When three parts of nitre, two parts of potash, and one of sulphur, all previously well dried, are mixed together, the compound is called _pulvis fulminans_, or, _fulminating powder_. A small portion of this powder, or as much as will lay on a shilling-piece, put on a shovel, and exposed to heat, will first melt, become liver-coloured, and then explode with great noise. The theory of this explosion is, that a part of the sulphur, and the potassa unite, and form a sulphuret; the sulphuret then decomposes water, and produces sulphuretted hydrogen gas, which appears to be decomposed by the nitric acid; and there results sulphurous acid gas, water, and, as Thenard observes, protoxide of azote, azotic gas, and sulphate of potassa. The loudness of the report depends on the combustion of the whole powder at the same instant, which is secured by the previous fusion it undergoes. Gunpowder, on the contrary, burns in succession, although apparently instantaneous. In using common potash, there is also, as the alkali contains it, carbonic acid, given out in the state of gas. In fact carbonic acid appears to assist the explosive effect of this powder, for when it is prepared with potash, containing little carbonic acid, its detonating power is considerably less. Nitre likewise enters into the composition of another fulminating powder, invented by Dr. Higgins. _Higgins's fulminating powder_ is composed of three and a half parts of nitre, two parts of crude antimony, and one part of sulphur. This is used in the same manner as the former. Nitre enters into the composition of gunpowder, which we shall notice under a separate head. The proportions of nitre, sulphur, and charcoal, for the formation of gunpowder, which are considered the best, are, 75 parts of nitre, 12-1/2 of charcoal, and 12-1/2 of sulphur. The new powder of MM. Gengembrie and Bottée, which inflames by percussion, but without explosion, is composed of 21 parts of nitre, 54 parts of chlorate of potassa, 18 parts of sulphur, and 7 parts of lycopodium. A mixture of nitre and crude antimony projected into a red-hot crucible, produces a deflagration more or less rapid, forming a composition which is used in pharmacy, and medicine. The quality of saltpetre may be determined by a variety of experiments. Fire-workers judge of its quality by the colour of its flame. The flame should be white. If it be _green_ or _yellow_, it is said to be impure.