240 CAPTAIN - NOBLE AND MR. F. A. ABEL ON FIRED GUNPOWDER. 
the projectile in the gun, the gravimetric density of the charge being unity, the table 
shows us that for every pound or kilogramme in the charge, an energy of 91'4 foot- 
tons or 62,394 kilogrammetres will as a maximum be generated. 
If the factor of effect for the powder be known, the above values multiplied by that 
factor will give the energy per pound or kilogramme that may be expected to be 
raised in the projectile. 
But it rarely happens, especially with the very large charges used in the most 
recent guns, that gravimetric densities so high as unity are employed, and in such 
cases, from the total realisable energy must be deducted the energy which the powder 
would have generated had it expanded from a density of unity to that actually 
occupied by the charge. 
Thus in the instance above given, if we suppose the charge instead of a gravimetric 
density of unity to have a gravimetric density of ’8, which corresponds to a volume of 
expansion of 1*25, we see from Table XI. that from the 91'4 foot-tons or 62,394 
kilogrammetres above given there must be subtracted'" 19"23 foot-tons, or 13,127‘3 
kilogrammetres, leaving 72*17 foot-tons or 49,272 - 8 kilogrammetres as the maximum 
energy realisable under the given conditions per pound or per kilogramme of the charge. 
As before, these values must be multiplied by the factor of effect to obtain the 
energy realisable in the projectile. 
But to apply these principles to an actual case. The factor of effect of a certain 
brand of pebble powder having been found in a powder-proof gun to be with that gun 
between '82 and '84, let us examine what are the energies likely to be realised with 
charges of 70'90 and 100 lb. in an 8-inch gun, of 130 and 140 lb. in a 10-inch gun, 
and of 235 lb. in an 11-inch gun. 
We have selected these instances both because the same powder was used in the 
experiments, and because they offer considerable variety with respect to the number of 
expansions and the gravimetric densities of the charges. 
Taking first the 8-inch gun. The number of expansions that the charges expe¬ 
rienced in the bore of the gun and the original gravimetric densities of the charges 
were as follow :— 
For a charge of 70 lb., number of expansions 6'12, gravimetric density '605 
„ 90 „ „ „ 476 „ „ '780 
„ „ 100 „ „ „ 4'29 „ „ '865 
Hence from Table XI. the maximum energy realisable is 
For the 70 lb. charge, 99'4 foot-tons —37'60 foot-tons =61 '80 foot-tons per lb. 
„ 90 „ „ 89'3 „ -20'86 „ =68'44 
„ 100 „ „ 84'9 „ -13'66 „ =71*24 
* This correction, as has been elsewhere pointed out by one of us, is only approximate. 
