510 MM. Bunsen and Schischkoff's Chemical 



may be shown from the calculation of the temperature of flame, 

 that the tension caused by such a volatilization cannot amount to 

 one atmosphere. The temperature of the flame of hydrogen 

 burning in aii- is 3259° C* A bead of powder residue melted 

 on a thin platinum wire volatilized gradually in a jet of hydrogen 

 burning in air, but it never reached ebullition, and hence the 

 tension of its vapour could never have reached an atmosphere. 

 And hence the pressure exerted by the vapour of the solid pro- 

 ducts of decomposition at the temperatures 2993° and 3340° C. 

 can only be infinitely small, and may be safely neglected. It is 

 possible, therefore, to calculate from our experiments the maxi- 

 mum pressure which is reached, but never exceeded, by the com- 

 bustion of powder in a closed space. 



If we call Gp the weight of the powder, Sp its gravimetric t 

 density, G^ the weight of residue obtained from the Gp powder, 

 Sr the density of the residue at 3340° C, and V the volume of 

 gas at 0° C. and 760 millims. obtained from Gp. If, further, / 

 be the temperature of the flame of powder burning in an enclosed 

 space, we obtain, from the following equation, the pressure jj° 



which powder exerts when it burns in the space -^^which it 

 occupies, and which is supposed to be impervious to heat, 

 _ V(l X 000366 X t) 

 ^°~ Gp_G. 



Sp Sr 



In this equation there is only one magnitude whose determi- 

 nation presents any difficulty, that is Sr, or the specific gravity 

 of the fixed powder residue at 3340° C, the temperature of the 

 flame. We have determined this specific gravity by a method 

 not yet published, which one of us has used to determine the 

 volatilization and expansion of rocks melted at high temperatures, 

 independently of the expansion of the vessels containing them. 

 A n experiment according to this method gave, with approximate 

 but sufficient accuracy, for the specific gravity of the residue. 



At 18" C 2-350 



At 2808" C 1-520 



By interpolation for the specific gravity of the residue at 3340° 

 we obtain 8^= 1-50. The values of the magnitudes occurring in 

 the formula are therefore for the powder investigated, 



* Gasometrische Methoden, von R. Bunsen, p. 254. Roscoe's transla- 

 tion, p. 242. 



t This expression is used in artillery to denote the weight of a cubic 

 centimetre of granular powder. 



