CAPTAIN NOBLE AND MR. E. A. ABEL ON EIRED GUNPOWDER. 51 
In 177.8 Dr. Hutton*, of Newcastle-on-Tyne, read before the Royal Society an 
account of his celebrated researches in Gunnery; and in his 37 th tract are detailed the 
experiments from which he deduced the maximum pressure of gunpowder to be about 
twice that given by Robins, or a little more than 2000 atmospheres. 
Hutton, like Robins, saw that the moving force of gunpowder was due to the elas- 
ticity of the highly heated gases produced by explosion; and, upon the assumption that 
the powder was instantaneously ignited, he gave formulae for deducing the pressure of 
the gas and velocity of the projectile at any point of the bore. These formulae, the 
principles of thermodynamics being then unknown, are erroneous, no account being 
taken of the loss of temperature due to work performed ; but we shall have occasion to 
point out that the error arising from this cause is not nearly so great as might be at 
first supposed^. 
In 1797 Count Rumford $ communicated to the Royal Society his experimental deter- 
minations of the pressure of fired gunpowder ; his results, although conjecturally 
corrected by more than one writer, have retained up to the present time their position 
as the standard, if not the only, series of .experiments in which the pressure has been 
obtained by direct observation. 
In prosecuting his remarkable experiments Count Rumford had two objects in view: 
first to ascertain the force exerted by exploded powder when it completely filled the 
space in which it was exploded ; secondly , to determine the relation between the 
density of the gases and the tension. 
The apparatus used by Rumford consisted of a small strong wrought-iron vessel or 
chamber 0-25 inch. (6-3 millims.)' in diameter, and containing a volume of ’0897 cubic 
inch (T47 cub. centim.). It was terminated at one end by a small closed vent filled 
with powder, so arranged that the charge could be fired by the application of a red-hot 
ball ; at the other end it was closed by a hemisphere upon which any required weight 
could be placed. 
When an experiment was to be made, a given charge was placed in the vessel, and a 
weight, considered equivalent to the resulting gaseous pressure, was applied to the 
hemisphere. If, on firing, the weight was lifted, it was gradually increased until it was 
just sufficient to confine the products of explosion, and the gaseous pressure was calcu- 
lated from the weight found necessary. 
The powder experimented with was sporting, of very fine grain ; and as it contained 
only 67 per cent, nitre, it differed considerably from ordinary powder. Its specific gra- 
vity (1-868) and gravimetric density (T08) were also very high; but in his experiments 
Count Rumford appears to have arranged so that the weight of a given volume of gun- 
* Mathematical Tracts, 1812, vol. iii. pp. 209-316. 
f Huttos', in a note to the new edition of Robins’s ‘ Gunnery,’ published in 1805, mentions that the elastic 
force of gunpowder was considered by John Bernoulli to he that of 100 atmospheres, while Daniel Bernoulli 
considered it to he equal to about 10,000 atmospheres. — Robins, loc. cit. p. 57. 
+ Philosophical Transactions, 1797, p. 222. 
H 2 
