitro-glycerine by mixing 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 proportions--Glycerine, 100; nitric acid, 280; and
sulphuric acid, 600. They state that the rise of temperature upon mixing
is limited from 10° 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 nitration 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.
[Footnote A: _Comptes Rendus_, 75; and Desortiaux, "Traité sur la Poudre,"
684-686.]
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 which would be lost in the subsequent
process of washing to which the nitro-compound 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 compound of glycerol, was thought to be formed thus--
C_{3}H_{8}O_{3} + 3HNO_{3} = C{3}H_{5}(NO_{2})_{3}O_{3} + 3H_{2}O;
but more recent researches rather point to its being regarded as a nitric
ether of glycerol, or glycerine, and to its being formed thus--
C_{3}H_{8}O_{3} + 3 HNO_{3} = C{3}H_{5}(NO_{3})_{3} + 3H_{2}O.
92 227
|OH
The formula of glycerine is C_{3}H_{8}O_{8}, or C_{3}H_{5}|OH
|OH
|ONO_{2}
and that of the mono-nitrate of glycerine, C_{3}H_{5}|OH
|OH
|ONO_{2}
and of the tri-nitrate or (nitro-glycerine), C_{3}H_{5}|ONO_{2}
|ONO_{2}
that is, the three hydrogens of the semi-molecules of hydroxyl in the
glycerine have been replaced by the NO_{2} 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
2.47 lbs. of nitro-glycerol ((227+1)/92 = 2.47), 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.