Characters. - In transparent, oblique prisms. It has a salt and bitter taste and effloresces on exposure to the air.

Solubility. - It is soluble in water, insoluble in spirit.

Reactions. - It gives the reactions of sodium (p. 617) and of a sulphate (p. 595).

Preparation, B.P. - May be obtained from the residue left in the manufacture of hydrochloric acid, by neutralising it with carbonate of sodium, and crystallising from solution in water.

Dose. - 1/4 to 1 ounce.

Uses. - Sulphate of sodium, when introduced into the stomach, is supposed to excite peristaltic movements in it, and to have a similar action upon the intestine. It produces in the intestine a secretion of watery fluid, and acts as a purgative. It is used either alone, or mixed with bicarbonate of sodium, in ulcer of the stomach, chronic gastritis, and dilatation of the stomach. A mixture of sulphate and bicarbonate of sodium has been used in imitation of the Carlsbad salts obtained by evaporation of the natural mineral water of Carlsbad. The mixture, or the natural salts, ought to be taken dissolved in warm water immediately after rising, and it is better to sip the solution at intervals, while dressing, than to drink the whole off at a draught (p. 406). One-third of a teaspoonful of the crystallised salts in a large tumblerful of warm water, taken immediately on rising, is frequently sufficient to produce one free action of the bowels after breakfast, and no more. This quantity of salts, with a smaller quantity of water, may have no action; and if a smaller quantity of water be used along with a larger quantity of salts it not unfrequently happens that several scanty motions occur during the day, with considerable discomfort in the abdomen.

Carlsbad water, natural or artificial, is also useful in bilious disorders, and in persons of a gouty diathesis. A gentle course will often remove the dulness, irritability, and other symptoms which accompany biliary derangements or precede a gouty attack. It may be used, also, with advantage in chronic constipation and tendency to congestion of the brain or of the abdominal and pelvic organs. A continued course of the water is exceedingly beneficial in cases of excessive obesity, and also in diabetes mellitus.

The Carlsbad waters contain a number of other salts which are not crystallised out, and they often prove much more efficient when drunk at the springs than when the solution of the salts is taken by patients at their own homes. The great benefit which is often obtained from a course of the waters at Carlsbad is no doubt due in great measure to the diet and regimen which patients will follow there in company with others, but which nothing would induce them to conform to while at home.