CAPTAIN NOBLE AND ME. E A. ABEL ON FIEED GUNPOWDER, 
131 
We have pointed out, however, that although in muskets and small arms the loss of 
heat arising from communication to the bore is very considerable, it is comparatively 
unimportant in very large guns. In our calculations also we have taken X, the specific 
heat of the non-gaseous portion of the charge, at its mean value. It should, however, 
be taken at a higher value, since the specific heat must increase rapidly with the 
temperature ; and this difference no doubt more than compensates for the loss of heat to 
which we have referred as not being taken into account. 
Our hypothesis as to a portion of the charge remaining unconsumed until the pro- 
jectile approaches the muzzle, is confirmed by the well-known fact that in short guns, or 
where powder of high density or very large size is employed, considerable quantities 
sometimes escape combustion altogether. 
The appearance of pellet or pebble powder which has been ignited and afterwards 
extinguished in passing through the atmosphere is well known to artillerists. 
The general appearance (and in this appearance there is wonderful uniformity) is 
represented in Plate 15. fig. 5, and gives the idea of the combustion having proceeded 
from centres of ignition. 
If we imagine a grain, or rather (taking into account the size of the grains of 
the present day) a pebble, of powder arriving unconsumed at a point a little in advance 
of that of maximum pressure, it is not difficult to conceive that such pebble will 
traverse the rest of the bore without being entirely consumed, when the great influence 
of diminished pressure, combined with the shortness of time due to the increasing 
velocity of the projectile, is considered. 
Thus by reference to Table X. it will be found that the time taken by the projectile to 
describe the firstfoot (’305 metre) of motion is about ‘005 second, while the time taken 
to describe the remaining length of the bore, 7'25 feet (2’21 metres), is only about 
•Oil second. 
The mean powder-pressure over the first foot, again, is about 15 tons per inch 
(2300 atmospheres), and over the remainder of the bore is only 5’25 tons (800 atmo- 
spheres). 
W. TEMPEEATURE OF PRODUCTS OF COMBUSTION IN BORES OF GUNS. 
The temperature in the bore of the gun during the expansion of the products is 
given by equation (28), or, restoring the values of v' and v' 0 , 
t— 
C p-Cy 
\ V 0 {l—Ci) )c c +f3.\ 
M V-XV 0 / 
(31) 
The temperatures calculated from this formula are given in Table XIX. It is hardly 
necessary to point out that the values given in this Table are only strictly accurate 
when the charge is ignited before the projectile is sensibly moved; but in practice the 
correction due to this cause will not be great. 
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