102 
CAPTAIN NOBLE AND ME. P. A. ABEL ON EIEED GUNPOWDEE. 
Or, stating the results per gramme of powder, it appears that in the several experi- 
ments the solid products arising from the combustion of a gramme of powder occupied 
respectively -3105, -2731, -3125, -2987, -2869, -2894, *2726, and -2810 cub. centim. 
The mean of these figures is *2906 ; and we may thence conclude that at 0°C. the 
solid residue of 1 gramme of burned powder occupies a volume closely approximating to 
•29 cub. centim. ; therefore, since the solid products represent 57 percent, of the original 
weight of the powder, it follows that at 0° C. the specific gravity of the residue is 
about 1*4. 
N. PEESSTJEE IN CLOSE YESSELS, DEDUCED FEOM THEOEETICAL CONSIDEEATIONS. 
From the investigations we have described, it appears that in a close vessel, at the 
moment of explosion, or at all events shortly afterwards, the results of the decompo- 
sition of a given charge (say 1 gramme) of powder such as we have experimented with 
are as follows : — 
1. About 43 per cent, by weight of permanent gases, occupying, at 0°C. and under a 
pressure of 760 millims., a volume of about 280 cub. centims. 
2. About 57 per cent, by weight of liquid product, occupying, when in the solid form 
and at 0°C., a volume of about - 3 cub. centim. 
Now, if we assume that the conditions known to exist shortly after explosion obtain 
also at the moment of explosion, we are able, with the aid of our experiments, to com- 
pute the pressure, temperature of explosion, and volume occupied by the permanent 
gases. We propose to make these calculations, and then, by comparison with the 
results obtained under the varied conditions adopted in our experiments, to form an 
estimate of the correctness of our assumption. . And, first, to establish a relation between 
the tension and the mean density of the products of explosion at the moment of 
ignition, — 
Let A B C D, Plate 15. fig. 4, represent the interior of the vessel, of volume v, in 
which the experiments were made. Let C D E F represent the volume of a given 
charge of powder placed in the vessel. Let & be the ratio which the volume CDEF 
bears to A B C D, and let C D H G (vul suppose) be the volume occupied by the liquid 
products at the moment and temperature of explosion. 
It is obviously, for our present purpose, a matter of indifference whether we suppose 
the liquid products collected, as in the figure, at the bottom of the vessel or mixed with 
the permanent gases in a finely divided state. 
Our conditions on explosion, then, are: — we have the space C D H G=y occupied 
by the fluid residue, and the space A B IL 0=^(1 — «£) by the permanent gases. 
Hence, since the tension of the permanent gases will vary directly as their density, we 
have, if jp represent the pressure and D the density, 
^=RD, 
where R is a constant. 
( 1 ) 
