PRESSURES DEVELOPED. 511 



8. The value of the permanent gases varies nearly inversely 

 with the heat developed in accordance with the equation on 

 p. 499 (see also p. 505), and as is shown by the table below 



Heat disengaged Volume of gases 

 Powder. per gramme of produced per 



powder. gramme of powder. 



Spanish pellet 767-3 Cal. 234-2 cc. 



Curtis and Harvey No. 6 764-4 241-0 



F.G., W.A 738-3 263-1 



R.L.G.,W.A 725-7 274-2 



Pebble W.A 721-4 278-1 



Blasting 516-8 360-3 



9. In general the characteristic product, QV, is nearly con- 

 stant, as the author observed in 1871, for the various powders. 

 Now, this product measures the strength for explosive sub- 

 stances of which the specific heat is the same, which is 

 practically the actual case (p. 34). 



The temperature of the combustion of powder has been 

 estimated by writers on this subject, from rather uncertain 

 tests, at 2200. 



10. The pressures developed during the combustion of powder 

 at constant volume have been observed by Noble and Abel 

 with the aid of the crusher. The following are their numbers : 



Powder. 

 Density of charge^ 



0-1 

 02 

 0-3 

 0-4 

 0-5 

 0-6 

 07 

 0-8 

 0-9 

 1-0 



These results may be represented, according to these authors, 



2193 2460 ' 



by the empirical formula, -, or - , formulae in 



n U'bo n U'b 



which they suppose that the products which are not gaseous 

 at the temperature of the explosion occupy 0*68 c.c., or, more 

 simply, 0'6, the same volume being calculated at the ordinary 

 temperature. 



The theoretical formula on p. 499 gives pressures nearly the 

 same as the above for high densities of charge (1*0 and 0'9) ; 

 below which it gives results which are too high, amounting to 

 double the numbers found for the density 01. This difference 

 increases as the pressure diminishes; it may be connected 

 with the increase of dissociation. 



