CAPTAIN NOBLE AND MR. F. A. ABEL ON FIRED GUNPOWDER. 231 
Waltham Abbey powder, the agreement is very close ; the departure from the normal 
curve not in any case exceeding that obtained in particular experiments with the 
Waltham Abbey powders themselves. 
With respect to the pressure given by mining powder, the peculiarities shown by 
this powder were so interesting that it appeared to us important to determine its 
tension when fired under a high gravimetric density. We accordingly fired (ex¬ 
periment 230) 11,560 grs. (749 grms.) of this powder under a gravimetric density of 
unity. 
The pressures developed by two very accordant observations was, when corrected, 
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). 
It will afterwards be seen that the capacity for performing work of the various 
descriptions of powder is also not very different, and this similarity of result is the 
more remarkable when it is remembered that with, at all events, three of the powders, 
there were striking differences both in their composition and in the decomposition 
that they experienced, and when, in consequence, material variations both in pressures 
at diff erent, densities and in potential energy might have been expected. 
But returning to the great difference in heat evolved, for example, by the Spanish 
and mining powders, we think it is 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 that has been absorbed in placing the very much larger proportion of the 
products of combustion in the form of permanent gases. This suggestion would, we 
think, also fully explain the fact alluded to in our first memoir,'" and to which we 
had been led purely by experiment, namely, “ that the variations observed by us in 
the decomposition of gunpowder do not, even when very considerable, materially 
affect either its tension or capacity for performing work.” 
The above facts and remarks would also show that a comparison between different 
gunpowders, or a comparison between gunpowder and other explosive agents cannot, 
as has been proposed,! be determined by a simple measurement of the corresponding 
units of heat they evolve. 
Did such a law hold, the Spanish powder should have more than 50 per cent, 
advantage over the mining powder, but as a matter of fact, although not very widely 
different, the mining powder had the advantage both in respect to the tension observed 
in a close vessel and to the energy developed in the bore of a gun. 
As regards the actual temperature of explosion, we have little doubt, from the 
results of the further experiments detailed in this paper, that the temperature named 
in our first memoir, viz., 2200° C., is not far removed from the truth for the principal 
powders with which we were then experimenting. 
* Loc. cit., p. 88. 
t De Tromenec, ‘ Comptes Reudus,’ tom. lxxvii., p. 128. 
