Crystallization is employed to obtain crystallizable substances in a state of purity; or to separate them from each other, by taking advantage of their dif ferent solubility at different tempera tures.
General .3naksis resulting from. the cation of Chemical Powers.
The simple elementary substances into which bodies are capable of being re duced, submitted to chemical action, are light, caloric, electricity, galvanism, mag netism, oxygen, hydrogen, nitrogen, carbon, sulphur, soda, potash, phospho rus, metals, - and earths. Of these the first five have no appreciable gravity, which is evinced by all the rest. Of the latter, again, some are combustible, others incombustible; some oxygenizable, others destitute of all affinity for oxygen. But to enter minutely into these subjects would be to carry us beyond the limits of this article, and to infringe upon those that belong to chemistry as a general science, and to which, as also to the seve ral articles above enumerated in the alphabetical order, we refer the reader for further information. So little pro gress, however, have we hitherto made in the general science of chemistry, that perhaps we are even now committing a double error, in offering the above as a table of simple elementary substances. It is possible that not one of these sub stances is, strictly speaking, a simple element, or, in other words, totally un compounded of rudiments that are more simple. We may also be in an error in
conceiving every one of them to be a distinct substance from every other: we have many reasons, for example, for sup posing that galvanism and electricity are the very same substance, only in different states of modification; and some philoso phers have ventured to suspect that magnetism, or the magnetic power, is, in like manner, in unity with both. Nei ther s6da nor potash, again, are scarcely any longer to be regarded as simple substances; we have many valuable ex periments of Mr. Davy before us, by which they appear to have been coin pletely decomposed; and there can be little doubt of the full confirmation of these experiments by subsequent trials of other chemists. And in this case it is possible that metallic substances will have to be as completely struck out of the list of simple elements as potash or soda. There are also several of the acids which are still admitted into the same catalogue, but whose pretensions are every day becoming still more doubtful, and of which, on this very account, we have taken no notice, though we shall have occasion to advert to them, and especially the muriatic acid, as we pro ceed. See LIGHT, CALORIC, ELE CTRICI T Y, &C.