134 
CAPTAIN NOBLE AND ME. F. A. ABEL ON FIEED GUNPOWDER, 
performing during the given expansion is then taken out from the Table ; and this work 
being multiplied by the number of kilogrammes or pounds in the charge gives the total 
maximum work. Thus, for example, in an 18-ton 10-inch gun, a charge of 70 lb. 
(31-75 kilos.) pebble powder is fired, and we wish to know what is the maximum work 
that the charge is capable of performing. We readily find that the length of the gun 
is such that ^ = 5*867 vols. ; and from the Table we find that 89-4 foot-tons or 61,000 kilo- 
grammetres is the maximum work per lb. or per kilog. ; multiplying by the number of 
pounds or kilos., we find that 6258 foot-tons or 1,936,750 kilogrammetres is the maxi- 
mum work which the whole charge is capable of performing. 
As a matter of course, this maximum effect is only approximated to, not attained ; 
and for actual use it would be necessary to multiply the work so calculated by a factor 
dependent upon the nature of the powder, the mode of firing it, the weight of the shot, 
■&c. ; but in service-powders fired under the same circumstances the factor will not 
vary much. In the experimental powders used by the Committee on Explosives there 
were, it is true, very considerable differences, the work realized in the same gun varying 
from 56 foot-tons to 86 foot-tons per lb. of powder ; but with service-powders fired 
under like conditions this great difference does not exist. 
We have prepared at once, in illustration of the principles we have just laid down, 
as a test of the general correctness of our views and as likely to prove of considerable 
utility, a Table in which we have calculated, from the data given, first, the total 
work realized per lb. of powder burned for every gun, charge, and description of 
powder in the English service ; second, the maximum theoretic work per lb. of powder 
it would be possible to realize with each gun and charge ; and third, the factor of effect 
with each gun and charge — that is, the percentage of the maximum effect actually 
realized. 
If the factors of effect be examined, it will be observed how, in spite of the use of 
slow-burning and therefore uneconomical powders in the large guns, the percentages 
realized gradually increase as we pass from the smallest to the largest gun in our Table 
— the highest factor being 93 per cent, in the case of the 38-ton gun, the lowest being 
50‘5 per cent, in the case of the little Abyssinian gun. 
This difference in effect is of course in great measure due to the communication of 
heat to the bore of the gun, to which we have so frequently referred. 
Y. DETERMINATION OF TOTAL THEORETIC WORK OF POWDER WHEN INDEFINITELY 
EXPANDED. 
To determine the total work which powder is capable of performing if allowed to 
expand indefinitely, the integral in equation (33) must be taken between co and v 0 . If 
circumstances discussed at p. Ill, the total work, as shown in the text, which the charge is capable of effecting, 
is 6258 foot-tons; multiplying this by the factor for the gunpowder and weight of shot, we have W=4880 
foot-tons; substituting this value of W in the above equation, we obtain i;=1532 feet, or nearly identical with 
the observed velocity. — February 1875. 
