Density of gunpowder.
In order to obtain a gunpowder which shall possess a proper amount of force, it is necessary that the ingredients should be thoroughly incorporated, and the process of incorporation will in great measure affect the density of the grains. After going through the process, it is subjected to a certain pressure, in order that the substance in travelling may not be reduced to a fine powder, which would cause the velocity of transmission of inflammation to be diminished. But there is a certain point beyond which it would not be advantageous to increase the density, and this seems to vary with the size of the grain. With large-grain powder the action in a musket, or in guns with small charges, is greatest with a low density; while with very small grain, the highest velocities are obtained generally with the gunpowder of great density; but in heavy guns with ordinary charges, the large-grained powder should be of considerable density in order to obtain the greatest effect, though still it must not be too great.
Advantages of glazing.
The principal advantages of glazing are; first, that the powder so prepared, will in travelling, owing to the smaller amount of destructive force consequent on friction, produce less mealed powder; and secondly, that in a damp country like England, the glazing imparts a preserving power to the powder, as the polished surface is less likely to imbibe moisture than the rough.
Disadvantages of glazing.
The disadvantages of glazing consists in its polishing the surface, and thus depriving it of those angular projections which cause the ignition and combustion to be carried on with greater rapidity, by rendering the interstices smaller, the consequence of which is, that there is not so much gas produced previously to the projectile leaving the gun, and in large charges a portion will be blown out unfired. There must be a limit then to glazing, which it would not be proper to exceed. Experiments as to glazing.At an experiment with glazed and unglazed powder, the ranges on the eprouvette were 75 for glazed, and 98 for unglazed. This loss of power, consequent on glazing, has caused it to be done away with in France and Russia. Glazing less hurtful to fine grains.With fine grain powder it is not of so much consequence, as it is, to a certain degree, corrected by the size of the grain.
Size of grain determined by size of charge.
The rapidity with which a charge of gunpowder is consumed will depend not only in a certain degree upon the size of the grain, but on the manner in which the charge is put together, for if a charge is closely pressed, the gases meeting resistance in their endeavours to escape between the interstices, will not propagate the ignition so rapidly. With large charges, there exists a positive advantage for the grains to be rather large, so that the most distant parts of the charge should be reached by the gases as quickly as possible; whilst with that of a rifle, the charge being small, the fineness of the grain does not interfere with the quantity of the gas developed. Whence it may rationally be concluded that the dimensions of the grains should increase in proportion to the quantity of the charges into which they are to enter, that is to say, in proportion to the interstices. Tight ramming bad.Ramming down a charge tightly must therefore interfere with the velocity of combustion.
Note—The foregoing on the explosive force of gunpowder was taken from Lieut-Colonel E. M. Boxer’s Treatise on Artillery.