378 GENERAL DATA. 



Thus too sudden a reaction brought about in a firearm causes 

 its rupture before the projectile has time to be displaced. Any 

 substance capable of producing such effects must be excluded, 

 and this prevents the employment of pure nitroglycerin or 

 potassium picrate in firearms. 



A shell should be broken into large pieces and not pulverised 

 by the explosion of the internal substance, and this circumstance 

 opposes the use of pure mercury fulminate. The reaction of 

 the powder in the weapon should be sufficiently progressive for 

 the projectile to acquire a determinate initial velocity. 



8. From a more particular point of view, the explosive sub- 

 stance should not injure the weapons ; either by chemical 

 reaction, sulphurising, oxidation, etc,, or by fouling (ash and 

 fixed substances, leading, etc.), or by mechanical wear and tear. 



9. In subterranean works the explosive substance must not 

 produce any deleterious gases capable of suffocating the workmen 

 (carbonic oxide, sulphuretted hydrogen, nitrous vapours, 

 hydrocyanic vapours, etc,). 



In general it should not produce too much smoke in warfare. 



10. On the contrary, in certain military operations it may be 

 useful to produce a great deal of smoke, in order, for instance, to 

 mask a movement or some works. 



It may also be useful to produce deleterious gases in order to 

 render the gallery of a mine, etc., impracticable for some time. 



11. The pyrotechnical effects, such as signals, lighting, bon- 

 fires, etc., represent quite a different order of special conditions 

 to be fulfilled, but on which we shall not dwell, as this subject 

 is foreign to the present work. 



12. The necessity of dividing the explosive substances, or of 

 making them into a determinate form, enters into consideration 

 sometimes. 



Thus dynamite and the powders properly so called are more 

 easily divided than gun-cotton into small pulverulent masses, 

 destined to be introduced into some cavity whose cracks and 

 fissures they fill up, such as a blast^hole. 



On the other hand, compressed gun-cotton may be easily 

 divided and worked with tools so as to give it a special form 

 independent of any covering ; special care is taken to impregnate 

 it beforehand with paraffin, a substance which moreover has the 

 advantage of diminishing the explosive sensitiveness of gun- 

 cotton. 



13. In various cases the explosive substances are compressed 

 or agglomerated under an hydraulic press in order to increase the 

 density and modify the law of propagation of the ignition. Black 

 powder and gun-cotton are very suitable for this operation, which 

 it would be perilous to attempt with fulminate or chlorate powders. 



14. Let us cite again the employment of fulminating sub- 

 stances under the form of caps, ordinary or strong detonators, 



