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Sugar is a crystalline substance, differing from starch by its sweet taste and solubility in cold water. As food, its uses are the same as starch; all starch must be converted into sugar before it can be assimilated.

The principal kinds of sugar are: cane sugar or sucrose, grape sugar or glucose (C₆H₁₂O₆), milk sugar or lactose (C₁₂H₂₂O₁₁), and fruit sugar or levulose (C₆H₁₂O₆).

Cane sugar is obtained from sugar cane, beets, and the palm and sugar-maple trees. Sugar cane is a grass supposed to be native to Southern Asia, but now grown throughout the tropics, a large amount coming from Cuba and Louisiana; it is the commonest of all, and in all cases the manufacture is essentially the same. The products of manufacture are: molasses, syrup, brown sugar, loaf, cut, granulated, powdered, and confectioners’ sugar. Brown sugar is cheapest, but is not so pure or sweet as white grades; powdered and confectioners’ sugars are fine grades, pulverized, and, although seeming less sweet to the taste, are equally pure. Confectioners’ sugar when applied to the tongue will dissolve at once; powdered sugar is a little granular.

Cane sugar when added to fruits, and allowed to cook for some time, changes to grape sugar, losing one-third of its sweetness; therefore the reason for adding it when fruit is nearly cooked. Cane sugar is of great preservative value, hence its use in preserving fruits and milk; also, for the preparation of syrups.

Three changes take place in the cooking of sugar: first, barley sugar; second, caramel; third, carbon.

Grape sugar is found in honey and all sweet fruits. It appears on the outside of dried fruits, such as raisins, dates, etc., and is only two-thirds as sweet as cane sugar. As a manufactured product it is obtained from the starch of corn.

Milk sugar is obtained from the milk of mammalia, but unlike cane sugar does not ferment.

Fruit sugar is obtained from sweet fruits, and is sold as diabetin, is sweeter than cane sugar, and is principally used by diabetic patients.