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CAPTAIN NOBLE AND ME. E. A. ABEL ON EIEED GUNPOWDER. 
through 2 0- 694 C., or 1 gramme of the charge, in burning, communicated to the gun 
89 - 4 gramme-units of heat. 
Considering the difficulty, in an experiment of this nature, of avoiding a considerable 
loss from radiation, conduction, and other causes, we do not think we shall be far wrong 
in assuming that in the case of the 12 pr.-B. L. gun, fired under the conditions named, 
the heat communicated to the gun is about 100 gramme-units for each gramme of powder 
exploded. 
To arrive at the amount of heat communicated to the gun w T hen still larger guns are 
employed, there are two principal points to be considered — 1st, the ratio which the 
amount of the surface bears to the weight of the charge exploded ; and 2nd, the time 
during which the cooling effect of the bore operates upon the products of explosion. 
The first of these data is of course exactly known, and from our experiments the 
second is also known with very considerable exactness. Computing, therefore, from 
the data given by the 12-pr., the loss of heat suffered by the gases in the 10-inch gun, 
we find that loss to be represented by about 25 gramme-units ; and hence we find that the 
quantity of work in the form of heat communicated to the gun varies approximately from 
250 gramme-units per gramme of powder in the case of a rifled musket, to 25 gramme- 
units in the case of a 10-inch gun. 
Similar considerations lead us to the conclusion that in a close vessel such as we 
employed for explosion, when filled with powder , the loss of pressure due to the com- 
munication of heat to the envelope would not amount to 1 per cent, of the total pressure 
developed. 
Y. PRESSURE IN THE BORES OF GUNS, DERIYED FROM THEORETICAL CONSIDERATIONS. 
We now pass to the theoretical consideration of the question. Suppose the powder 
to be fired, as is the case in the chamber of a gun, and suppose, further, that the products 
of combustion are allowed to expand, what will be the relation between the tension of 
the gases and the volume they occupy throughout the bore \ 
For the sake of simplicity, we shall, in the first instance, assume that the gravimetric 
density of the powder is unity, that the powder fills completely the space in which it 
is placed, that the whole charge is exploded before the projectile is sensibly moved 
from its initial position, and that the expansion takes place in a vessel impervious to heat. 
In our preliminary sketch we alluded to the results of Hutton’s investigations as to 
the relations existing between the density and tension of the gases and the velocity of 
the projectile at any point of the bore. Hutton, however, assumed that the tension of 
the inflamed gases was directly proportional to their density, and inversely as the space 
occupied by them. In other words, he supposed that the expansion of the gases, while 
doing work both on the projectile and on the products themselves, was effected without 
loss of heat. 
Eecent research, which has demonstrated that no work can be effected by the expan- 
sion of gases without a corresponding expenditure of heat, has enabled modern artillerists 
