This gas, therefore, in conjunction with other gases, formed at the same time, all of which being expanded, causes what is denominated the _explosive effect_ of gunpowder. We have then a primary cause of the decomposition, and most of the effective force of gunpowder is owing to the carbonic acid; and it is found, that gunpowder made without sulphur is equally powerful as that with, since it adds nothing to its power. Causes, therefore, chemically speaking, operate alike under similar circumstances. The materials made use of being equally pure, and used in the same proportion, the effect must necessarily be the same. It is not only in the instance we have mentioned, but in every other, in which chemical action ensues, that this doctrine is tenable. We might, indeed, notice a number of cases of a similar kind; as, for instance, in the combustion of many incendiary preparations, as fire-stone, fire-rain, composition for carcasses, light-balls, and a variety of fire-works of the same kind. If we mix pitch, tar, tallow, &c. with nitrate of potassa, and burn the mixture, we have the combined action of two elementary substances, which enter into the composition of these bodies, namely, carbon and hydrogen. The products would be carbonic acid gas, and water; because the oxygen of the nitre would unite with the hydrogen, as well as the carbon. If we employ sulphur at the same time, another product would be sulphurous acid gas, and probably sulphuric acid; and if gunpowder be used, as in the _fire-stone_ composition, then, besides these products, we would have those of the gunpowder. As this subject, however interesting to the theoretical pyrotechnist, cannot be understood without a knowledge of chemistry, it is obvious, that that science is a powerful aid to pyrotechny. It is unnecessary to dwell on this head. We may add, nevertheless that, in order to understand the effect of all mixtures, or compositions made use of, it is necessary to consider the nature of the substances employed, and the manner in which chemical action takes place, and consequently the products, which determine in fact the characteristic property of each species of fire-work, and the phenomena on which it is predicated. All products of combustion depend on the substances thus decomposed, and by knowing the effects, we may readily refer them to their proper causes.