I have given you this summary account or enumeration of the acids, as you may find it more satisfactory to have at once an outline or a general notion of the extent of the subject; but we shall now confine ourselves to the first class, which requires our more immediate attention; and defer the few remarks which we shall have to make on the others, till we treat of the chemistry of the animal and vegetable kingdoms. The acids of simple and known radicals are all capable of being decomposed by combustible bodies, to which they yield their oxygen. If, for instance, I pour a drop of sulphuric acid on this piece of iron, it will produce a spot of rust, you know what that is? CAROLINE. Yes; it is an oxyd, formed by the oxygen of the acid combining with the iron. MRS. B. In this case you see the sulphur deposits the oxygen by which it was acidified on the metal. And again, if we pour some acid on a compound combustible substance, (we shall try it on this piece of wood,) it will combine with one or more of the constituents of that substance, and occasion a decomposition. EMILY. It has changed the colour of the wood to black. How is that? MRS. B. The oxygen deposited by the acid has burnt it; you know that wood in burning becomes black before it is reduced to ashes. Whether it derives the oxygen which burns it from the atmosphere, or from any other source, the chemical effect on the wood is the same. In the case of real combustion, wood becomes black, because it is reduced to the state of charcoal by the evaporation of its other constituents. But can you tell me the reason why wood turns black when burnt by the application of an acid? CAROLINE. First, tell me what are the ingredients of wood? MRS. B. Hydrogen and carbon are the chief constituents of wood, as of all other vegetable substances. CAROLINE. Well, then, I suppose that the oxygen of the acid combines with the hydrogen of the wood, to form water; and that the carbon of the wood, remaining alone, appears of its usual black colour. MRS. B. Very well indeed, my dear; that is certainly the most plausible explanation. EMILY. Would not this be a good method of making charcoal? MRS. B. It would be an extremely expensive, and, I believe, very imperfect method; for the action of the acid on the wood, and the heat produced by it, are far from sufficient to deprive the wood of all its evaporable parts. CAROLINE. What is the reason that vinegar, lemon, and the acid of fruits, do not produce this effect on wood? MRS. B.