60 DURATION OF EXPLOSIVE REACTIONS. 



friction, remains absolutely powerless with gun-cotton. Now 

 nitrogen chloride is precisely one of the explosive bodies of 

 which we are treating here, which develop the least heat con- 

 sequently the least work, for a given weight, owing to the high 

 figure of the equivalent of chlorine. We therefore see that it is 

 necessary to use more of it by way of priming. As to nitrogen 

 iodide, according to the analogies taken from iodo-substitution 

 compounds, 1 and from the great weight of the equivalent of 

 iodine, its explosion should develop much less heat and much 

 less work for the same weight than even nitrogen chloride ; its 

 impotence is therefore easily understood. 



8. COMBUSTION EFFECTED BY NITRIC OXIDE. 



It is advisable to consider here the conditions which deter- 

 mine the commencement of reactions, conditions which are of 

 fundamental importance in the study of explosive substances 

 and on the knowledge of which the study of the combustion 

 effected by nitric oxide throws a very special light. 



1. Nitric oxide contains more than half its weight of oxygen, 

 and this oxygen, in connection with a combustible body, disen- 

 gages 21,600 cal. more than free oxygen (0 = 16 grm.). It there- 

 fore seems that nitric oxide should be a more active burning 

 agent than free oxygen. Nevertheless, this only happens under 

 peculiar circumstances, noticed by chemists from the commence- 

 ment of the nineteenth century, which have given rise to 

 experimentSj which are produced in every course of lectures, 

 but have not as yet been properly explained. The author has 

 resumed this study, which appears to throw a good deal of light 

 on the work which precedes reactions, and on the manifold 

 equilibriums of which one and the same system is susceptible. 



2. Let us place in the presence of free oxygen two gases sus- 

 ceptible of combination with it, in the same proportions of 

 volume, such as nitric oxide and hydrogen previously mixed in 

 equal volumes, N0 2 + H 2 4- 2 , nitric peroxide is immediately 

 formed, hydrogen being unaffected (respecte). This preference 

 is manifested, evidently, owing to the inequality of the initial 

 temperature of the two reactions, nitric peroxide being formed 

 in the cold ; whereas water is produced only at about 500 to 

 600. 



3. Nevertheless, this explanation is less decisive than it 

 appears to be, since the combination of nitric oxide and hydro- 

 gen liberates a great quantity of heat (1900 cal.), say two- 

 thirds of the heat of formation of gaseous water (29,500 cal.). 

 Now this heat should raise the temperature of the system to the 

 degree at which oxygen and hydrogen combine. 



In order fully to demonstrate the phenomenon, the experi- 

 1 " Annales de Chimie et de Physique," 4* srie, torn. xx. p. 449. 



