Sugars

Sugars. Although originally the term sugar" was given to all substances which were characterised by a sweet taste, it is now confined to a number of carbohydrates (q.v.) which are all closely related in both their chemical and physical properties. They are all obtained as products of animal and vegetable life, and until recent years all attempts to prepare them synthetically had proved abortive. The earhest known was ordinary cane-sugar; afterwards the sweet products derived from beet, maple, sorghum, etc., were recognised as similar; while one by one milk-sugar, grape-sugar, and other varieties were added to the list of these compounds. Chemically they may be divided iuto two classes - the sucroses, resembling cane-sugar and possessing the formula C₆H₂₂O₁₁; and the glucoses, of which grape-sugar is a type, to which corresponds the formula C₆H₁₂O₆. They are neutra1 substances, soluable in water, and usually capable of being obtaied crystalline. Professor E. Fischer, by whom their artificlal syntheses have been effected, has shown that in their chemical nature they are compounds belonging to the class of either ketones (q.v.) or aldehydes - i.e. possessing the general formula X.CO.X or X.CHO, where X is a hydrocarbon radical. Almost all possess the power of acting on polarised light, most of them existing in three varieties, which are respectively dextrorotatory, laevorotatory, and inactive. Of the sucrose, cane-sugar is the best known. There seems evidence that the cultivation of the sugar-cane was first carried on in Eastern Asia, and crude sugar was obtained from the same source in the 7th century by the Chinese. The cultivation spread westward, and during the Middle Ages Venice was one of its most important seats, while it was further spread west by the agency of the Spanish traders. The sugar-cane (Saccharum officinarum), of which many varieties exist, is a great species of grass, the stalks of which reach usually a height of about 12 feet. When ripe, the canes are cut down close to the ground, the leaves and shoots taken off and the canes immediately crushed by steel rollers. The juices from the crushers are collected in a trough, where they form a yellowish-green, turbid liquid. This is filtered through sieves and treated with milk of lime in large iron vessels or clarifiers, until a thlck scum is formed upon the surface. The underlying clear liquid is drawn off and concentrated in copper pans until sufficiently strong, when It is set aside to crystallise, the portion which still remains liquid being known as molasses. The raw product still requires refining. For this purpose the crude sugar is dissolved in water in large iron tanks, kept well stirred, and heated by steam, after which it is strained through cotton bags, and is decolorised by passing through many layers of animal charcoal. It is then concentrated under reduced pressure in large vessels (vacuum pans), and poured into moulds to crystallise completely, the crystals being finally dried in centrifugal machines. Methods essentially similar in most respects are employed for the prodnction of sugar from beet and maple. Pure cane-sugar is a white crystaline compound, which forms crystals of the monoclinic system. It melts at 160° C., but decomposes If heated further. Under the influence of dilute acids and of certain ferments it splits up, into glucose and levulose, the process being known as inversion. This mixture may then, by the further action of the ferment, undergo some of the numerous forms of fermentation (q.v.), as that resulting in the formation of alcohol. Milk-sugar or lactose (q.v.), which crystallises in rhombic prisms, and maltose, which results from the action of diastase on starch, as in brewing, both possess the same composition as cane-sugar, and resemble it in most of their chemical properties. Of the glucoses, the best-known are grape-sugar, also known as dextrose or glucose, and fruit sugar, also known as fructose or levulose. Other varieties of this class are mannose, a derivative of mannite, which occurs in various plant seeds: galactose, obtained from lactose by the action of acids; and sorbinose, which occurs largely in mountain ash berries, [CARBOHYDRATE, FERMENTATION.]