You have, I believe, a clear idea of the nomenclature by which the base (or radical) of the acid, and the various degrees of acidification, are expressed? EMILY. Yes, I think so; the acid is distinguished by the name of its base, and its degree of oxydation, that is, the quantity of oxygen it contains, by the termination of that name in _ous_ or _ic_; thus sulphure_ous_ acid is that formed by the smallest proportion of oxygen combined with sulphur; sulphur_ic_ acid that which results from the combination of sulphur with the greatest quantity of oxygen. MRS. B. A still greater latitude may, in many cases, be allowed to the proportions of oxygen than can be combined with acidifiable radicals; for several of these radicals are susceptible of uniting with a quantity of oxygen so small as to be insufficient to give them the properties of acids; in these cases, therefore, they are converted into oxyds. Such is sulphur, which by exposure to the atmosphere with a degree of heat inadequate to produce inflammation, absorbs a small proportion of oxygen, which colours it red or brown. This, therefore, is the first degree of oxygenation of sulphur; the 2d converts it into sulphur_ous_ acid; the 3d into the sulphur_ic_ acid; and 4thly, if it was found capable of combining with a still larger proportion of oxygen, it would then be termed _super-oxygenated sulphuric acid_. EMILY. Are these various degrees of oxygenation common to all the acids? MRS. B. No; they vary much in this respect: some are susceptible of only one degree of oxygenation; others, of two, or three; there are but very few that will admit of more. CAROLINE. The modern nomenclature must be of immense advantage in pointing out so easily the nature of the acids, and their various degrees of oxygenation. MRS. B. Till lately many of the acids had not been decomposed; but analogy afforded so strong a proof of their compound nature, that I never could reconcile myself to classing them with the simple bodies, though this division has been adopted by several chemical writers. At present there are only the muriatic and the fluoric acids, which have not had their bases distinctly separated. CAROLINE. We have heard of a great variety of acids; pray how many are there in all? MRS. B. I believe there are reckoned at present thirty-four, and their number is constantly increasing, as the science improves; but the most important, and those to which we shall almost entirely confine our attention, are but few. I shall, however, give you a general view of the whole; and then we shall more particularly examine those that are the most essential. This class of bodies was formerly divided into mineral, vegetable, and animal acids, according to the substances from which they were commonly obtained. CAROLINE. That, I should think, must have been an excellent arrangement; why was it altered? MRS. B.