cerin have resulted from carelessness in thawing the explosive.

How to Thaw Nitroglycerin when Frozen.-When frozen, nitroglycerin may be conveniently and safely thawed by placing the vessel containing it in another vessel containing water not hotter than the hand can bear (about 100° F.) and allowing it to remain, replenishing the warm water when necessary, until the explosive is thawed. Under no circumstances should frozen nitroglycerin be put in the same vessel as the water, nor should it be placed near an open fire nor in contact with any heated surface, nor, in short, thawed in any other way than as just directed.

Decomposition of Nitroglycerin.-Pure nitroglycerin does not spontaneously decompose at any ordinary temperature, but, as in the case of guncotton, the presence of free acid combined with heat quickly leads to its decomposition. High temperature alone does not injure thoroughly purified nitroglycerin, and the presence of any acid is determined by shaking a few drops in water and testing the water with blue litmus paper. While undergoing decomposition nitroglycerin becomes exceedingly dangerous, the slightest shock causing violent explosion; but unless a very large quantity is involved serious accidents can be prevented by exercising ordinary care. Decomposition of nitroglycerin is detected by the acid reaction on litmus paper and expecially by the explosive becoming greenish in appearance. When in this condition nitroglycerin should be very carefully removed and exploded.

Recapitulation.-1. Guncotton is an explosive compound made by immersing pure dry cotton in a mixture of the purest and strongest nitric and sulphuric acids.

2. The best proportions of the acids in the mixture are 1 part of nitric acid to 3 parts of sulphuric acid, while those of the cotton and the mixture are 1 part of the former to 10 parts of the latter.

3. The several steps in the manufacture of guncotton have for their objects:

(1) The thorough drying and cleansing of the materials.

(2) The complete conversion of the cotton into gun

cotton.

(3) The removal of every trace of free acid from the

guncotton.

4. Guncotton is one of the safest explosives known, being absolutely inexplosive when it contains 30 per cent. of water, and is an excellent service explosive.

5. Nitroglycerin is an explosive compound obtained from the action of a mixture of the purest and strongest nitric and sulphuric acids upon pure anhydrous glycerin.

6. The proportions of acids in the mixture are 1 part of nitric acid to 2 parts of sulphuric acid, while those of the glycerin and the mixture are about 1 part of the former to 4 or 5 parts of the latter.

7. Thoroughly purified nitroglycerin is comparatively safe (unless frozen), and not liable to undergo decomposition.

8. When frozen, nitroglycerin becomes dangerously sensitive, and it should be thawed only in the manner prescribed.

9. Both guncotton and nitroglycerin are liable to decompose when they contain free acid and are exposed to high temperatures.

10. When found to be decomposing these explosives should be carefully removed and immediately exploded.

CHAPTER VI

GUNCOTTON POWDERS. DYNAMITE.

DETONATORS

Guncotton and nitroglycerin are the most powerful known explosives and, on account of their tremendous explosive force, are unsuitable for many military and industrial purposes. In order to modify and regulate their action they are mixed with other substances, the resulting mixtures being known as guncotton powders and dynamite.

Dynamite. At present dynamite is a generic term and includes all explosives made by absorbing liquid nitroglycerin in solid materials which are capable of retaining it.

The solid material used to absorb nitroglycerin (or the absorbent) is technically called the "dope."

The absorbent may be entirely inert and used to convert nitroglycerin from the liquid into the solid form, or, on the other hand, it may itself be an explosive. In the first case the explosive force, bulk for bulk, of the resulting explosive will be diminished, whereas in the second case it will be increased.

1

Kieselguhr Dynamite or Giant Powder.-This is one of the earliest and best-known forms of dynamite, and consists essentially of a mixture of kieselguhr1 and nitroglycerin, to which is added a very small percentage of sodium (or other alkaline) carbonate to neutralize any traces of free acid that may remain in the nitroglycerin.

'Kieselguhr is one of the best-known "dopes," being perfectly inert and possessing very high absorptive power, the best varieties being able to absorb and retain 82 per cent. of nitroglycerin. It is largely organic in its composition, containing decomposed shells of myriads of diatoms, which preserve their cellular formation even after calcination.

The kieselguhr is first calcined, pulverized, and thoroughly dried. It is then weighed and put into the mixing troughs.

The nitroglycerin is brought to the mixing house in guttapercha or lacquered wood-pulp buckets and poured directly upon the absorbent, or it may be brought to the troughs through stout rubber hose.

The proportions vary with the grade of dynamite required. The mixing is done entirely by hand, the workmen wearing usually india-rubber gloves during the operation. After the nitroglycerin has been entirely absorbed, the dynamite is rubbed through wire sieves so as to distribute the nitroglycerin uniformly throughout the mass.

Properties of Dynamite.-Kieselguhr dynamite is a granular substance, the color of which varies from pearl-gray to reddish-brown; it is of the plastic consistency of moist clay. It should not feel greasy to the touch, nor should there be any trace of free nitroglycerin on the sides of the containing box or cartridge wrapper. Dynamite possesses the physical properties of nitroglycerin and is therefore equally poisonous. Its firing-point is about 356° F., and at this temperature it either burns or explodes; if free from pressure, confinement, jar, or vibration, it burns; otherwise it explodes. High temperatures below its firing-point cause dynamite "to leak," that is, the nitroglycerin exudes from the base (or dope). When this occurs the danger attending liquid nitroglycerin is ever present. Dynamite freezes at about 40° F., and, once frozen, it remains in this condition at temperatures considerably above its freezing-point. Although less sensitive when frozen, the fact that it is still a "high explosive" must always be remembered. When frozen it can be detonated only with difficulty and always with greatly diminished force. It is therefore recommended to thaw frozen dynamite before using it.

All nitroglycerin preparations, when heated gradually up to their exploding points, become dangerously sensitive to the

slightest shock or blow, and, once that point is reached, they no longer ignite but explode violently; and further, on account of the poor conductivity of the material, a very small portion of dynamite in contact with the source of heat may reach this point and cause the explosion of the rest of the mass, which may be considerably below the danger point.

How to Thaw Dynamite When Frozen.-The best way to thaw frozen dynamite is to open the packages carefully and place them in a room where the temperature does not exceed 150° F., and allow the explosive to thaw gradually. A room heated by steam is to be preferred.

If there is not time to follow this method, the best way is to place the cartridges in a water-tight can, and suspend this can in another vessel containing water not hotter than the hand can bear.

Under no circumstances should an attempt be made to thaw any form of dynamite by placing it near a hot fire, nor directly on a hot shovel or plate; nor by leaning it against hot brickwork, steam boilers, or radiators; in short, never attempt to thaw dynamite in any other way than as indicated above.

Explosive Gelatin.-This explosive is made by dissolving the soluble variety of guncotton in nitroglycerin. For military purposes the proportions of the ingredients are about 4 parts of guncotton to 92 parts of nitroglycerin, to which are added 4 parts of camphor. The camphor is added to increase the elasticity and solidity of the explosive, while at the same time it reduces its sensitiveness. As might be expected from combining the two strongest known explosives, the resulting compound is the most powerful form of dynamite.

Properties of Explosive Gelatin.-Explosive gelatin has the appearance of a jelly-like paste, which has a honeyyellow color, and a consistency varying from tough leather to ordinary jelly. It does not absorb water, and when placed in it only a very small quantity of nitroglycerin is dissolved