SUGAR. Referring to Suomi in the NATURAL HISTORY Drvisioet of this Cyclopedia for an account of its distribution in the organic kingdom, and to a separate article [SUGAR CULTURE AND MANUFAC TURE] for information concerning the extraction from the sugar-cane, and purification of common or cane-sugar, we shall at present only con sider sugar from a chemical point of view.
Sugar—in Persian,shakkur, and origina.lysarkara (Sanscrit)—may be defined as a body having a sweet taste, and which, under the influence, direct or indirect, of ferments, splits up into alcohol and carbonic acid. As few plants are wholly destitute of sugar, and as many contain it in considerable proportions, it is not surprising that many so-called varieties of sugar should have been described from time to time. Thus we read of sugar of starch, sugar of raisins, sugar of milk, sugar of gelatine, cane-sugar, grape-sugar, manna-sugar, &c. &c. Many of these, however, have been shown to be identical, and at present nearly all may be included under four varieties, namely : Sucrose, or cane-sugar, including sugar from the beet-root, turnip, carrot, maple, birch, palm, Indian corn, and many fruits of tropical plants; Glucose, including grape sugar, and the sugar generally found in dried fruits; Fructose, the state in which sugar exists in recently plucked fruits; and Lactose, the sweet principle found in the milk of animals.
Berthelot divides the whole class of sugars, properly so called, into two fundamental groups, of which sucrose and glucose are the respec tive types. The glucose group is characterised by fermenting directly in contact with yeast ; by being destroyed by strong alkalies, even in the cold, and readily at 212° Fahr. ; by the reducing action on putts sio-tartrate of copper ; and by the circumstance that when dried in a water-bath the members of this group are isomeric, having the formula The members of the glucose group differ from each other in their crystalline form ; in their rotatory power on polarised light [SACCHARIMETRY]; in the modifications they undergo when exposed to the influence of heat or acids ; in the nature of their combinations with water, bases, and chloride of sodium ; and in the manner of their conversion into mucic acid, &c. Under the sucrose group,
Berthelot includes all sweet principles analogous to cane-sugar ; they with difficulty ferment under the influence of yeast ; are scarcely changed by alkalies, or by potassio-tartrate of copper, even at a tem perature of 212° Fahr.; are, by the action of acids, readily converted into new sugars belonging to the glucose group; and are isomeric only when heated to 266° Fahr., having then the composition The members of the sucrose group are distinguished from each other by their crystalline form ; rotatory power ; unequal resistance to heat, acids, and ferments; in their behaviour to bodies with which they combine ; and in the formation of mucic acid, &c. Sugar of milk (lactose), however, stands in a position intermediate between the above groups; resembling the glucose series in the action of alkalies and copper-salts upon it, it is nevertheless analogous to sucrose in resisting the action of heat and ferments, and capability of being converted into a fermcntible sugar.
The four chief varieties of sugar differ slightly from each other in composition, and very widely in appearance and sweetening power. Sucrose has the formula or possibly double that its appearance and taste are well known. Glucose, or grape-sugar (C„H„0„4- 2Aq.) has considerably less than half the sweetening power of cane-sugar, and is generally met with as a somewhat soft and granular, rather than crystalline mass. Fructose (chic/as/me) (C„H„.0,0 is also less sweet than sucrose, and is, moreover, unerystal fixable. And finally, lactose occurs in hard, gritty, main millated crystalline masses, and is considerably inferior in sweetness to any of the ether sugars.