Some Physico–Chemical Properties of Lactose: VI. The Solubility of Lactose in Salt Solutions; The Isolation of a Compound of Lactose and Calcium Chloride

Abstract

Summary Lactose is more soluble in molar solutions of calcium chloride or of calcium nitrate than in pure water. Increase in the concentration of salt brings further increase in the solubility of lactose. This phenomenon is believed to be related to the anomalous rotations of lactose in salt solutions. The increased solubility of lactose in calcium chloride solutions is due to the formation of a molecular compound of alpha lactose and calcium chloride in solution. A study of the solubility of lactose in calcium chloride solutions indicated the existence of only one compound at 25°C. This compound was isolated. It has the composition alpha lactose ·CaCl 2 ·7H 2 O. Hydrated lactose is exceedingly soluble in concentrated solutions of calcium chloride, (or calcium bromide), but these solutions are supersaturated with respect to the compound just mentioned. Such solutions are often exceedingly stable, and may resist all attempts to induce crystallization. Faith in the reliability of polariscopic data as evidence of the formation of lactose compounds in salt solutions has been strengthened by the fact that lactose, in the solutions tested, exhibited an increased solubility, and furthermore, by the fact that one such compound has been isolated. Such data indicate that many salts may combine with lactose. The existence of such molecular compounds is possibly a factor contributing to the stability of such supersaturated solutions of lactose as are found in ice cream and in milk powders.