Again, in a composition of mealed powder, rosin and sulphur, with or without the addition of saw dust, we infer, from the composition of the ingredients and the chemical action which subsequently takes place, that the products of combustion would be carbonic acid gas, sulphurous acid gas, water, sulphuretted hydrogen, and probably azotic, and nitric oxide gases. If the filings of steel, brass, zinc, or copper, enter into the composition, besides the products above-mentioned, there would be either an oxide of iron, an oxide of zinc, or, an oxide of copper, according as one or other of these metals are employed. Copper, in fire-works, has the effect of communicating a green colour to the flame. M. Homberg, (_Collection Acad._) observes, that the green colour in such cases is owing to the _dissolution_ of the metal, which in fact is nothing more than the _effect_ of its oxidizement. The various compositions for brilliant fire, as the Chinese fire, owe their peculiar character to pulverised cast iron, and commonly to steel and iron filings. Now the effects in these cases are the same; for the same oxidizement ensues, more or less rapidly, which in fact distinguishes the kinds of brilliant fire. That of the Chinese is the most perfect, and next is the composition made with steel filings. It will be seen, however, that compositions generally are governed, in their respective appearances when inflamed, by the purity, as well as the proportion of other substances, which enter into them; and hence much of their effect depends on collateral circumstances, which we purpose to consider when we treat of the compositions individually. That the light of certain burning bodies may be increased, is evident from these facts; and experiment has shown, that the intensity of the light of burning sulphur, hydrogen, carbonic oxide, &c. is increased by throwing into them, zinc, or its oxide, iron, and other metals, or by placing in them very fine amianthus or metallic gauze. Protochloride of copper burns with a dense red light, tinged with green and blue towards the edges. If the hydrogen of the oil acts in separating the chlorine from the copper, and the reduced copper is ignited by the charcoal, this appearance must necessarily ensue. When solid matter is the product of combustion, as in the burning of phosphorus, zinc, iron, &c. the flame is remarked to be more intense. Flame may be modified under other circumstances, as we will have occasion to mention hereafter. When, for instance, a wire-gauze safety-lamp is made to burn in a very explosive mixture of coal gas and air, the light is very feeble and of a pale colour; but when a current of coal gas is burnt in atmospheric air, the combustion is rapid and the flame brilliant.