GLAUBER'S SALT

glauber's salt, decahydrated sodium sulphate, na2so4, 10h2o. it is said by j. kunkel to have been known as an _arcanum_ or secret medicine to the electoral house of saxony in the middle of the 16th century, but it was first described by j. r. glauber (_de natura salium_, 1658), who prepared it by the action of oil of vitriol or sulphuric acid on common salt, and, ascribing to it many medicinal virtues, termed it _sal mirabile glauberi_. as the mineral thenardite or mirabilite, which crystallizes in the rhombic system, it occurs in many parts of the world, as in spain, the western states of north america and the russian caucasus; in the last-named region, about 25 m. e. of tiflis, there is a thick bed of the pure salt about 5 ft. below the surface, and at balalpashinsk there are lakes or ponds the waters of which are an almost pure solution. the substance is the active principle of many mineral waters, e.g. frederickshall; it occurs in sea-water and it is a constant constituent of the blood. in combination with calcium sulphate, it constitutes the mineral glauberite or brongniartite, na2so4.caso4, which assumes forms belonging to the monoclinic system and occurs in spain and austria. it has a bitter, saline, but not acrid taste. at ordinary temperatures it crystallizes from aqueous solutions in large colourless monoclinic prisms, which effloresce in dry air, and at 35 deg.c. melt in their water of crystallization. at 100 deg. they lose all their water, and on further heating fuse at 843 deg. its maximum solubility in water is at 34 deg.; above that temperature it ceases to exist in the solution as a decahydrate, but changes to the anhydrous salt, the solubility of which decreases with rise of temperature. glauber's salt readily forms supersaturated solutions, in which crystallization takes place suddenly when a crystal of the salt is thrown in; the same effect is obtained by exposure to the air or by touching the solution with a glass rod. in medicine it is employed as an aperient, and is one of the safest and most innocuous known. for children it may be mixed with common salt and the two be used with the food without the child being conscious of any difference. its simulation of the taste of common salt also renders it suitable for administration to insane patients and others who refuse to take any drug. if, however, its presence is recognized sodium phosphate may be substituted.