This section is from the book "Cassell's Cyclopaedia Of Mechanics", by Paul N. Hasluck. Also available from Amazon: Cassell's Cyclopaedia Of Mechanics.
The proportions for the ingredients of gunpowder employed at the end of the nineteenth century are given in the following table: -
Gunpowder is an intimate mechanical mixture, not a chemical compound, chemical action taking place when it is ignited. The gaseous products formed by ignition are carbonic acid gas, carbonic oxide, and nitrogen. The explosive force depends upon the amount of gas generated, the heat to which it is raised, and the rapidity with which it is formed. Charcoal supplies the body to be burned, nitrate of potassium the oxygen to support combustion, and sulphur raises the temperature of the gases, and thus increases their expansive force, which, for heavy rifled guns and large charges, is as much as 25 tons to the square inch. All the powder used in the English service is of the same composition, and varies for different purposes only in the size and density of the grains to vary the rate of explosion. By this means, without lessening the velocity given to the projectile, the strain on the gun can be reduced. The larger the gun the greater the density and size of the grains. Thus for 80- and 100-ton guns, prismatic powder of hexagonal shape, from lin. to 1 1/3 in. thick, and having a density of 1.75, is used, whereas for rifles and machine guns fine grain is employed, having a density of 1.72.