38 DURATION OF EXPLOSIVE REACTIONS. 



viz. towards 160 to 180, a point which is near the temperature 

 of the rapid decomposition of the substance. 



3. When two different explosive substances are compared, 

 which are decomposed at the same temperature and with similar 

 rapidity, their relative sensitiveness to shock and friction, at a lower 

 temperature, depends on the quantity of matter over which, from 

 the first instant, the work of the shock or of the friction is dis- 

 tributed; that is to say, it depends on the cohesion of the 

 substance, which regulates at the point struck the transforma- 

 tion of energy into heat, and consequently, the temperature 

 developed around this point. 



4. Cohesion, also, generally intervenes in the case of direct 

 inflammation ; the same quantity of heat produced by the com- 

 bustion of the first portions, being able to raise to the degree of 

 decomposition the temperature of a small quantity of matter, to 

 which it is exclusively applied, while if it be distributed over a 

 greater mass the temperature of the latter will not be raised to 

 the degree requisite for the decomposition to be propagated. 



5. The mass heated remaining the same, and the substances 

 being different, the sensitiveness depends on the initial temperature 

 at which decomposition commences. This temperature being con- 

 siderably lower, for example, for potassium chlorate than for 

 the nitrate, the chlorate powder will be more sensitive in this 

 respect. 



6. The sensitiveness depends furthermore on the quantity of 

 heat liberated by decomposition ; that is to say, that the sensitive- 

 ness will be greater, all things else being equal, if the reaction 

 liberates more heat. 



7. The same quantity of heat will produce different effects on the 

 same weight of matter according to the specific heat of the latter. 

 For instance, potassium chlorate, the specific heat of which is 

 0*209, substituted for an equal weight of potassium nitrate, of 

 which the specific heat is 0*239, in the composition of an 

 explosive mixture should give, and in fact does give, a more 

 sensitive powder than the nitrate. 



This condition contributes, with the lower temperature of 

 decomposition and the absence of cohesion, to render the chlorate 

 powders eminently dangerous. 



4. MOLECULAR KAPIDITY OF THE KEACTIONS. 



First Section. General Phenomena. 



1. The rapidity of a reaction must be regarded in a different 

 manner according as it is the question of a homogeneous system, 

 and especially of a gaseous system, submitted to identical con- 

 ditions of temperature and pressure in all its parts, or if the 

 system be submitted at one point to a rise in temperature or 



