DECOMPOSITION OF ENDOTHERMAL COMBINATIONS. 67 



For nitric oxide decomposed under constant pressure 3200, 

 under constant volume 4500. 



It is understood that the calculation of these temperatures is 

 subordinate to the presumed constancy of the specific heats. 

 Whatever opinion is held in this respect it is certain that it 

 gives an idea on temperature more probable in the present case, 

 where it is a question of an elementary decomposition, than in 

 reactions in which compound bodies are formed, such as in the 

 combustions of hydrogen or carbonic oxide, combustions which 

 are limited in their progress by the dissociation of compound 

 bodies. 



2. However, it has not been possible up to the present to 

 effect the explosion of acetylene, or cyanogen, or of nitric 

 oxide. 



Whereas hypochlorous gas detonates under the influence of 

 slight heat, when in contact with a flame, or a spark, in spite 

 of the smaller amount of heat liberated, + 15,200 cal. (for 

 C1 2 = 87 grms.), which can only raise the elements of this gas 

 to '1250, on the other hand, acetylene, cyanogen, and nitric 

 oxide do not detonate either by simple heating or by contact 

 with flame, nor even under the influence of the spark or even 

 the electric arc. 



These differences are important. The diversity which exists 

 between the mode of destruction of endothermal combinations 

 is due in each given reaction to the necessity of a kind of pre- 

 paration, and a certain amount of preliminary work. The 

 author has, besides, examined l the characters and the generality 

 of this preliminary work in the production of chemical re- 

 actions. Now the work necessary for resolving the compounds 

 named into the elements does not appear to consist in a simple 

 heating, slow and progressive in its nature, at least within the 

 limits of the temperature above pointed out. In fact, acetylene, 

 cyanogen, and nitric oxide never explode, as far as the author's 

 experience goes, no matter to what temperature they are raised. 



It is not that these compound gases are absolutely very 

 stable they in fact decompose frequently, and even according 

 to experience at a dull red heat, either with the formation of 

 polymers (benzene by acetylene), or with a fresh distribution of 

 their elements (nitrogen, monoxide, and nitric peroxide, by 

 nitric oxide) 2 but they do not explode in spite of the very great 

 liberation of heat accompanying these changes, probably by 

 reason of the slowness of their action, nor do they explode, 

 which is stranger still, under the influence of electric sparks, in 

 spite of the excessive and sudden heat which these latter develop. 

 Carbon, however, on the passage of the sparks, is precipitated at 

 once from acetylene or cyanogen, while hydrogen and nitrogen 



1 " Essai sur la M^canique Chimique," torn. ii. p. 6. 



2 " Annales de Chimie et de Physique," 5" srie, tom. vi. p. 198. 



F 2 



