Page:Popular Science Monthly Volume 12.djvu/486

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seeds, and imparting a slight astringency to the juice, retained after fermentation. In the red wines from 0.08 to 0.2 per cent, of tannin is found. The decomposition of tannin, by a fermentation producing sugar, has been mentioned under the head of sugars. Tannin is also liable to oxidation with various products not including sugar.

The vegetable kingdom furnishes numerous compounds, known as glucosides, which are capable of definite and distinctive fermentations, one of the fermentation products in each instance being sugar. A number of these glucosides are found in fruits. One of the most important of these is amygdalin, a glucoside found in the fruits, leaves, etc., of plants of the almond family, especially in the kernels of the bitter-almond, peach, and cherry, the leaves of the cherry-laurel, and the bark of the wild-cherry.

Amygdalin, when obtained pure, is a white, odorless solid, with a taste both sweet and bitter. Taken alone it is not poisonous, even in considerable quantities. But if mixed with a substance named emulsin, and wetted, amygdalin begins at once to break up, with formation of three other compounds, as follows:

Amygdalin, 457 parts (by contact with emulsin and coöperation with water) produces: 1. Bitter-almond oil, 106 parts.
2. Hydrocyanic acid (or "prussic acid"), 27 parts.
3. Glucose, 360 parts.

In the plant, amygdalin is accompanied with the emulsin needful for its fermentation. During the ripening of the fruit, and in the maturity of the leaves and other parts, the amygdalin is constantly, though slowly, being transformed into the three products above named. The bitter-almond oil and hydrocyanic acid are volatile and odorous, and give the pleasant odor of peach-kernels, almonds, etc., familiar to every one. The rapidity of the chemical change is chiefly governed by the proportion of moisture, being greatly accelerated by wetting the bruised kernels or leaves, and stopped altogether by drying, while the moisture of the living plant permits only a gradual rate of the transformation. One of the products of this change is poisonous, the well-known hydrocyanic acid, or prussic acid, one-tenth of a grain of which is a full medicinal dose. The bitter-almond oil (known to chemists as benzoic aldehyde, and easily oxidized to benzoic acid) is not in the least poisonous (when separated from the hydrocyanic acid). It will be seen from the numbers of parts resulting from the change (as given above) that one part of hydrocyanic acid and four of bitter-almond oil are produced by sixteen parts of pure amygdalin. The amygdalin of the shops, in Europe, where it is somewhat used to generate hydrocyanic acid in medicine, yields from 120 to 125 of its weight of hydrocyanic acid. In exposure to the air, the hydrocyanic acid, being very volatile, is quickly dissipated, while the bitter-almond oil vaporizes more slowly. In most fruits of the