The common temperature of the atmosphere in the cellars in which the juice of the grape is fermented is sufficiently warm for this purpose; and as the juice contains an ample supply of water, there is no occasion for any addition of it. But when fermentation is produced in dry malt, a quantity of water must necessarily be added. EMILY. But what are precisely the changes that happen during the vinous fermentation? MRS. B. The sugar is decomposed, and its constituents are recombined into two new substances; the one a peculiar liquid substance, called _alcohol_ or _spirit of wine_, which remains in the fluid; the other, carbonic acid gas, which escapes during the fermentation. Wine, therefore, as I before observed, in a general point of view, may be considered as a liquid of which alcohol constitutes the essential part. And the varieties of strength and flavour of the different kinds of wine are to be attributed to the different qualities of the fruits from which they are obtained, independently of the sugar. CAROLINE. I am astonished to hear that so powerful a liquid as spirit of wine should be obtained from so mild a substance as sugar. MRS. B. Can you tell me in what the principal difference consists between alcohol and sugar? CAROLINE. Let me reflect . . . . . Sugar consists of carbon, hydrogen, and oxygen. If carbonic acid be subtracted from it, during the formation of alcohol, the latter will contain less carbon and oxygen than sugar does; therefore hydrogen must be the prevailing principle of alcohol. MRS. B. It is exactly so. And this very large proportion of hydrogen accounts for the lightness and combustible property of alcohol, and of spirits in general, all of which consist of alcohol variously modified. EMILY. And can sugar be recomposed from the combination of alcohol and carbonic acid? MRS. B. Chemists have never been able to succeed in effecting this; but from analogy, I should suppose such a recomposition possible. Let us now observe more particularly the phenomena that take place during the vinous fermentation. At the commencement of this process, heat is evolved, and the liquor swells considerably from the formation of the carbonic acid, which is disengaged in such prodigious quantities as would be fatal to any person who should unawares inspire it; an accident which has sometimes happened. If the fermentation be stopped by putting the liquor into barrels, before the whole of the carbonic acid is evolved, the wine is brisk, like Champagne, from the carbonic acid imprisoned in it, and it tastes sweet, like cyder, from the sugar not being completely decomposed. EMILY. But I do not understand why heat should be evolved during this operation. For, as there is a considerable formation of gas, in which a proportionable quantity of heat must become insensible, I should have imagined that cold, rather than heat, would have been produced. MRS. B.