502 POWDEKS WITH A NITRATE BASE. 



7. These figures would be appreciably modified if we 

 assumed, as was formerly done, the total vaporisation of the 

 saline compounds at the moment of the explosion, which would 

 increase the volume of the gases by a fourth, while slightly 

 diminishing the heat liberated. But this hypothesis appears 

 to be abandoned by nearly all specialists at the present day. 

 It might, however, be true for potassium sulphide, a body 

 which is volatilised at a red heat. It should further be 

 observed that the theoretical temperature is too high, as in 

 all calculations of this kind, owing to dissociation and the 

 variation in the specific heats with the temperature. This 

 tends to lower the theoretical pressure. But there is, as we 

 have said elsewhere (p. 11), a certain compensation, due to 

 the fact that in greatly compressed gases the variation of 

 pressure with temperature is far smaller than would be indicated 

 by Mariotte's and Gay-Lussac's laws. All these remarks apply 

 equally to the other equations above set forth, and which we 

 are about to discuss. 



8. If the substance used contained a certain proportion of 

 sulphur in excess and this sulphur were changed into iron 

 sulphide (p. 497), 11 '9 Cal. should be added per equivalent of 

 iron sulphide. The heat liberated will therefore be increased. 

 This increase represents one-eighth of the heat liberated ; but 

 the increase in the relative weight for an equivalent of sulphur 

 is nearly the same, which forms a compensation for the same 

 weight of matter. 



These observations are equally applicable to the other 

 equations. 



9. Equation (2), 



4KN0 3 + 5C = 2K 2 C0 3 + 3C0 2 + 4N, 



represents 116 grms. of matter, or, for 1 kgm., 129 grms. of 

 carbon and 878 grms. of nitre. The products being, 593*6 grms. 

 C0 3 K 2 , 284-5 grms. C0 2 , 120-5 K 



The reaction liberates + 901 Cal. at constant pressure, or 90'8 

 CaL at constant volume; or, for 1 kgm., 777 Cal. at constant 

 pressure, or 783 Cal. at constant volume. 



The reduced volume of the gases = 27'9 litres ;' or, for 1 kgm., 

 240-5 litres. 



Permanent pressure = ', with the usual reservation. 



n O'At 



Theoretical temperature = 3982. 



T , , . , 3749 atm. 

 Ineoretical pressure = . 



