PHOSPHATE OF SODA.

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with benefit: as pityriasis versicolor (called also liver spots or chloasma).A solution of it in rose-water is employed as a cosmetic. In gonorrhoeaand leucorrhoea an aqueous solution has been occasionally used, as aninjection, with success. Lastly, in the form of ointment it has beenapplied to inflamed and painful hsemorrhoidal tumors.

Internally it has been used to diminish the secretion of uric acid; toact as a diuretic in dropsical cases; and to influence the uterus in thecases before mentioned. To promote uterine contractions, Dr. Coplandrecommends it in conjunction with ergot of rye.

Administration. —The dose of it is from half a drachm to a drachm.As a detergent in aphtha it may be used in powder, mixed with sugar orwith honey. The Mellite of Borax ( mel boracis, Ph . L.) consistsof a drachm of powdered borax mixed with an ounce of clarified honey;it is the most eligible form for the employment of borax in the aphtha ofchildren.

So'da Phos'phas. — Phos'phate of So’da.

History. —This salt was long known before its true nature was under-stood. In 1737 Ilellot found it in the urine. It has been known by variousnames, such as alcali minerale and sal mirabile perlatum. In the shopsit is sold as tasteless purging salts. Dr. Turner calls it triphosphate ofsoda and basic water. It is sometimes termed the rhombic phosphateof soda.

Natural History. —It has been found, in small quantities, in somemineral waters (Gairdner, On Mineral Springs, p. 19). It exists in manyanimal fluids, especially the urine of man.

Preparation. —It is procured as follows:—carbonate of soda is addedto the impure solution of phosphoric acid, obtained by digesting bone-ash in sulphuric acid ( vide p. 250) to saturation: the liquid is thenfiltered, evaporated, and put aside to crystallize. A slight excess of sodapromotes the formation of fine crystals.

Properties. —The primary form of the crystals of this salt is theoblique rhombic prism. The crystals are transparent, but by exposureto the air effloresce and become opaque. Their taste is cooling saline.They react feebly on vegetable colours like alkalies. When heated, theyundergo the watery fusion, give out water, and form a white mass whichhas been called pyrophosphate of soda: at a red heat this melts into atransparent glass, called metaphosphate of soda. The crystals of phosphateof soda require, for their solution, four times their weight of cold ortwice their weight of hot water: they are nearly insoluble in alcohol.

Characteristics. —The presence of soda in this salt is known by thetests for this base before mentioned (p. 310). The phosphoric acid in itis recognised as follows: a solution of the phosphate throws down awhite precipitate with acetate lead, as well as with chloride of barium:the precipitate in both cases is a phosphate, and dissolves in nitricacid without effervescence: with nitrate of silver, the phosphate ofsoda occasions a yellow precipitate soluble both in nitric acid andammonia: pyrophosphate of soda, obtained by heating the phosphate,produces a white precipitate with nitrate of silver: hydrosulphiuic acid,as well as the hydrosulphates, occasion no change in a solution ofphosphate of soda. Phosphate of lead fused upon charcoal, in the outerflame of the blowpipe, becomes distinctly crystalline upon cooling.