The term gravimetric density (G.D.) is peculiar to artillerists; it is required to distinguish between the specific gravity (S.G.) of the powder filling a given volume in a state of gas, and the specific gravity of the separate solid grain or cord of powder.
Thus, for instance, a lump of solid lead of given S.G., when formed into a charge of lead shot composed of equal spherules closely packed, will have a G.D. such that
| (4) | G.D. of charge of lead shot | = | 1 | π√2 = 0.7403; |
| S.G. of lump of solid lead | 6 |
while in the case of a bundle of cylindrical sticks of cordite,
| (5) | G.D. of charge of cordite | = | 1 | π√3 = 0.9067. |
| S.G. of stick of cordite | 6 |
At the standard temperature of 62° F. the volume of the gallon of 10 lb of water is 277.3 cub. in.; or otherwise, 1 cub. ft. or 1728 cub. in. of water at this temperature weighs 62.35 lb, and therefore 1 lb of water bulks 1728 ÷ 62.35 = 27.73 cub. in.
Thus if a charge of P lb of powder is placed in a chamber of volume C cub. in., the
(6) G.D.= 27.73P/C, G.V. = C/27.73 P.
Sometimes the factor 27.68 is employed, corresponding to a density of water of about 62.4 lb per cub. ft., and a temperature 12° C., or 54° F.