130 
CAPTAIN NOBLE AND MB. E. A. ABEL ON EIEED GTJNPOWDEB. 
The results of Table XVIII. are graphically represented in Plate 24 ; and on the 
axis of abscissae are figured, for convenience, both the density of the products and the 
volume they occupy. 
The curve marked A represents the tensions deduced (with a slight correction for loss 
of heat) from actual observation in a close vessel, and may, as we have already said, be 
taken to represent the pressures that would exist were the products of combustion 
allowed to expand in a vessel impervious to heat and without production of work. 
The curve marked B, derived from equation (30), denotes the tensions that would exist 
in the bore of a gun, if we suppose the powder, of a gravimetric density =1 and filling 
entirely the chamber, to be completely consumed before the projectile is moved from 
its place, and to expand in a gun impervious to heat. By comparison with the Curve A 
will be seen the difference in tension arising from the loss of heat due to the work 
expended. The great importance of the heat contained in the non-gaseous portion 
of the charge is rendered apparent by comparison of Curve B with Curve 4, Plate 23, 
or Table XVII., where, on Bunsen - and Schischkoff’s hypothesis, the permanent gases 
are supposed to expand without deriving any heat from the non-gaseous portion of the 
charge. 
The area comprised between Curve B and the axis of abscissae represents the maxi- 
mum work that it is possible to obtain from powder. 
Curve C represents the mean results obtained with It. L. G. powder from the 8-inch 
and 10-inch guns, and Curve D represents the mean results obtained with pebble powder 
from the 10-inch and 11-inch guns. 
It is interesting to study the differences exhibited by these curves B, C, and D. The 
Curve C, representing the pressures obtained with It. L. G., denotes tensions not far 
removed from the theoretic curve, while the densities are still very high ; before the 
volume is much increased, the two curves slide into one another and become almost 
coincident. 
The Curve D, on the other hand, is at first very considerably below both the E. L. G. 
and the theoretic curve. It is still considerably lower even when the E. L. G. curve is 
practically coincident with the theoretic curve, and it retains a measurable though slight 
inferiority of pressure even up to the muzzle of the gun. 
These differences are without doubt due to the fact that with the E. L. G. powder, 
at least under ordinary circumstances, the whole or a large proportion of the charge 
is consumed before the projectile is greatly removed from the seat of the shot. With 
the slower-burning pebble powder, on the other hand, a considerable quantity of powder 
remains unconsumed until the projectile approaches the muzzle; and the curve indicates 
in a very striking way the gradual consumption of the powder, and the portion of the 
bore in which the slow-burning powder may be considered practically burned. 
It might perhaps be expected that the difference between the theoretic Curve B and 
the observed Curves C and D near the muzzle would be greater than is shown, since the 
Curve B has been obtained on the supposition that the expansion has taken place in a 
vessel impervious to heat. 
