Elongated and cylindrical grains.
If the form of the grain be elongated, then will the quantity of gas generated in a given time from a grain of similar weight to that of the cube or sphere, be increased, on account of the greater ignited surface, and consequently the time necessary for its combustion will be diminished. If it be of a cylindrical form for example, this time must be reckoned from the diameter of the cylinder, its length not influencing it in the least, although as we have seen, it enters into the consideration of the quantity of the gas generated in a given time.
Large grain.
In the ordinary large-grain powder, the majority of the grains are of the elongated or flat form, from whence considerable advantage is derived, particularly in short guns, since it causes the greatest portion of the charge to be decomposed before the projectile is moved sensibly from its original position.
Mealed powder.
If the charge be composed of mealed powder a longer time is found to be necessary for the complete combustion of the whole than in the case where the substance is granulated, and the initial velocity of a shot is reduced about one third by employing the substance in that state.
The effect of granulating gunpowder.
A piece of pressed cake weighing 1·06oz., was put into a mortar, and a globe of some light substance, placed upon it, and the powder being consumed after ignition without ejecting the ball from the bore of the piece. When an equal quantity was divided into seven or eight pieces, the globe was thrown out of the mortar; breaking the cake into twelve pieces; the ball ranged 3·3 yards; being further increased to fifty grains, it ranged 10·77 yards; and when the ordinary powder was used, the ball was projected 56·86 yards.
Action depends upon size and form of grain.
It will appear from the above remarks, that the force generated from the charge of powder in a gun, will be greatly influenced by the size and form of the grains composing it.