Syn. Cream of Tartar. Crystals of Tartar. Supertartrate of Potassa. Acid Tartrate of Potassa.

Preparation

The juice of the grape contains a considerable proportion of bitartrate of potassa. When undergoing the vinous fermentation, it gradually deposits this salt, because the alcohol produced renders the water of the juice less capable of holding it in solution. A crust is thus formed upon the inner surface of the cask, which, on being removed, constitutes crude tartar, or argol. This is sometimes white, and sometimes reddish, according to the character of the wine. The bitartrate of potassa, which is the chief ingredient, though mixed with numerous impurities, is obtained from it by repeated solution in water and crystallization. The crystals deposited are called the crystals of tartar. in the process of evaporation, when the solution has become saturated, and is allowed to cool, a layer of very minute crystals forms on the surface of the water, which, when separated, are designated as the cream of tartar. But the latter name has been extended so as to apply to the salt in a state of powder, however prepared, and, indeed, to the medicine in all conditions, without reference to its state of aggregation. The crystals are imported from France, and pulverized after reaching this country. in the retail shops, the salt is always kept in the form of powder.

Properties

As imported, bitartrate of potassa is in the state of small irregular lumps or masses, consisting of small crystals aggregated together, which are whitish, translucent, permanent in the air, hard, and, when chewed, gritty under the teeth. The powder is beautifully white, soft, inodorous, of a sour, not disagreeable taste, of difficult solubility in water, requiring 180 parts of cold, and 18 of boiling water for solution, and insoluble in alcohol. The addition of borax or boracic acid renders it much more soluble in water. The watery solution undergoes spontaneous decomposition on exposure. At a red heat, the salt is decomposed, being converted into vapours, which escape, and a mixture of charcoal with carbonate of potassa, which remains.

Composition and Chemical Reactions. Bitartrate of potassa contains two equivalents of tartaric acid, one of potassa, and one of water; and the water cannot be separated without destroying the salt. By means of other alkaline bases, or their carbonates, the excess of tartaric acid is saturated and double salts formed. Potassa or its carbonate converts it into the neutral tartrate. The bitartrate effervesces with alkaline carbonates, and, in solution, affords precipitates with lime-water and the soluble salts of lime or calcium, baryta or barium, and lead.

Medical Properties and Uses

Cream of tartar has the properties of the saline cathartics generally. While less energetic as a purgative than sulphate of magnesia, it is probably even more hydragogue, certainly more refrigerant, and more apt to be absorbed and act upon the kidneys. it is somewhat disposed to produce flatulence and griping, probably in consequence of the decomposition of a portion of the tartaric acid. When long continued, it is thought to weaken digestion, give rise to various dyspeptic symptoms, and produce emaciation. But these effects have, I think, been exaggerated, for I have often given it for weeks and months together; and though, like all other cathartics, it will sometimes occasion uneasiness and other unpleasant symptoms, yet I know none which can be borne better upon the whole, unless it may be rhubarb and the mildest laxatives. in great excess, it may possibly, as has been stated, inflame the bowels. The case of a drunkard is on record, who, to obviate the effects of drinking, took four or five tablespoonfuls of the powder, and was soon afterwards attacked with vomiting, purging, and other symptoms of gastro-intestinal inflammation, of which he died. (Tyson, Lond. Med. Gaz., xxi. 17?.) But I have, in many dropsical cases, administered two ounces daily of cream of tartar, for weeks, in divided doses, and never yet saw any effects which were at all dangerous in their character; and cannot help suspecting, that the previous debauch of this patient had more to do with the result than the cream of tartar.

This cathartic is admirably adapted to the treatment of dropsy; but, as it is more efficient in that complaint when used to increase the urine, than with a view to its purgative effects, it will be most appropriately considered with the diuretics, in reference to this application.

When used as a cathartic in dropsy, cream of tartar is most frequently combined with jalap. (See Jalapa, vol. II. p. 541.)

Associated with sulphur, it is much used in painful and inflamed hemorrhoids. Equal parts of the two may be mixed, and two drachms of the mixture given for a dose.

Added to senna tea, in the proportion of one or two drachms to the pint, it is thought to lessen the tendency of that cathartic to gripe.

It is not unfrequently employed in solution, as a laxative and refrigerant drink, in febrile complaints. For this purpose, from a drachm to a drachm and a half may be dissolved in a pint of boiling water, and flavoured with sugar and lemon-peel, or oil of lemons. This drink, which is called imperial, is not very different in taste from lemonade, and may be taken at pleasure.

The dose of bitartrate of potassa is one or two drachms as a laxative, and from half an ounce to an ounce as a cathartic. in small quantities, it may be taken in the form of an electuary with molasses or syrup; but, on the whole, the best method of administration is to suspend it by agitation with water, or some mild aromatic infusion, to prevent griping, as fennel-seed tea.

Bitartrate of potassa enters into the composition of the Confectio Sulphuris, Br. (see page 410); and of the Pulvis Jalapae Compositus, U. S., Br. (see page 541).