Gunpowder consists of a very intricate mixture of sulphur, carbon (charcoal), and nitrate of potash (nitre).
The proportions in which they exist are one equivalent of nitre, one of sulphur, and three of carbon. The great explosive power of gunpowder is due to the sudden development from its solid constituents of a large quantity of gases; these gases are nitrogen and carbonic acid.
At the ordinary temperature of the atmosphere these gases would occupy a space three hundred times greater than the bulk of the gunpowder used; but owing to the intense heat developed at the moment of explosion, the gases occupy at least 1,500 times the bulk of the original gunpowder. The mixture, consisting of one equivalent of nitre, one of sulphur, and three of carbon, would yield three equivalents of carbonic acid, one of nitrogen, and one of sulphuret of potassium. The change may be represented thus,—
S + C₃ + KONO₅ = 3 CO₂ + N + KS.
The only solid residue, therefore, is the sulphuret of potassium, and this is the compound which produces the sulphurous odour on washing out a gun barrel; water is decomposed, sulphuretted hydrogen and potash being the result of the decomposition.
Now supposing the elements of gunpowder to exist in these proportions, it is essential, in order to secure their perfect combination, and thus to produce the largest possible volume of gas, that the elements should be in the most minute state of subdivision. Chemical action is a force exerted at insensible distances only, and chemical substances having the greatest affinity for each other will not combine, unless their elements are brought into immediate contact: thus oxygen and hydrogen may be mixed together in the exact proportions to form water; but no chemical combination will occur, simply because the ultimate particles of the two gases are not sufficiently near to each other for their chemical affinities to be brought into play; if, however, these gases are subjected to very strong pressure, so as to bring their particles into immediate contact, combination occurs, and the production of water is the result.
In order to insure the perfect combination of the elements of gunpowder the same conditions are necessary; that is to say, the ultimate particles of the nitre, charcoal, and sulphur, must be brought into the most direct contact, or the explosive power of the gunpowder will be comparatively trifling. If, for instance, the nitre, charcoal, and sulphur be pounded in a mortar, no explosion but a slow combustion will occur when the mixture is ignited; so that unless this intimate mixture of the elements is carefully attended to in the manufacture of gunpowder, it is easy to see that the article produced will be of comparatively little value.
It is evident then that if tons of the elements of gunpowder were stored in a warehouse which accidentally caught fire, no explosion would occur from the formation of gunpowder; though its ingredients would greatly increase the rapidity of combustion.
This remark is elicited by the recollection of a fearful explosion which took place at Gateshead in 1854.