Nitre, or saltpetre, is strictly the essence of gunpowder. It is a triple compound of oxygen, nitrogen, and potassium. The chemical action of those elements on each other, and the play of affinities between them at a high temperature, occasion the immense effect produced by gunpowder on the application of fire or heat. By universal consent, sulphur is included in the mixture, but it is not absolutely necessary for the “propellant power;” for nitre and charcoal only will generate effects similar to the compound with sulphur. Gunpowder made without sulphur has, however, several bad qualities; it is not, on the whole, so powerful, nor so regular in its action; it is also porous and friable, possessing neither firmness nor solidity. It cannot bear the friction of carriage, and in transport crumbles into dust. The use of sulphur, therefore, appears to be not only to complete the mechanical combination of the other ingredients, but being a perfectly combustible substance, it increases the general effect, augments the propellant power, and is thought to render the powder less susceptible of injury from atmospheric influence. “There is one good reason,” says the Edinburgh Encyclopædia, “for the use of sulphur, although it does not contribute to the production of any elastic fluid. The carbonic acid which is generated would doubtless combine with the potash, if it were not for the presence of the sulphur, and thus so much elastic fluid would be lost. That this is the case we know to be true, from the fact that carbonate of potash is always formed when nitre is decomposed by charcoal alone, which I shall almost immediately show.” This certainly would be the case, to a certain extent, with gunpowder without sulphur--some carbonate of potash would be formed. The sulphur, we have no doubt, from experiments we have made on this subject, is, in part, engaged during the explosion of gunpowder in expelling the sixth proportion of oxygen from the potash, so as to combine with the potassium, to form a true sulphuret of that metal. This fact is easily ascertained, from the circumstance that no sulphuretted hydrogen can be detected, by the most delicate tests, coming from the residuum left after firing gunpowder, until moisture has gained access to it. The bad smell which arises sometime after the burning of gunpowder, is occasioned by the decomposition of the moisture which the sulphuret of potassium attracts from the atmosphere; giving rise, by this decomposition and liberation, to the fœtid foul gas, called sulphuretted hydrogen, and the production of potassa, or the oxide of potassium. A commission of French chemists and artillerists was appointed by the Government, in the year 1794, to experiment upon the best proportions and constituents of gunpowder for the use of the French service. The following were the proportions of five different kinds prepared at the Essonne works:--