138 



Capt. Noble and Mr. F. A. Abel. 



[May 29, 



suffered five expansions during the motion of the projectile in the gun, 

 the gravimetric density of the charge being unity, the table shows that 

 for every pound or kilogramme in the charge an energy of 91*4 foot- 

 tons, or 62,400 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 realised in the projectile. 



But it rarely happens, especially with the very large charges nsed in 

 the most recent guns, that gravimetric densities so high as unity are 

 employed ; 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 snppose 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 62,400 kilogrammetres, above 

 given, there must be subtracted 19*23 foot-tons, or 13,127*3 kilogram- 

 metres, 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. 



The authors then discuss the causes which in the bore of a gun 

 affect the energy realised by gunpowder, and point out that this energy 

 varies very much with the powders employed, being in this respect 

 dependent upon circumstances, such as the density of the powder, its 

 size of grain, the amount of moisture, chemical composition, nature of 

 charcoal used, &c, &c, but that the energy may also vary considerably 

 even with the same powder, if the charges be not fired under precisely 

 the same circumstances. For example, especially with slow burning 

 powders, the weight of the shot fired exerts a very material influence 

 upon the factor of effect;, and the reason is obvious : the slower the 

 shot moves at first, the earlier in its passage up the bore is the charge 

 entirely consumed, and the higher is the energy realised. The same 

 effect, unless modified by other circumstances, is produced when the 

 charge is increased with the same weight of projectile. In this case 

 the projectile has to traverse a greater length of bore before the same 

 relief due to expansion is attained. The higher pressures which con- 

 sequently rule react upon the rate of combustion of the powder, and 

 again a somewhat higher energy is obtained. 



Both these increased effects, of course, correspond to an increased 

 initial tension of Jie powder- gases, but, especially with the smaller 

 guns, a very great difference in the realised energy may arise from 

 other causes. 



