434 DYNAMITES. 



base, and that this mixture should remain uniform without 

 chemical change and without exudations due to shocks in 

 transport or to variations in temperature, otherwise we should 

 be brought back to the drawbacks and dangers of pure nitro- 

 glycerin. The absorbent substance must, therefore, have a 

 special structure opposing itself to the spontaneous separation 

 of the nitroglycerin. Dynamites having as base ordinary sand, 

 brick-dust, and powdered coke have thus been set aside owing 

 to their instability. 



The presence of an excess of nitroglycerin beyond the satura- 

 tion point may even diminish the strength of a dynamite instead 

 of increasing it, owing to the difference of the mode of propaga- 

 tion of the explosive wave in the liquid and in the porous 

 mixture. It is in this way that the crushing effects upon a 

 leaden block are more marked with 75 per cent, dynamite than 

 with a richer dynamite, and even with pure nitroglycerin. 



13. This tendency to separation is increased by a special 

 property of nitroglycerin, which plays an important part in the 

 application of all dynamites formed by this agent, viz. the 

 solidification of nitroglycerin at about 12. In fact, in becoming 

 solidified, the explosive more or less completely separates itself 

 from its absorbent, and thenceforth constitutes a new system, 

 endowed with special properties. 



On the one hand, solid nitroglycerin seems less sensitive to 

 shocks, and especially to their transmission step by step. It 

 requires more powerful fuses to explode it, which generally 

 renders it necessary to reheat the cartridges in order to liquefy 

 it, and to reconstitute the original dynamite, an operation which 

 has occasioned numberless accidents in mines. 



On the other hand, nitroglycerin thus liquefied, after having 

 been partly separated from its absorbent by crystallisation, may 

 not mix with it again in so intimate a manner as before, 

 especially if the absorbent be not of good quality, and if it be 

 submitted to pressure. 



14. The degree of sensitiveness to shock of dynamites is 

 a circumstance of fundamental importance, particularly for 

 military applications. Thus it is necessary to put into the 

 hands of soldiers a substance which does not explode during 

 transport, nor under the shock of a ball. Ordinary dynamite 

 with silica base does not satisfy this condition, which has often 

 caused compressed gun-cotton to be preferred, though the latter 

 is not entirely free from danger in this respect. 



15. It has been attempted to gain the end in view by adding 

 certain foreign substances to dynamites camphor, for instance, 

 to the amount of a few hundredth parts ; but this mixture is 

 only moderately efficacious. 



The condition sought after is especially realised by blasting 

 gelatin, formed of nitroglycerin and collodion cotton. But here 



