That the effective force of gunpowder depends on the generation and expansion of sundry gaseous fluids, is evident, from the chemical action which takes place in the combustion. At a _red_ heat gunpowder explodes. This ensues even in a vacuum; a fact at once conclusive, that, while it possesses the inflammable principle, it has also the supporter of combustion. It is to be observed that the particle of powder which is struck by the spark, is instantaneously heated to the temperature of ignition, and is thereby decomposed; and the affinity existing between its oxygen or the oxygen of the nitric acid, and the charcoal and sulphur produces the principal part of the gases. The caloric thus evolved, inflames successively, though with rapidity, the remaining mass. The expansive force of powder, is therefore attributed to the sudden production of carbonic acid gas, sulphurous acid and nitrogen gas, with the water which is instantaneously converted into steam; all of which are greatly augmented by the quantity of caloric liberated. The combustion, therefore, is owing to the action of the charcoal and sulphur on the nitre; and the decomposition is the effect of the union of the charcoal with a part of the oxygen of the nitric acid, with which it forms carbonic acid, and also with the sulphur producing sulphurous acid gas. It is asserted, that sulphuretted hydrogen gas is also produced; if so, there must be a sulphuret formed, which decomposes a part of the water. After combustion, what remains is carbonate of potassa, sulphate of potassa, and a small proportion of sulphuret of potassa and unconsumed charcoal. Good powder, however, should leave no very sensible residue when inflamed: this is one of the proofs recommended. Thenard observes, (_Traité de Chimie_, ii, p. 498,) that the products of the combustion of gunpowder are numerous; some gaseous, and some solid. The gaseous products are carbonic acid, deutoxide of azote (nitrous gas) and azotic gas, besides the vapour of water; and the solid products are sub-carbonate of potassa, sulphate of potassa, and sulphuret of potassa.