282 COMPOUNDS DEBITED FROM NITRIC ACID. 



was contained in a little capsule, accurately weighed, and poured 

 drop by drop into the middle of the nitrosulphuric mixture. 

 When a sufficient quantity of glycerin had been poured out 

 the capsule was re-weighed ; the loss in weight showed the 

 quantity of glycerin introduced. 



2. All necessary calculations having been made, it was found 

 that the ordinary reaction, i.e. the case in which the substances 

 are taken in their actual condition 



C 3 H 8 3 + 3HN0 3 = C 3 H 2 (HN0 3 ) 3 + 3H 2 0, 



gives off + 14'7 ; or -f 4*9 for each equivalent of acid that has 

 entered into combination. 



These figures, which are rather below those obtained for nitric 

 ether, show that both the acid and the glycerin have preserved 

 almost all their reciprocal energy throughout the reaction, a 

 circumstance which explains the remarkably easy decomposition 

 of nitroglycerin and the formidable effects thereof. 



3. Again, we find that 



C 3 H 8 3 (in solution) + 3HT0 3 (diluted) = C 3 H 2 (HN0 3 ) 3 (pure) 

 -f 3H 2 (liquid), absorbs - 8'8, or - 2-9 X 3. 



Therefore we have thermal inversion, arising from the solution 

 of the substances ; exactly as in the case of nitric ether. This is 

 another point of resemblance between nitroglycerin and ethers 

 formed from organic oxy-acids. 



4. The heat of formation of nitroglycerin from its elements may 

 be calculated from its heat of formation, as deduced from the 

 heat of combustion which was observed by M. Louguinine. We 

 thus find 



C e (diamond) + H 5 + N 3 + 9 gives off + 98 Cal. for 227 grms., 

 or 432 cal. for 1 grm. 



5. The heat of total combustion and the heat of complete decom- 

 position are, in this case, interchangeable terms, since nitro- 

 glycerin contains an excess of oxygen 



i[2C 3 H 2 (HN0 3 ) 3 = 6C0 2 + 5H 2 + 3N 2 + 0]. 



Sarrau and Vieille have verified the reality of this reaction. 



From the preceding data, we find that the heat of combustion 

 is equal to + 356'5 Gals., or, for 1 grm., 1570 cal. 



Sarrau and Vieille obtained -f 360 '5 Cal. ; a value agreeing 

 as nearly as could be expected. 



Nitroglycerin is decomposed differently if it is ignited as 

 dynamite, i.e. an intimate mixture of silica and nitroglycerin, 

 and if the gases which are formed are allowed to escape freely, 

 under a pressure nearly equal to that of the atmosphere. Sarrau 



1 "Comptes rendus des stances de I'Acad&nie des Sciences" torn, xciii. 

 p. 270. 



