284 COMPOUNDS DERIVED FROM NITRIC ACID. 



According to the preceding data, the formation of a nitric 

 ether, by means of alcohol and nitric acid, would give off, on an 

 average, -h 5 Cal. for each equivalent of fixed nitric acid. This 

 quantity may be used to calculate the heat of formation and 

 the heat of combustion of nitric ethers that have not as yet been 

 studied. 



2. Let us suppose an ether to be formed from an alcohol, 

 represented by the letter K ; the ether being 



K + fiHN0 3 - 7&H 2 0. 



The heat of formation of the ether from its elements will be 

 deduced from the heat of formation, A, of the alcohol by the 

 following formula: 



A -f 41-671 -f 5n - 697i = A- 22'4n. 



It is lower than the heat of formation of the original body ; 

 a fact which distinguishes ethers from nitro-compounds (p. 276), 

 the heat of formation of which, on the contrary, exceeds that of 

 the original substance by + $n Cal. The difference, which is 

 31 '4 Cal. for each equivalent of fixed nitric acid, denotes the 

 excess of energy of a nitric ether over that of an isomeric nitro- 

 derivative, formed from the same original substance ; benzyl 

 nitrate, for instance, as compared with nitrobenzyl alcohol. 



3. The heat of decomposition of a nitric ether can thus be 

 calculated a priori, if its products be known ; as in the case in 

 which the substance contains an excess of oxygen. 



4. The heat of total combustion of a nitric ether is deduced in 

 all cases from that of the original alcohol. This being equal to 

 Q, the formula of the ether deduced from n equivalents of nitric 

 acid will contain riH. less, and its heat of combustion will be 



Q - 34-5/1 -f 22-4^ = Q - 12'ln. 



If, for example, we take nitroglycerin (n = 3), we shall get 

 Q = 392'5 Cal., according to M. Louguinine's data for glycerin. 

 The heat of total combustion of nitroglycerin, calculated by 

 the formula, will then be -f- 356-2. Messrs. Sarrau and Vieille 

 found by experiment, + 360*5. The discrepancy amounts to 

 one-hundredth, and includes both the error made in the heat 

 of combustion of glycerin and also that of nitroglycerin. 



5. In order to make these points clear, let us calculate, accord- 

 ing to the above formula, the formation of methyl nitrate 



C + H 3 + N + 3 = CH 2 (HN0 3 ). 



The formation of methyl alcohol from its elements, A, = 62 ; we 

 shall therefore get + 39 '6 for the formation of methyl nitratefrom 

 the elements. 



The heat of total combustion of this ether will be 



+ 157-9 for 77 grms., or 2050 cal. for 1 grm. 



