SUGAR (Lat. and Gr. sacehar-, Sans. saykara, Pers. schakar, Arab. sokkar or assokkar, Sp. azucar, It. zucchero, Fr. sucre, Ger. sucker) is a general term applied by chemists to a number of neutral carbohydrates, possessing a more or less sweet taste, for the • most part crystallizable, and produced by the vital processes going on in certain plants and animals. They are divisible into two groups, the first embracing such sugars as are capable of undergoing fermentation, and of being resolved, under the action of yeast, either directly or indirectly into alcohol and carbonic acid gas; and the second including those sugars which are not capable of being broken up by fermentation into the above named products. The first group contains cane-sugar or sucrose, fructose or inverted sugar, trehalose, mycose, melezitose, melitose, grape-sugar or glucose (q.v.), and milk sugar or lactose. while the second group includes inosite or inosin, sorbite or sorbin, and scyllite or scyllin.
Caine-sugar or sucrose the ordinary sugar of commerce, is by far the moat important of this class of compounds; and in so far as its sweetening properties are con cerned, it exceeds grape-sugar in the ratio of 5 to 2, and milk-sugar in a still higher ratio. It has a specific gravity of 1.6. It dissolves in about one-third of its own weight of cold water, producing a thick viscid syrup, and in all proportions in hot water; it is slightly soluble in absolute alcohol, but spirit of wine of specific gravity 0.830 dissolves about one-fourth of its weight. By the spontaneous evaporation of its watery solution it is deposited in four-sided rhomboidal prisms. Common loaf-sugar and sugar-candy are two well-known forms of crystallized sugar; the former consisting of a mass of . small transparent crystals, and owing its dazzling whiteness to the numerous reflec tions and refractions which the rays of light undergo within the interior from the num berless crystals of which it is composed; while the brown color which the latter usually possesses is due to the coloring matter not having been removed from the syrup previous' to crystallization. The crystals of sugar-candy are larger than those of loaf-sugar, in consequence of the slower evaporation in the former case. When crystals of sugar— as, for example, two pieces of loaf-sugar—are rubbed together in the dark, a pale phos phorescent light is evolved. If a solution of sugar be boiled for a long time it acquires an acid reaction and loses its power of crystallizing—a change which is attended by the assimilation of additional water, and the formation of the uncrystallizable inverted sugar which will be presently described. If the boiling be further prolonged the inverted
sugar assimilates more water, and is converted into grape-sugar (C12His 2Aq), while a little formic acid and ulmin (a brown, nearly insoluble substance belonging to the humus group) are produced. The crystallization of sugar is also pre vented by the addition of a little oxalic, citric, malic, or any of the stronger acids to its solution; and in order to check the bad effects of an acid, a small quantity of lime is usually added to the cane-juice before it is heated.
The action of different degrees of heat on sugar has been carefully studied. At about 320° sucrose fuses, and on cooling forms the transparent amber-colored solid known as barley-sugar, which, if kept for a long time, assumes a crystalline state, and becomes opaque. If the application of heat be continued until about 400°, the sugar loses two atoms of water, and caramel, which is described in the article GLUCOSE, is formed, and at a still higher temperature, the changes which sucrose undergoes are identical with those suffered by glucose. Sugar dissolves many metallic oxides when its solution is boiled with them—as, for example, freshly precipitated oxide of lead, lime, and baryta, and its presence prevents the precipitation of alkalies of various metallic oxides from their salts—the oxides of copper and of iron being thus retained in solution, Many metallic oxides are partially or entirely reduced when boiled with sugar; thus chromic acid is reduced to sesquioxide of chromium, salts of the red oxide of mercury are con verted into those of the suboxide, and salts of -gold give a precipitate of the reduced metal. It does not reduce alkaline solutions of oxide of copper to the suboxide (Trom mer's test) unless with the aid of heat, which converts it into glucose. Under the action of certain oxidizing agents it may be converted into propionic, formic, and acetic acids. Sucrose is not directly capable of undergoing fermentation; but in the presence of a ferment (yeast, for example) it is converted into glucose, and in that form it readily undergoes vinous, lactic, and butyric fermentation. Its action on polarized light is described below.