CAPTAIN NOBLE AND MR. E. A. ABEL ON FIRED GUNPOWDER. 
99 
the powder entirely fills the space in which it is fired, or, indeed, whenever it occupies 
a considerable percentage of that space. But though the pressure may not be seriously 
affected when the generated gases are of a high density, it is more than probable 
that some very appreciable correction should be made in the results we have observed 
when experimenting with gases of low density. In this latter case the cooling influence 
of the vessel would be greatly increased, not only from the higher ratio which the cooling- 
surface bears to the charge, but also from the slowness of combustion due to the com- 
paratively feeble pressure ; and we think the effect of slow combustion is clearly traceable 
in the low tensions observed with pebble powder (see curve, Plate 16) at densities of 
*1, -2, and -3, as compared with those given at corresponding densities by F. G. powder, 
the combustion of which would be much more rapid. But we shall return to this point 
when we compare our results with those demanded by theory. 
Upon the same Plate (Plate 13) on which we have given curves representing the 
experiments of Bumford and Hodman, there is also laid down a curve representing our 
own experiments. The very high results obtained by Bumford are probably in great 
measure attributable to his method of experiment. The charges being placed at one 
end of his little vessel, while the weight to be lifted, so to speak, closed the muzzle, the 
products of combustion acquired a high vis viva before striking the weight, and thus 
indicated a much higher pressure than that due to the tension of the gas, just as in 
Bobins’s well-known experiment a musket-barrel may be easily bulged or burst by a 
bullet placed at some distance from the charge. That Bumford’s and even Piobert’s 
corrected estimate of the tension of fired gunpowder was very excessive is of course 
indisputably proved by our experiments, as the vessels in which they were made were 
quite incapable of resisting pressures at all approaching those assigned by these eminent 
authorities. 
Bodman’s results are also too high, from a defect in the application of his system of 
measurement, which has elsewhere * been pointed out; and his experiments on the ratio 
of tension to density were not carried sufficiently far to admit of comparison in the 
more important portion of the curve. 
L. DETERMINATION OF HEAT GENERATED BY THE COMBUSTION OF GUNPOWDER. 
The amount (that is the number of units) of heat liberated by the combustion of 
gunpowder is determined from experiments Nos. 46, 47, 48, 49, and 63. 
The powder used was the B. L. G. and F. G. ; but as it was found that there was 
no material difference in the heat liberated, we have drawn no special distinction 
between the experiments made with the two brands. 
In each of the experiments Nos. 46, 48, and 63, 3800 grains (246-286 grms.) were 
exploded ; and when the necessary reductions were made to convert the alterations in 
temperature which were observed into their equivalents in water, it was found that in 
experiment 48 the explosion of 246-286 grms. F. G. was sufficient to raise 173,077*4 
* Noble, loc. cit. p. 25; Revue Scientifique, No. 48, p. 1138. 
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