68 DURATION OF EXPLOSIVE REACTIONS. 



are liberated. The electric arc accelerates in a peculiar degree 

 the decomposition of the cyanogen in which it is produced, yet 

 without rendering it explosive. 1 Nitrogen and the oxygen of 

 the nitric oxide also separate on the passage of the electric 

 spark. As a matter of fact the oxygen of this latter gas 

 becomes united with the excess of the surrounding oxide and 

 generates nitric peroxide. A portion of the hydrogen and of 

 the carbon liberated at the expense of the acetylene also 

 reunites under the influence of the electricity so as to recon- 

 stitute this hydrocarbon, the whole forming a system in 

 equilibrium. 2 To these circumstances might be attributed 

 the absence of the propagation of the decomposition, but this 

 explanation is not sufficient for the cyanogen, which becomes 

 entirely decomposed, 3 without possibility of reconversion. 



Nor does this suffice for arseniuretted hydrogen, a gas 

 decomposable, according to Ogier, with liberation of 36,700 cal. 

 (AsH 3 = 78 grms.). 



This latter gas is so very unstable that it is continually 

 decomposing at normal temperature, if kept in sealed glass 

 tubes. It is well known with what facility even the last trace 

 is decomposed by heat in Marsh's apparatus. A series of 

 electric sparks will also completely destroy it. Nevertheless, 

 arseniuretted hydrogen does not explode, as the author has 

 shown, either under the influence of progressive heat or under 

 that of the electric sparks. 



3. Thus, in the endothermal combinations already enumerated, 

 there exists a condition, associated with their molecular con- 

 stitution, which prevents the propagation of the chemical action 

 under the influence of mere progressive heating or of the 

 electric spark, at least so long as the temperature remains below 

 certain limits. 



We are aware that the study of explosive substances presents 

 circumstances which are analogous. The simple ignition of 

 dynamite, for instance, would not suffice to cause its explosion ; 

 on the contrary, Nobel has shown that explosion is produced by 

 the influence of special detonators, such as mercury fulminate, 

 and which are susceptible of developing a very violent shock. 

 The thermodynamic theory has already been given (p. 53) of 

 these effects, which appear to be due to the formation of a 

 veritable explosive wave, which wave is totally distinct from 

 the sonorous waves, properly so called, since it results from a 

 certain cycle of mechanical, calorific, and chemical actions, which 

 reproduce themselves step by step, transforming themselves one 

 into the other; this is shown in the experiments which the 



1 " Comptes rendus des stances de I'Acad&nie des Sciences," xcv. p. 955. 



2 '" Annales de Chimie et de Physique," 4" se*rie, torn, xviii. pp. 160, 199. 



3 That is, it does not contain any trace of a hydrogenated body susceptible 

 of forming hydrocyanic acid, which, on the contrary, gives rise to equilibrium. 



