FORMULA: C12H22O11+H2O. MOLECULAR WEIGHT: 359.16.
SYNONYMS: Milk-sugar, Lactin, Lactose.
"A peculiar, crystalline sugar, obtained from the whey of cow's milk by evaporation, and purified by recrystallization"—(U. S. P.).
Preparation and Description.—Remove from milk its fat and casein by precipitation with rennet. The residual thin fluid is called "whey;" this, evaporated to the consistence of molasses, clarified by white of eggs, strained and evaporated, forms sugar of milk crystals on cooling. To purify them, redissolve in boiling water, decolorize by animal charcoal, and recrystallize, repeating the process as often as may be necessary. Or, the whey is decolorized by running it through animal charcoal and concentrated in vacuum pans. Neutralization of the free acid is stated to increase the yield of milk-sugar. It is met with in commerce in powder form, or in crystallized cylindrical pieces of various lengths, and from 2 to 4 inches in diameter. Until about 1890, most of the milk-sugar in the American market came from Switzerland; since then, sugar of milk is being manufactured in America on a large scale and is competing even in the European markets (see Amer. Jour. Pharm., 1897, p. 161, 1892, p. 386, and 1893, p. 158). As described by the U. S. P., it is "in white, hard, crystalline masses, yielding a white powder feeling gritty on the tongue, odorless, and having a faintly sweet taste. Permanent in the air. Soluble in about 6 parts of water at 15° C. (59° F.), and in 1 part of boiling water; insoluble in alcohol, ether, or chloroform. The aqueous solution of sugar of milk is neutral to litmus paper"—(U. S. P.). Milk-sugar loses its water of crystallization, without melting, when heated to 130° C. (266° F.), leaving a white hygroscopic mass. A higher heat causes it to become yellow. At 170° C. (338° F.) or above it is converted into lacto-caramel (C6H10O5).
Milk-sugar, by boiling with diluted acids, is converted into galactose (C6H12O6) and dextrose (C6H12O6), hence, like cane-sugar, belongs to the compound group called saccharobioses. Milk-sugar as such is probably not capable of undergoing vinous fermentation; it ferments, however, after conversion by acids, e.g., lactic acid which is formed in the presence of lactic ferments. Alcohol and mannit are additional products of milk-sugar fermentation. Sugar of milk reduces Fehling's solution more slowly than grape-sugar. "On adding to a few Cc. of a hot, saturated aqueous solution of sugar of milk an equal volume of sodium hydrate T.S., and gently warming, the liquid will turn yellow and brownish red. On the further addition of a few drops of copper sulphate T.S., a brick-red precipitate will appear"—(U. S. P.).
To test milk-sugar for cane-sugar, the U. S. P. directs the following test: "If about 1 Gm. of powdered sugar of milk be sprinkled upon about 5 Cc. of cold sulphuric acid contained in a flat-bottomed capsule, the acid may acquire a greenish or reddish but no brown or brownish-black color within half an hour (absence of cane-sugar)"—(U. S. P.).
Action, Medical Uses, and Dosage.—The principal medicinal use of sugar of milk is in the trituration of drugs; to aid in rendering them finer and more energetic, as well as to assist in more easily dividing active agents which are to be given in minute doses; thus, if we wish to divide 1 grain of strychnine into 20 doses, it may be thoroughly triturated with 19 grains of sugar of milk, and 1 grain of the mixture gives the required dose. Or, 1 grain of resin of podophyllum, which, in general, is a cathartic dose, by long trituration with 10 grains of sugar of milk, will form several purgative doses. In these cases, the trituration should always continue for from 1 hour to 1 ½ hours. As a medicinal agent, sugar of milk is thought to be practically inert, yet Germain Sée and others declare it a powerful hydragogue diuretic, and have employed it in doses of 1 to 6 ounces well diluted with water, or milk, and in a concentrated syrup in dropsies of cardiac origin. Though being a non-nitrogenous substance, it has been employed as an article of diet in pulmonary and other affections where such diet is desirable; also, as a nutrient in excessive gastric irritability. On account of its lesser liability to fermentation in the stomach it is preferable to cane-sugar for sweetening infant foods.