The Typical Cellulose and the Cellulose Gfoup 43 



process, it has been ascertained that the heat liberated is 11-12 

 cal. per unit of HNO 3 reacting. This 'heat of formation' 

 is approximately equal to that which is observed in converting 

 starch into the corresponding nitrates. 



HEAT OF COMBUSTION. The total combustion of gun 

 cotton by free oxygen evolves heat equal to 2,300 cal. (H 2 O of 

 combustion liquid), or 2,177 ca ^- w i tn tne H 2 O as gas or vapour, 

 per i grm. of the compound. Collodion cotton gives the corre- 

 sponding numbers 2,627-2,474 cal. ; gun cotton exploded in 

 confined space gives 1,071 cal. (H 2 O of combustion liquid). 



PRODUCTS OF COMBUSTION of gun cotton exploded in a 

 closed vessel vary in relative amount and in composition 

 with the 'density of the charge,' or the pressure developed 

 at the moment of explosion. Thus the CO 2 and H increase 

 with the density of charge ; the CH 4 also, but, being present in 

 very small ratio (o'o-i*6 p.ct. maximum), it may be neglected. 

 The following equations may be taken as fairly representing 

 the combustion of 2C24H 18 O 9 (NO3H) U , under varying con- 

 ditions : 



Density of charge 



o-oio . . . 33CO + i5CO 2 + 8H 2 + 2iH 2 



0-023. 3oCO + i8CO 2 +iiH 2 +i8H 2 



0-200. . . 



0-300. . . 



Under the ordinary conditions of explosion in firearms with 

 maximum density of charge, the quantities of gas produced 

 approximate more and more closely to the limit : 



2 4 CO + 24CO 2 + i7H 2 + i2H 2 O + nN 



Under ' explosion,' it will be seen that no nitric oxide or 

 other nitrous gases are formed ; but when a slower combustion 

 takes place, with the products of combustion escaping freely 



