If the substance in any state such as B were allowed to expand **adiabatically** (dH = o) down to the absolute zero, at which point it contains no heat and exerts no pressure, the whole of its available heat energy might theoretically be recovered in the form of external work, represented on the diagram by the whole area BAZcb under the adiabatic through the state-point B, bounded by the isometric Bb and the zero isopiestic bV.

In., and that the gas expands **adiabatically** up to the muzzle, where B_216 +25.8_3.75 b 2.5X25.8 we find the work realized by expansion is 2826 foot-tons, sufficient to increase the velocity from 1020 to 2250 f/s at the muzzle.