TARTRATE OF POTASII.

451

Fig. 71.

in the boiling waler, thcn add tlie bitartrate of potash, and boil. Strain the liquor, and after-wards boil it down until a pellicle fioats, and set it aside that crystals raay be formed. Theliquor being poured off, dry these, and again evaporate the liquor that crystals may be pro-duced.

The processes of the Edinburgh and Dublin Colleges are essentially the same. [And alsothat of the U. S. Pharmacopoeia.]

In this prooess the excess of acid in the bitartrate is saturated by the potash ofthe carbonate; the carbonic acid escapes.

Properties. —In is usually met with in the shops in a granulär State, but itought to be crystallized. Its crystals are right rhombicprisms. To the taste this Salt is saline, and somewhatbitler. It deliquesces when exposed to the air, and issoluble in its own weight of waler at 50°; the Solutiondecomposes by keeping.

Characleristics. —When heated to redness it is de-composed, leaving as a residue charcoal and carbonateof potash. A Solution of the tartrate produces whiteprecipitates with Solutions of acetates of lead, nitrate ofsilver, and chloride of calcium; the precipitates beingsoluble in nitric acid. Bichloride of platinum, assistedby heat, causes a black precipitate in a Solution of thissalt. When heated, the Salt evolves the odour of cara-mel. If an excess of any strong acid (as the sulphuric) be added to a Solution ofthis salt, we obtain crystals of the bitartrate. Heiice acids, and most aciduloussalts, are incompatible with it: as also are tamarinds. The tartrate is readily dis-tinguished from the bitartrate by its deliquescent property, its greater solubility,and its want of acidity.

Comfositton. —The following is the composition of this salt:—

Crystulof Tartrate ofPotash.

Atoms.

Et/. Wt.

..... « ...

..... 66 ...

Per Cent...... 57-9 ...

Berielius., 4l:il___ 58-69

Tartrate of Potash. 1 ........ 114 ........ 100-0 ........ 100 00

The large crystals contain, according to Dr. Thomson, (Firsl Prlnciples ofChemistry, vol. ii. p. 264.) two equivalents of water. The same authority states,that he has had crystals of this salt in needles which seemed to contain no waterofcry stali zation.

Impurity.— It may contain excess of acid or of base, either of which is easilyrecognised ; the one by litmus, the other by turmeric. The sulphates may bedetected by chloride'of barium throwing down a white precipitate insoluble in nitricacid.

Physiological Effects. —This salt is a gentle purgative, analogous in its actionto the sulphate of potash, from which it differs in being milder in its Operation, andpartially digestible; for, like the other vegetable salts of the alkalis, it is decomposedin the System, and converted into the carbonate, in which State it is found in theurine.

It is said to have the power of preventing the griping of other more activecathartics, as senna and scammony ; but, from my own personal observations, Idoubt the correctness of this Statement.

Uses. —It is employed as a mild purgative in dyspepsia, at the commencementof diarrhosa, in some liver complaints, &c. Sometimes it is used as an adjunct toother more active purgatives; as the infusion of senna.

Administration. —it may be given in doses of from two or three drachms tohalf an ounce, or even an ounce.

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