510 POWDEKS WITH A NITBATE BASE. 



This being taken into account, the heat liberated amounts for 

 1 grm. of explosive matter really transformed to 750 Cal., a 

 figure which exceeds by 75 '5 Cal., or by a ninth, the theoretical 

 value 674-5 Cal. 



This excess is evidently owing to the causes just described, 

 and principally to the use of charcoal instead of pure carbon, 

 and to the formation of iron sulphide. The calculation made 

 from the heat of combustion of the weight of pure carbon, as 

 extracted from charcoal, would give 706 Cal., a value which is 

 also too low. But the number 750 Cal. remains below the 

 possible difference, which amounts to 843 Cal., according to 

 what has been said above. For the powders studied by other 

 observers, the effective reaction being unknown, we cannot 

 carry out the thermal work with certainty. The values deduced 

 from our equations generally remain below the figures actually 

 found, which is attributable to analogous causes, and principally 

 to the excess of heat produced by the combustion of the charcoal 

 of powder. This excess will, moreover, vary with the constitu- 

 tion of this charcoal itself, which changes greatly in the different 

 countries and for the different kinds of powder. 



7. Volume of the gases liberated. The uncertainties are less, 

 and consequently the discrepancies between theory and practice 

 more limited for the volume of the gases. For instance, the 

 volume of the gases obtained by Noble and Abel had a mean 

 value of 267 litres, with variations comprised between 285 and 

 232 litres. 



The following table, according to these authors, expresses the 

 volume of the permanent gases produced by the explosion of 

 1 grm. of powder, supposed perfectly dry : 



W.A. pebble powder 278-3 c.c. 



K.L.G., W.A. powder 274-2 



F.G., W.A. powder 263-1 



No. 6, Curtis and Harvey's powder 241-0 



Blasting powder 360-3 ,, 



Spanish spherical 234-2 



Gay-Lussac assigned 250 c.c. 1 at a low pressure. Bunsen and 

 Schiskhoff (sporting powder), 193 c.c. (at a low pressure) ; Linck, 

 218 c.c. (cannon powder) at high pressures ; Karolyi, 209 c.c. 

 (ordnance powder) and 227 c.c. (rifle powder); Yignotti, 231 c.c. 

 to 244 c.c., according to the nature of the charcoal results, 

 the differences of which are attributable to the diversity of the 

 pressures and relative proportions. 



The above formula indicates 300 litres, a figure which would 

 reduce itself to 288 litres were the foreign substances taken into 

 account. The change of a small quantity of carbonic acid into 

 bicarbonate would lower it still more, and bring it nearly to the 

 value found by Noble and Abel. 



1 He gives elsewhere 449*5 cc., owing to some error in copying. 



