CAPTAIN NOBLE AND MR. E. A. ABEL ON EIRED GUNPOWDER, 
95 
centims. of the mixed gases, and the total quantity of gas generated by a gramme of 
powder (282 cub. centims.) would become 353 cub. centims. 
On the other hand, the *28 gramme of C0 2 contains ‘0764 grm. C., which, burnt to 
C0 2 , gives rise to 611 gramme-units, or burnt to CO gives rise to 187 gramme-units. 
Now if a given weight of carbonic oxide, in combining with another atom of oxygen 
and burning to carbonic anhydride, generates 424 units of heat, it is obvious that the 
reverse process, or dissociation of the carbonic anhydride into carbonic oxide and oxygen, 
must absorb precisely the same amount of heat. 
Hence the dissociation we have supposed would absorb 424 gramme- units of heat, 
and the consequent loss of temperature would reduce the pressure in a degree that 
would far more than compensate for the increment due to the increase of volume by 
dissociation. 
K. TENSION OP FIRED POWDER OBSERVED IN A CLOSE VESSEL. 
As it Avas one of our principal objects to determine with as much accuracy as possible 
not only the tension of fired gunpowder Avhen filling completely the space in which it 
was exploded, but also to determine the law according to which the tension varied with 
the density, it has been our endeavour to render both varied and complete the experi- 
ments instituted to ascertain these important points. 
In the first experiments described in this paper, as well as in the earlier series which 
formed the basis of Captain Noble’s lecture delivered to the Royal Institution, the 
method adopted to determine the variation of pressure was as follows : — The space in 
which the powder was to be fired having been carefully established, the weight of the 
powder to be experimented with which would accurately fill the space was ascertained, 
and -j^-, &c. of the vessel was successively filled with powder, which Avas then 
fired, and the resulting pressures determined. 
Later on it was found that, as with each description of powder the gravimetric density 
varied, it was more convenient to refer the pressure not, as at first, to a density arrived 
at by taking the weight of powder which completely filled a given space as unity, but 
to the specific gravity of water as unity. The densities given hereafter must therefore 
be taken to represent the mean density of the powder inclusive of the interstitial spaces 
between the grains, or, what is the same thing, the mean density of the products of 
explosion referred to water as unity. The gravimetric density of the modern pebble 
powders closely approximates to 1 * ; that of the old class of cannon-powders, such as 
L. G., R. L. G., &c., varied generally betweenf '870 and *920; that of F. G. and 
sporting-powders was still lower. 
* This statement applies only to the powder taken in considerable bulk. In our explosion-vessels, the gravi- 
metric density, when they were completely filled, did not exceed, with pebble powder, ‘92 or '93. The state- 
ment, therefore, that the powder was fired in so many per cent, of space does not actually refer to the space 
occupied in the chamber, but to a chamber of a size that would hold powder of our standard density. 
f Boxer, Gen., R.A., ‘Treatise on Artillery,’ 1859, p. 21. Mordecai, Major, U.S.A., ‘Report on Gunpowder,’ 
Washington, 1845, p. 187. 
