GLAUBER'S SALT, first described by J. R. Glauber, occurs native as the mineral mirabilite in Spain, the western States of North America, and the Caucasus. Sodium sulphate is the active principle of many mineral waters, e.g., Friedrichshall, Carlsbad waters. It occurs in sea water and is a normal constit uent of the blood. (See ALKALI MANUFACTURE.) Glauber's salt is decahydrated sodium sulphate, (see HYDRATE) ; it separates from cold aqueous solutions of sodium sulphate in colourless monoclinic prisms which effloresce in dry air and at 32.38° C melt in their water of crystallization. Its maximum solubility in water is at 32.38° C, and above that tem perature it no longer exists as decahydrate but changes to anhy drous salt, which becomes decreasingly soluble as the temperature rises. Glauber's salt readily forms supersaturated solutions in which crystallization is induced by adding a particle of the salt. In medicine it is employed as an aperient, being one of the safest and most innocuous. For children or patients who refuse other drugs it may be mixed with common salt.