It is sometimes as much beyond our power to obtain a simple body in a state of perfect purity, as it is to imitate a complicated combination; for the operations by which nature separates bodies are frequently as inimitable as those which she uses for their combination. This is the case with carbon; all the efforts of chemists to separate it entirely from other substances have been fruitless, and in the purest state in which it can be obtained by art, it still retains a portion of hydrogen, and probably of some other foreign ingredients. We are ignorant of the means which nature employs to crystallize it. It may probably be the work of ages, to purify, arrange, and unite the particles of carbon in the form of diamond. Here is some charcoal in the purest state we can procure it: you see that it is a very black, brittle, light, porous substance, entirely destitute of either taste or smell. Heat, without air, produces no alteration in it, as it is not volatile; but, on the contrary, it invariably remains at the bottom of the vessel after all the other parts of the vegetable are evaporated. EMILY. Yet carbon is, no doubt, combustible, since you say that charcoal would absorb oxygen if air were admitted during its preparation? CAROLINE. Unquestionably. Besides, you know, Emily, how much it is used in cooking. But pray what is the reason that charcoal burns without smoke, whilst a wood fire smokes so much? MRS. B. Because, in the conversion of wood into charcoal, the volatile particles of the former have been evaporated. CAROLINE. Yet I have frequently seen charcoal burn with flame; therefore it must, in that case, contain some hydrogen. MRS. B. Very true; but you must recollect that charcoal, especially that which is used for common purposes, is not perfectly pure. It generally retains some remains of the various other component parts of vegetables, and hydrogen particularly, which accounts for the flame in question. CAROLINE. But what becomes of the carbon itself during its combustion? MRS. B. It gradually combines with the oxygen of the atmosphere, in the same way as sulphur and phosphorus, and, like those substances, it is converted into a peculiar acid, which flies off in a gaseous form. There is this difference, however, that the acid is not, in this instance, as in the two cases just mentioned, a mere condensable vapour, but a permanent elastic fluid, which always remains in the state of gas, under any pressure and at any temperature. The nature of this acid was first ascertained by Dr. Black, of Edinburgh; and, before the introduction of the new nomenclature, it was called _fixed air_. It is now distinguished by the more appropriate name of _carbonic acid gas_. EMILY. Carbon, then, can be volatilized by burning, though, by heat alone, no such effect is produced? MRS. B.