288 COMPOUNDS DERIVED FROM NITRIC ACID. 



that for each nitric equivalent fixed on to a carbohydrate, a 

 heat of about -f- 12 Cal., on an average, is liberated. This 

 value, it may be repeated, is double that of the heat of formation 

 of the nitric ethers properly so called. 



4. In order to deduce from this the heat of formation of gun- 

 cotton from its elements, it would be necessary to determine the 

 heat of formation of cotton itself, which is at present unknown. 



5. Messrs. Sarrau and Vieille have measured the heat given off 

 in the decomposition of gun-cotton. As this varies with the con- 

 ditions, they give results for the decomposition that furnishes 

 the foUowing products, 15CO + 9C0 2 -f HH + UN + 9H 2 0. 

 From this we deduce, for the heat of total combustion of gun- 

 cotton 



QM + H 48 + UN + 42 (= 1143 grms.), the value -f 633 Cal. 



On oxidising the gun-cotton by means of ammonium nitrate, 

 they obtained a result leading to + 698 Cal. The discrepance 

 in the two values shows the difficulty of carrying out experi- 

 ments which are of this nature, and are based upon complicated 

 reactions. The above figures may, however, serve as approximate 

 data until the discovery of a more definite method. 



According to the first value, the heat of total combustion of 

 gun-cotton in free oxygen would be 562*5 cal. for 1 grin. 



The heat of formation from its elements would be 624 Cal. for 

 1143 grms. 



6. We will now say a few words about the explosive decom- 

 position of gun-cotton conducted in a closed vessel and at 

 constant volume ; this formed the subject of a carefully studied 

 and very interesting paper by Messrs. Sarrau and Vieille. 1 

 They found that the volume of the gases (reduced to and 

 760 mms.), and also their relative proportion, vary with the 

 density of charge, i.e. with the pressure developed at the 

 moment of the explosion. These are some of the results 



Density of charge ...... 0-01 0*023 0'2 0-3 



Volume of gases (reduced) per 



grm. of material ...... 658-5 670-8 682-4 _ 



/CO 49-3 43-3 37-6 34-7 



Composition of the gases <*> *$ J4-6 27-7 30-6 



per 100 volumes g 127 172 184 17;4 



VCH 4 



0-0 trace 0-6 1-6 



From this table it follows that the quantities of carbonic acid 

 and hydrogen increase with the density of charge ; whereas that 

 of carbon monnade diminishes. We notice, moreover, the pro- 

 duction of an appreciable and increasing quantity of marsh gas. 



1 " Comptes rendus des stances de 1' Acad&nie des Sciences " torn. xc. 

 p. 1058. 



