RELATION OP OXYGEN TO COMBUSTIBLE. 3 



composition of an explosive substance. Take, for instance, 

 diazobenzol and nitrogen sulphide or chloride, bodies which are 

 formed with absorption of heat from their elements, and which 

 decompose with a reverse thermal action. * 



An explosive compound may be employed either in a pure 

 state or mixed with an inert substance, as in the case of 

 dynamite, a mixture of silicious earth and nitroglycerin. 



The effect of such mixture is to diminish the violence of the 

 explosion, and to give to it a propelling or rending action rather 

 than a shattering one. 



Or an explosive compound may be mixed with a substance 

 which increases the force of the explosion, as in the case of 

 nitroglycerin mixed with an active base. And here it is well 

 to distinguish three fundamental cases, based on the relation 

 between the oxygen and the combustible elements in the ex- 

 plosive body. 



This relation is either that of a total combustion, as in the 

 case of silver oxalate, resolvable by the explosion into carbonic 

 acid and metallic silver. 



C 2 Ag 2 4 = 2C0 2 + Ag 2 . 



Or the oxygen is deficient, which is the case in potassium 

 picrate and in gun-cotton. 



Or, on the contrary, the oxygen is in excess; which is the 

 case in nitromannite and nitroglycerin. 



In the last case there may be an advantage in utilising the 

 whole energy of the explosive body by adding a combustible 

 such as carbon, or better, nitrocotton, an explosive in itself, in 

 suitable proportions. 



In the second case, where there is a deficiency of oxygen, an 

 oxidising agent such as potassium nitrate, may be added to the 

 explosive. 



Mixtures, however, in which total combustion takes place are 

 not always those which produce the greatest effect in a given 

 weight and under given conditions. 



Gunpowder, for example, mixed with a quantity of nitre 

 sufficient for complete combustion, develops, weight for weight, 

 less gas, and consequently less pressure, and produces less effect 

 than ordinary powder, in which there is a deficiency of oxygen. 



The effects which result from the substitution of one salt for 

 an equivalent salt, in explosive mixtures, deserve particular 

 attention. Let us confine ourselves to the nitrates and to 

 a simple substitution which does not change the nature of the 

 powder; for instance, sodium nitrate, or barium nitrate, for 

 potassium nitrate. 



The substituted salt, in equivalent proportions, would hardly 

 change the amount of heat liberated nor the volume of the 

 gases in the case of total combustion. 



