Page:Popular Science Monthly Volume 7.djvu/736

716 cannot live without the aid of the oxygen of the air. Furthermore, they fix this oxygen upon the alcohol contained in the wine according to the following equation: 46 parts, by weight, of alcohol unite with 32 parts of oxygen to form 60 parts of acetic acid and 18 parts of water. The combustion which results from the taking up of these 32 parts of oxygen is such that the whole surface of the liquid to a certain depth shows a temperature several degrees higher than that of the deeper portions; clouds of vapor rise above the cask, clouds formed mainly of steam, mingled with a few odorous products and some vapor of acetic acid. Little by little all these external phenomena diminish and finally cease entirely, and the mycodermic pellicle falls inert to join the preceding ferment at the bottom of the reservoir. And now instead of a reservoir of wine we have a reservoir of vinegar, in which our learned colleague may again see, at his leisure, and still sentimentally, a result of divine foresight, in the form of a final cause.

But let us continue. Our task—that is, the determination of the return of the organic matter to the atmosphere and to the soil—has been very little furthered by the second phase of the phenomena which we have just described; the alcohol, 100 parts of which contain more than 52 parts of carbon, more than 13 parts of hydrogen, and nearly 35 parts of oxygen, all coming from the original sugar, has indeed disappeared and given place to the acetic acid, but the matter has not become gaseous, it has not returned to the atmosphere as it partly did at the beginning. All the carbon of the alcohol has remained in the newly-formed acetic acid.

Notice what now takes place in our immense reservoir of vinegar, at the bottom of which lie heaped together the stems, the pellicle, the pits, the cells, the parenchyma of the fruit, and our two ferments, the wine-yeast and the vinegar-yeast. The quiet of which I spoke, and which was established a moment ago, has not lasted long: the ferment of the vinegar (and the fact is very curious) which has just fallen to the bottom of the cask, exhausted by the immense chemical work which it has produced, rendered inert by the sharp combustion of which it has been the seat, reappears, little by little, on the surface of our acid liquid, always in the form of a very thin pellicle; and, little by little, again the upper strata of the vinegar heat, and again clouds rise above the liquid. These clouds are no longer composed solely of the vapor of water; the latter is still very abundant in them, but it is mingled with torrents of carbonic-acid gas, and this remarkable phenomenon continues as long as any acetic acid remains in the liquid; in other words, after the vinegar ferment, an aërobic ferment—one needing air—has burned the alcohol and turned it into water and acetic acid, it burns the latter and turns it into water and carbonic acid. It also burns the original acids of the grape.

This time, that is, in the third phase of the phenomena, the return to the atmosphere has gone on rapidly: all the carbon, all the