EFFECTS OF EXPLODED NITROGLYCERIN. 427 



are fresh proofs of the enormous initial pressures developed by 

 nitroglycerin. The question of the rapidity of decomposition, 

 moreover, intervenes here (p. 35). 



Although nitroglycerin is shattering, it nevertheless fractures 

 rocks without crushing them into small fragments. The facts 

 observed during the study of the pressures exerted by the 

 crushers, at various densities of charge, would lead us to foresee 

 this property. It may also be accounted for by the phenomena 

 of dissociation. The elements of water and carbonic acid will 

 be partly separated in the first instance, which diminishes the 

 initial pressures ; but the formations of water and carbonic acid 

 being completed during expansion, successively reproduce fresh 

 quantities of heat, which regulate the fall of the pressures. 

 Nitroglycerin will therefore act during expansion in a similar 

 manner to ordinary powder. However, the dissociation will 

 be less with nitroglycerin, because the compounds formed are 

 simpler and the initial pressures higher. 



In short, nitroglycerin combines the apparently contradictory 

 properties of various explosive substances : it is shattering, like 

 nitrogen chloride ; dislocates and fractures rocks without crush- 

 ing them, like ordinary powder, though with more intensity ; 

 lastly, it produces excessively great effects of projection. All 

 these properties, recognised by observers, can be foreseen and 

 explained by theory. 



16. It could further be shown that inflammation induced at 

 a point of the mass is less dangerous with nitroglycerin than 

 with chlorate and even nitrate powder, seeing that the com- 

 bustion of the same weight of matter raises the temperature of 

 the neighbouring parts to a less extent, either owing to the 

 cooling produced by contact with the surrounding liquid parts, 

 or, especially, owing to the specific heat of nitroglycerin, which 

 appears to be much greater than that of potassium chlorate and 

 nitrate powders. 



With regard to the theory of the effects of shock on nitro- 

 glycerin, the reader is referred to p. 52. 



17. Lastly, let us compare nitroglycerin with ordinary powder 

 from the point of view of the best use of a given weight of 

 potassium nitrate. According to the equivalent, 303 parts of 

 nitre produce either 404 parts of ordinary powder, or 227 parts 

 of nitroglycerin, that is to say, a weight less by half. But as 

 a set-off the latter can develop, under the most favourable 

 circumstances, a pressure from eight to ten times greater than 

 the same volume of powder. 



It follows from these numbers that a given weight of 

 potassium nitrate, if it could be changed atomically, and with- 

 out loss, into nitroglycerin, would develop in a blast-hole a 

 pressure treble that yielded by ordinary powder, made with the 

 same weight of nitrate. 



