1879 -] Proceedings of Societies . 505 
The results given in this table are very striking. Taking the 
two natures of powder which commence and close the list, the 
heat generated by the Spanish powder is about 50 per cent 
higher than that generated by the mining powder, while the 
quantity of permanent gases evolved by the latter is 'about 50 per 
cent greater than that given off by the former. Thus it appears 
that the great inferiority of heat developed by the mining powder, 
as compared, with the Spanish powder, is compensated, or at 
least approximately so, by the great superiority in volume of 
permanent gases produced. A similar relation is observed in 
respedt to the other powders, and it would indeed appear that 
the pressures at any given density and the capacity for per- 
forming work of the various powders are not very materially 
different. This fadt has been entirely verified for the whole of 
the Waltham Abbey powders, and in a less degree for the three 
other powders also. The peculiarities shown by the mining 
powder are so interesting that it appeared important to deter- 
mine its tension when fired under a high gravimetric density. 
11,560 grs. (749 grms.) of this powder have therefore been fired 
under a gravimetric density of unity. The pressure developed 
by two very accordant observations was, when corredted, 44 tons 
on the square inch (6706 atmospheres). The pressure obtained 
under similar circumstances from Waltham Abbey powder was 
43 tons on the square inch (6554 atmospheres), The capacity 
for performing work of the various descriptions of powder was 
also found to be not very different, a similarity of result the 
more remarkable seeing that with, at all events, three of the 
powders there are striking differences both in their composition 
and in the decomposition they experience, and when in conse- 
quence material variations both in pressures at different densities 
and in potential energy might have been expedted. With respedt 
to the great difference in heat evolved by the Spanish and mining 
powders, it appears difficult to resist the conclusion that the 
small number of units of heat evolved by the latter is in great 
measure due to the quantity of heat absorbed in placing the very 
much larger proportion of the produdis of combustion in the 
form of permanent gases. This suggestion would also appear 
fully to explain the fadt alluded to in the authors’ first memoir, 
and to which they had been led purely by experiment, namely, 
“that the variations observed in the decomposition of gun- 
powder do not, even when very considerable, materially affedl 
either its tension or capacity for performing work.” A compa- 
rison between different gunpowders, or a comparison between 
gunpowder and other explosive agents, cannot therefore, as has 
been proposed, be determined by a simple measurement of the 
corresponding units of heat they evolve. As regards the actual 
temperature of explosion, the results of the further experiments 
detailed in this paper leave little doubt that the temperature 
named in the authors’ first memoir, viz., 2200° C., is not far 
VOL. IX. N.S.) 2 L 
