Let me reflect . . . . Both the candle and lamp burn by means of fixed oil--this is decomposed as the combustion goes on; and the constituent parts of the oil being thus separated, the carbon unites to a portion of oxygen from the atmosphere to form carbonic acid gas, whilst the hydrogen combines with another portion of oxygen, and forms with it water. --The products, therefore, of the combustion of oils are water and carbonic acid gas. CAROLINE. But we see neither water nor carbonic acid produced by the combustion of a candle. MRS. B. The carbonic acid gas, you know, is invisible, and the water being in a state of vapour, is so likewise. Emily is perfectly correct in her explanation, and I am very much pleased with it. All the vegetable acids consist of various proportions of carbon and hydrogen, acidified by oxygen. Gums, sugar, and starch, are likewise composed of these ingredients; but, as the oxygen which they contain is not sufficient to convert them into acids, they are classed with the oxyds, and called vegetable oxyds. CAROLINE. I am very much delighted with all these new ideas; but, at the same time, I cannot help being apprehensive that I may forget many of them. MRS. B. I would advise you to take notes, or, what would answer better still, to write down, after every lesson, as much of it as you can recollect. And, in order to give you a little assistance, I shall lend you the heads or index, which I occasionally consult for the sake of preserving some method and arrangement in these conversations. Unless you follow some such plan, you cannot expect to retain nearly all that you learn, how great soever be the impression it may make on you at first. EMILY. I will certainly follow your advice. --Hitherto I have found that I recollected pretty well what you have taught us; but the history of carbon is a more extensive subject than any of the simple bodies we have yet examined. MRS. B. I have little more to say on carbon at present; but hereafter you will see that it performs a considerable part in most chemical operations. CAROLINE. That is, I suppose, owing to its entering into the composition of so great a variety of substances? MRS. B. Certainly; it is the basis, you have seen, of all vegetable matter; and you will find that it is very essential to the process of animalization. But in the mineral kingdom also, particularly in its form of carbonic acid, we shall often discover it combined with a great variety of substances. In chemical operations, carbon is particularly useful, from its very great attraction for oxygen, as it will absorb this substance from many oxygenated or burnt bodies, and thus deoxygenate, or _unburn_ them, and restore them to their original combustible state. CAROLINE.