134 AN"NUAL KEPORT SMITHSONIAN INSTITUTION, 1917. 



Noble and Abel's formula supposes implicity that the composition 

 of the gaseous products, and as a consequence the covolume of the 

 entire mass, remain invariable whatever the pressure is. As a fact 

 it is not so in most cases because of the operation of the principle of 

 the displacement of the equilibrium. In virtue of this principle the 

 increase of the pressure of the mass of gas causes, when the change 

 is possible, the formation of more and more condensed compounds 

 and, in consequence, the diminution of the covolume. 



It follows that the limit value of 1/A can be such that it will always 

 remain less than a. Hence the pressure can not become infinite. This 

 is the case for guncotton. 



The increase in the proportion of the condensed products is, on the 

 other hand, generally explained by the correlative augmentation of 

 the quantity of heat disengaged, <7o, and of the temperature, 7", of 

 the explosion. The force will then increase with the density of the 

 charge. This is that which takes place in the case of picric acid. 



From the standpoint of variations in the phenomena of detonat^ion 

 it may be said generally that the ability of an explosive to effect the 

 rupture of its envelope is above all determined by an elevated value 

 for its force and for its rate of detonation. Its destructive effect is 

 chiefly a function of the magnitude of its heat, ^, or contra, of its 

 potential. 



2. EFFECTS OF THE DETONATION OF EXPLOSIVES. 



This summary of the theoretical views being disposed of we take 

 up the description of the effects of detonation. We will suppose at 

 the outset that the explosive is subjected to detonation in free air or 

 when contained in a feebly resistant envelope. On explosion the 

 gaseous mass which is produced expands in the direction of least 

 resistance; that is to say, from below upward. This projection of the 

 gas is accompanied with a violent aspiration of the layers of air in 

 the vicinity of the ground, which aspiration is indicated by a brusque 

 depression of the barometer whose intensity diminishes rapidly as 

 the distance from the explosion center increases. Under the influence 

 of this depression the air confined in near-by inclosures tends to es- 

 cape outward and projects in that direction weakly resistant sides 

 such as doors, windows, roofs and the like. The effect appears much 

 as if a charge had been exploded within the inclosure. 



Under the action of this movement of masses of air animated with 

 a high horizontal velocity the layers near the periphery of the gase- 

 ous mass produced by the explosion, and which are animated with a 

 vertical movement, acquire at times a most complete vortex motion. 

 At the same time that this gaseous flow, which is often in a vertical 

 direction, is set up, the detonation engenders a shock wave whose ve- 



