203. _GLAUBER SALT, or SULPHAT of SODA, is a salt which consists of soda (200) in combination with sulphuric acid (24). It occurs in an efflorescent or powdery state, on the borders of salt lakes; or, more commonly, in a state of solution, in certain mineral waters._ This salt, which was originally discovered by a German chemist whose name was Glauber, has a nauseously bitter and saline taste. It is found, in an efflorescent state, on meadow ground at Eger, in Bohemia; and on the walls of old galleries in mines, at Grenoble, in France. It is also abundant in the ashes of some kinds of vegetables, especially of sea weeds. The waters of the Mediterranean yield a great proportion of it; and the Glauber salt used for commercial purposes is chiefly prepared from sea─water, or by decomposing common salt, in order to procure muriatic acid (29). It may also be obtained by saturating soda with sulphuric acid (24). The use of this salt in medicine is well known; and, in some countries, it is employed as a substitute for soda (200), in the manufacture of white glass. It ought to be kept in well─corked bottles, as otherwise the crystals soon fall into powder. The following is a pleasing experiment, which shows a singular and almost instantaneous crystallization of Glauber’s salt. Dissolve this salt by adding portions of it gradually to water kept boiling until the water will dissolve no more. Pour the solution, whilst boiling, into common medicine phials previously warmed, and immediately cork them. Set the phials in a quiet place without shaking them. The solution, when cool, will remain perfectly fluid till the cork is taken out; but the moment this is done, and the air is admitted, it will begin to crystallize on its upper surface, in fine satin─like crystals, which will shoot downward, like a dense white cloud. In this act so much heat becomes evolved as to make the phial feel sensibly warm to the hand. When the crystallization is complete, the whole mass generally becomes so solid, that, on inverting the bottle, not a drop of it will fall out. If the crystallization should not immediately ensue on opening the phial, this may instantly be effected by dropping into it a minute crystal of the same salt. The experiment may be exhibited any number of times afterwards, by merely placing the phial in boiling water, till the salt it contains be again completely liquefied; and letting it stand, as before, to cool. 204. _BORAX is a salt composed of boracic acid (28) and soda (200), and is imported chiefly from the East Indies, in the form of a brownish grey, impure, shapeless salt, of sweetish taste; or in detached prismatic crystals, each about an inch in length._