66 DURATION OF EXPLOSIVE REACTIONS. 



nitrate, 1 which at a high temperature resolves itself into nitrogen 

 and water. Therefore we definitely obtain 



2NO + + 2H 3 N = 4N + 3H 2 disengages (water, gaseous) 



+ 98,000 cal. 



Every portion of nitric oxide destroyed by the spark with the 

 formation of free oxygen, determines, therefore, a new reaction 

 which disengages heat, and easily propagates the combustion of 

 the system, which does not take place in gases which do not 

 exercise a special reaction on nitric peroxide. 



9. DECOMPOSITION OF ENDOTHEKMAL COMBINATIONS, 

 ACETYLENE, CYANOGEN, ETC. 



1. So far, we have treated more especially of the combustion 

 and detonation of mixtures and combinations containing such 

 combustible elements as carbon, hydrogen, sulphur, and the com- 

 bustive elements such as oxygen. But as the theories which we 

 are considering are based essentially on the disengagement of 

 heat and the development of the gases produced by transforma- 

 tion, they lead to consequences of a very special character, which 

 are very interesting as regards the decomposition of endothermal 

 combinations such as acetylene, cyanogen, and nitric oxide. 



Acetylene, cyanogen, and nitric oxide are, in fact, formed 

 from their elements with the absorption of heat. This absorp- 

 tion amounts to 



A -61,100 cal. 2 for acetylene (C 2 H 2 = 26 grms.) 

 A - 74,500 cal. for cyanogen (2CN = 52 grms.) 

 A -31 ,600 cal. for nitric oxide (NO = 30 grms.) 



If we succeed in rapidly decomposing these gases into their 

 elements, such a quantity of heat reproduced inversely will 

 raise the temperature up to 3000 in acetylene and nitric oxide, 

 up to 4000 in cyanogen, according to a calculation founded on 

 known specific heats of the elements. 



The proper figures for this calculation are as follows. We 

 will admit for the mean specific heat of carbon C 2 = 24 grms., 

 the value 12 ; for that of hydrogen H 2 = 2 grms., 6'8 at constant 

 pressure, and 4'8 at constant volume, these latter values being 

 equally applicable to nitrogen N 2 = 28 grms., and to oxygen 

 2 = 32 grms. at the same volume. We thus find, 



For acetylene decomposed under constant pressure 3300, 

 under constant volume 3640. 



For cyanogen decomposed under constant pressure 3960, 

 under constant volume 4375. 



1 See author's remarks, "Annales de Chimie et de Physique," 5 9 sdrie, 

 torn. vi. p. 208. 



2 This figure refers to carbon as diamond ; in amorphous carbon such as is 

 precipitated at the time of decomposition we should obtain 6000 cal. less. 

 The same remark applies to cyanogen as the mean specific heat of carbon. 



