Yes; but it appears to me in that state very different from animal fat. MRS. B. The essential constituent parts of either vegetable or animal oils are the same, carbon and hydrogen; their variety arises from the different proportions of these substances, and from other accessory ingredients that may be mixed with them. The oil of a whale, and the oil of roses, are, in their essential constituent parts, the same; but the one is impregnated with the offensive particles of animal matter, the other with the delicate perfume of a flower. The difference of _fixed oils_, and _volatile_ or _essential oils_, consists also in the various proportions of carbon and hydrogen. Fixed oils are those which will not evaporate without being decomposed; this is the case with all common oils, which contain a greater proportion of carbon than the essential oils. The essential oils (which comprehend the whole class of essences and perfumes) are lighter; they contain more equal proportions of carbon and hydrogen, and are volatilized or evaporated without being decomposed. EMILY. When you say that one kind of oil will evaporate, and the other be decomposed, you mean, I suppose, by the application of heat? MRS. B. Not necessarily; for there are oils that will evaporate slowly at the common temperature of the atmosphere; but for a more rapid volatilization, or for their decomposition, the assistance of heat is required. CAROLINE. I shall now remember, I think, that fat and oil are really the same substances, both consisting of carbon and hydrogen; that in fixed oils the carbon preponderates, and heat produces a decomposition; while, in essential oils, the proportion of hydrogen is greater, and heat produces a volatilization only. EMILY. I suppose the reason why oil burns so well in lamps is because its two constituents are so combustible? MRS. B. Certainly; the combustion of oil is just the same as that of a candle; if tallow, it is only oil in a concrete state; if wax, or spermaceti, its chief chemical ingredients are still hydrogen and carbon. EMILY. I wonder, then, there should be so great a difference between tallow and wax? MRS. B. I must again repeat, that the same substances, in different proportions, produce results that have sometimes scarcely any resemblance to each other. But this is rather a general remark that I wish to impress upon your minds, than one which is applicable to the present case; for tallow and wax are far from being very dissimilar; the chief difference consists in the wax being a purer compound of carbon and hydrogen than the tallow, which retains more of the gross particles of animal matter. The combustion of a candle, and that of a lamp, both produce water and carbonic acid gas. Can you tell me how these are formed? EMILY.