With metric units, measuring P in kg., and C in litres, the G.D. = P/C, G.V. = C/P, no factor being required.
From the Table I., or by quadrature of the curve in fig. 9, the work E in foot-tons realized by the expansion of 1 lb of the powder from one gravimetric volume to another is inferred; for if the average pressure is p tons per sq. in., while the gravimetric volume changes from v - ½Δv to v + ½Δv, a change of volume of 27.73Δv cub. in., the work done is 27.73pΔv inch-tons, or
(7) ΔE = 2.31 pΔv foot-tons;
and the differences ΔE being calculated from the observed values of p, a summation, as in the ballistic tables, would give E in a tabular form, and conversely from a table of E in terms of v, we can infer the value of p.
On drawing off a little of the gas from the explosion vessel it was found that a gramme of cordite-gas at 0° C. and standard atmospheric pressure occupied 700 ccs., while the same gas compressed into 5 ccs. at the temperature of explosion had a pressure of 16 tons per sq. in., or 16 × 2240 / 14.7 = 2440 atmospheres, of 14.7 lb per sq. in.; one ton per sq. in. being in round numbers 150 atmospheres.
The absolute centigrade temperature T is thence inferred from the gas equation
(8) R = pv / T = p0v0/273,
which, with p = 2440, v = 5, p0 = 1, v0 = 700, makes T = 4758, a temperature of 4485° C. or 8105° F.
In the heading of the 6-in. range table we find the description of the charge.