Page:Popular Science Monthly Volume 21.djvu/519

Rh again, and the angle through which it has been moved is read on a divided circle and vernier.

Since the rotation is less for the sodium-ray than for the transition tint, the two are distinguished by different symbols. For the former the symbol [a]D is used, and for the latter [a] or [a]j. The one-color saccharimeter is especially to be recommended for those who may be subject to any degree of color-blindness. A discussion of the optical principles involved in circular polarization would be out of place here.

Fermentation is a peculiar decomposition which sugars suffer under the influence of a nitrogeneous germ called the "ferment."

Cane-sugar, under the influence of a mucous sporule, undergoes "mucous fermentation," and is converted into a gum and a kind of sugar called "mannite." Neither acid nor alcohol is produced by this process.

Lactic fermentation takes place under the influence of an organism called penicilium glaucum. The chief product of this fermentative is lactic acid. In the case of a dextrose it may be represented by the following equation:

Milk-sugar undergoes this fermentation most readily, first absorbing a molecule of water and then breaking up into four molecules of lactic acid. If the process is allowed to go on, the lactic acid will break up into butyric acid, carbonic dioxide, and hydrogen. If the Torula aceti take the place of the germ named above, cane-sugar especially will yield acetic instead of lactic acid.

The vinous is by far the most important of the fermentations to which sugars are subjected.

Ordinary yeast is the nitrogenous body which seems best suited to develop this change.

Cane-sugar, before undergoing vinous fermentation, absorbs a molecule of water and is changed by an active principle of the yeast into invert-sugar. The chief products of vinous fermentation are alcohol and carbonic dioxide. Less important products are succinic acid, glycerine, cellulose, and fat.

All the sugar, with the exception of about four per cent., is converted into the two products first named. By an equation, the process may be represented as follows:

The peculiar fungus which is most active in the vinous fermentation is saccharomyces cerevisiæ; but there is much about the process which is yet obscure.

In the conversion of starch into sugar by diastase or acids, and the conversion of sugar into alcohol by fermentation, we have the rationale of that vast industry carried on by distillers and brewers. If the