Saccharum Lactis, B.P. Milk Sugar.
C12H22O11, H2O = 360.192.
Milk sugar, C12H22O11, H2O is a crystalline sugar obtained from the whey of milk by gently evaporating to a low bulk, and setting aside for a day or two, when the sugar crystallises out as a yellow, granular mass, and is subsequently purified by treatment with animal charcoal, and repeated crystallisation. Milk sugar is also official in the U.S.P. It occurs in hard, gritty, odourless, crystalline masses, or as a white or greyish-white, non-hygroscopic powder, having a faintly sweet taste. Its aqueous solution is neutral to litmus, and is dextrorotatory. When heated to 130° it loses its water of crystallisation without melting, and leaves a white hygroscopic mass. Dilute acids convert it into galactose and dextrose. It becomes brown on hearing with alkalies, and reduces Fehling's solution. Its aqueous solution acidified with hydrochloric acid should not respond to any of the tests for the heavy metals; nor when boiled in water and the solution cooled should it give any reaction for starch with iodine. The occasional presence of magnesium or calcium salts in commercial milk sugar is apparently due to the addition of magnesia or lime to the whey during the process of crystallisation, in order to neutralise the acid used to curdle the milk. The presence of those salts is objectionable, because they induce or assist coagulation of milk to which the sugar may be added in preparing food for infants. More than traces, of lactic acid must also be avoided for the same reason.
Soluble in water (1 in 6), boiling water (1 in 1), insoluble in alcohol, ether, or chloroform.
Action and Uses.—Milk sugar is a valuable nutrient, especially when there is extreme irritability of the stomach. It is less sweet than cane sugar and is less liable to ferment. It is largely employed in the humanisation of cow's milk for the use of young infants. Undiluted fresh cow's milk contains about 4.5 percent. of milk sugar, whilst normal human milk approximates to 6.5 percent. When cow's milk is diluted with water to reduce the casein content, milk sugar is added to bring up the strength to 6.5 per cent. of the whole. Milk sugar is slightly laxative and diuretic. It has been used in full doses (8 to 16 grammes daily) as a diuretic in renal dropsy. It is employed in pharmacy as a diluent of powerful drugs to subdivide the medicament . It is an excellent diluent for grey powder and calomel, and is preferable to powdered cane sugar for this purpose. It is used as an absorbent in the preparation of some extracts, but though less prone to absorb moisture than cane sugar, it is not so suitable for this purpose as an inert vegetable powder.