268 COMPOUNDS DERIVED FROM NITRIC ACID. 



circumstance which enables the reaction to commence and 

 continue with greater vigour. Thus the explosives which they 

 form act with greater violence. But their useful effects, as 

 regards both work and pressure, are much less, even in the case 

 of silver oxide, which is so easily decomposed, and of mercuric 

 oxide, which, on the other hand, furnishes a gaseous metal. 



10. We will conclude with one remark. When the explosive 

 substance is an acid, such as picric acid, its salts, already 

 existing as such, will produce a less useful effect than 

 simple mixtures of picric acid and metallic oxide; for their 

 formation involves, at the moment of the union of the acid with 

 the oxide, a liberation of heat, i.e. a loss of energy. But, on the 

 other hand, simple mixtures will be more dangerous, less stable, 

 and also subject to spontaneous explosions, owing to the possible 

 combination of the acid with the metallic oxide. 



11. We have just calculated the heat of formation of a 

 nitrated derivative, supposing that of the generator to be known. 

 Conversely, if we know the heat of formation of a nitrogenous 

 body from its elements, together with that of nitric acid and 

 water, and also the heat disengaged in the reaction of the 

 nitric acid on the original generator of the nitrogenous body, 

 the heat of formation of this original generator can itself be 

 calculated. We may observe that this method is less direct 

 than the immediate combustion of the last compound ; therefore 

 the results are less exact They are, however, useful as 

 checks. 



12. Such are the general conclusions that can be deduced 

 from the measurement of the heat disengaged by the combina- 

 tion of nitric acid with organic compounds. These having been 

 given, the experiments of the author, dating from 1871, will 

 now be described. 



First of all, it will be remembered that the action of nitric 

 acid on organic substances gives rise to compounds of two dis- 

 tinct kinds, formed according to a similar equation and with a 

 similar separation of the elements of water ; the one kind con- 

 sists of true ethers, capable of being decomposed by alkalis 

 with regeneration of nitric acid and alcohol, whereas the other 

 kind, designated specially by the name of nitro- compounds, can 

 no longer be split up by distinct reactions, so as to reproduce 

 the generating substances, which are, in the most simple cases, 

 nitric acid and a hydrocarbon. The cause for this difference of 

 reactions will be explained later on. The ethers themselves 

 are divided into two groups, according to whether they are 

 formed from true alcohols, simple in their function, or from 

 alcohols of mixed function, such as cellulose, or condensed ether, 

 derived from several molecules of glucose, which is itself an 

 aldehydic alcohol. 



The heat of formation of several bodies belonging to these 



