374 GENERAL DATA. 



(2) The smallest shock which will cause decomposition, also 

 the effects due to the shock, or the application of fire would be, 

 no doubt, derived therefrom in a complete theory. 



In the absence of this theoretical datum, we measure the 

 minimum fall of a given weight which is required to cause the 

 substance to explode when placed in definite conditions. 



More generally, but in a vaguer manner, we ascertain whether 

 it explodes by the shock of iron on iron, bronze on bronze, 

 stone on stone, wood on wood, iron on bronze, stone, wood, 

 bronze on stone or wood, stone on wood, or by friction exercised 

 in various conditions, etc. 



9. The law of the rapidity of decomposition, in cases of 

 simple ignition, and the rapidity of propagation of the explosive 

 wave in other cases (p. 88), is of primary importance, but this 

 law is generally not known. 



10. The total work performed by an explosive substance 

 in given conditions corresponds to the difference between the 

 heat liberated by the chemical transformation effected without 

 external work and the heat really liberated in the conditions of 

 the experiment, a difference which might, if necessary, be 

 measured experimentally. 



In principle the maximum work would be measured by the 

 liberated heat itself (potential energy), but we have only to con- 

 sider the work which may be performed by the gases developed 

 by the explosion in the case of indefinite expansion. The theory 

 of these effects has only been broached for service powder 

 (p. 17). 



11. In practice this deficiency is made up by empirical 

 notions drawn from the study of the effects of each explosive on 

 various kinds of vessels and materials. These effects are more- 

 over complex, for they often result at the same time from the 

 total work, the pressure exercised, the law of rapidity, and the 

 nature of the materials. 



Without entering into circumstantial details, may be cited 

 as an instance the trial of the force of an explosive substance 

 according to the size of the capacity produced by its explosion 

 in a block of lead (Abel's process). For instance, a block of 

 lead is taken, 250 mm. square, 280 mm. high, and weighing 

 175 kgnL Following the axis, a cylindrical channel is bored 

 with a diameter comparable to that of a miner's boring tool 

 (28*5 mm.), and 178 mm. deep. A determinate weight of the 

 explosive substance (10, 20, or 30 grms.) is placed at the bottom, 

 and if necessary it can be arranged under an impermeable 

 covering. A detonator is introduced at the end of a fuse of 

 suitable length, and the hole is then filled up with water, which 

 serves as tamping. The explosion is then effected, and the 

 capacity of the pear-shaped chamber produced is afterwards 

 measured. The proportion between the increase of the capacities 



