Dynamite.
—As combustion takes place more rapidly in nitro-glycerine than in gun-cotton, the effects of dynamite are more shattering than those of the latter substance. Gun-cotton holds, indeed, a mean position in this respect between dynamite, on the one hand, and gunpowder on the other. Dynamite is, therefore, even less suitable than gun-cotton for those uses which are required to give the produce in large blocks. But in very hard and tough rock, it is considerably more effective than gun-cotton, and, under some conditions, it will bring out rock which gun-cotton fails to loosen.
Dynamite is unaffected by water, so that it may be used in wet holes; indeed, water is commonly used as tamping, with this explosive. In upward holes, where water cannot, of course, be used, dynamite is generally fired without tamping, its quick action rendering tamping unnecessary.
The pasty form of dynamite constitutes a great practical advantage, inasmuch as it allows the explosive to be rammed tightly into the bore-hole so as to fill up all empty spaces and crevices. This is important, for it is obvious that the more compactly the charge is placed in the hole, the greater will be the effect of the explosion. Moreover, this plastic character renders it very safe to handle, as blows can hardly produce sufficient heat in it to cause explosion. If a small quantity of dynamite be placed upon an anvil and struck with a hammer, it explodes readily; but a larger quantity so struck does not explode, because the blow is cushioned by the kieselguhr. If ignited in small quantities in an unconfined space, it burns quietly without explosion.
If dynamite be much handled out of the cartridges, it causes violent headaches; and the same effect is produced by being in a close room in which there is dynamite in the unfrozen state.
Dynamite possesses one quality which places it at a disadvantage with respect to other explosives, namely, that of freezing at a comparatively high temperature. At about 40° F. the nitro-glycerine solidifies, and the dynamite becomes chalky in appearance. In this state, it is exploded with difficulty, and, consequently, it has to be thawed before being used. This may be safely done with hot water; performed in any other way the operation is dangerous.
The products of the combustion of dynamite are carbonic acid, carbonic oxide, water, and nitrogen. As, however, there is more than a sufficiency of oxygen in the compound, but little of the oxide is formed when the charge is not excessive. If, therefore, dynamite be properly detonated, and overcharging be avoided, its explosion will not greatly vitiate the atmosphere. But if it be only partially detonated hypo-nitric fumes are given off, which have a very deleterious effect upon the health. It is, thus, of the highest importance that complete detonation should be effected, not merely to obtain the full effect of the explosive, but to avoid the formation of this noxious gas. This may be done by using a detonator of sufficient strength, and placing it well into the primer.
Firing Points of the Common Explosive Compounds.
—The following table shows the temperatures at which the commonly used compounds explode:—
| When slowly Heated. | When suddenly Heated. | |
|---|---|---|
| Gunpowder | .. | from 500° to 540° |
| Gun-cotton | 360° | 482° |
| Kieselguhr dynamite | 356° | 446° |
| Cellulose dynamite | 342° | 446° |