Syn. Rochelle Salt. Salt of Seignette. Tartarized Soda.

Preparation and Composition. The salt is prepared by saturating the excess of tartaric acid of bitartrate of potassa by means of carbonate of soda; the former salt being gradually added, in powder, to a boiling hot solution of the latter, until carbonic acid ceases to escape, and saturation is effected. The solution is then concentrated and crystallized. A salt is thus obtained, consisting of one equivalent of tartrate of potassa and one of tartrate of soda, with eight or ten equivalents of water; the proportion of the water being differently stated by different authorities.

Properties

Rochelle salt is in fine, large, colourless, prismatic crystals, which, when perfect, have eight or ten unequal sides, but often appear as if split longitudinally into two portions. These crystals are inodorous, of a saline, slightly bitterish taste, less disagreeable than that of most other purgative salts, soluble in four parts of cold and much less of boiling water, and insoluble in alcohol. They are slightly efflorescent, and, when heated, first melt, and then give out their water of crystallization. At a high temperature they are decomposed, and, if the ignition is conducted in close vessels, a mixture of charcoal and the carbonates of potassa and soda is left.

Incompatibles. Tartrate of potassa and soda is decomposed by most acids and acidulous salts, which abstract the soda, and reconvert the salt into bitartrate of potassa. it is also incompatible with the soluble salts of lime or calcium, and lead, with the bases of which its tartaric acid forms insoluble tartrates.

Medical Properties and Uses

This salt has been in use since the year 1672, when it was first prepared by Seignette, an apothecary of Rochelle, in France, whence it derived two of the names by which it is commonly known. it has all the properties of the saline cathartics generally, but is milder than the sulphates of magnesia and soda, and of a less disagreeable taste, and probably sits somewhat better on the stomach. in small doses, of about a drachm every two or three hours, it seldom purges much; but is absorbed, and, its acid being decomposed, renders the urine alkaline.

It is much employed as an aperient in delicate persons, when a gentle refrigerant effect is indicated, together with evacuation of the bowels. Within a short period, it has been considerably employed in the treatment of inflammatory rheumatism, with the view of rendering the blood more alkaline. I have imitated the practice in several cases. The salt is given in the dose of a drachm every two or three hours. in the course of three or four days, the urine, if at first acid, generally begins to undergo change, gradually passing to an alkaline condition; and not unfrequently an amelioration of the symptoms takes place. But I have not met with success equal to that obtained by some others; and do not feel confident, from what I have seen, that a simple refrigerant treatment, without reference to the alkalizing of the blood, would not prove equally efficient.*

From its property of rendering the urine alkaline, it may be advantageously employed in cases attended with excessive deposition of the urates in the urine, whether gouty or not; supposing an indication to exist at the same time for an aperient.

The dose as a laxative is from two to four drachms, for full cathartic effect not less than an ounce; care being taken that the salt is dissolved before being administered.

The Seidlitz powder, of which the Rochelle salt constitutes the basis, is a preparation much employed as a gentle aperient. it consists of one powder containing two drachms of this salt and two scruples of bicarbonate of soda in one paper, and another powder of thirty grains of tartaric acid in another paper. The two powders are dissolved separately, the former in about two fluidounces of water, the latter in one fluidounce; and the solutions are then gradually mixed, and taken in the state of effervescence. The tartaric acid unites with the soda of the bicarbonate, of which the carbonic acid escapes, producing the effervescence; and the medicine, as taken, is a mixture of the tartrate of potassa and soda, with tartrate of soda. it is an excellent refrigerant laxative, which has recently been adopted by the U. S. Pharmacopoeia, under the name of Pulveres Effervescentes Aperientes. it is peculiarly adapted to cases in which the stomach is delicate or irritable. The powder may be repeated every four or five hours till it operates; and sometimes advantage will accrue, in cases of great irritability of stomach, or in children, from giving fractions of a dose, repeated more frequently. in such a case, when the powders cannot be duly divided by weight, the object should be effected by dissolving each powder in a certain number of measures of water, and mixing one or an equal number of measures from each solution. To render them more agreeable to the taste, one of the solutions may be sweetened and aromatized before they are mixed.

* See a paper by Dr. John B. Chapin in N. Y. Med. Times (iii. 385, Aug. 1854), detailing the results obtained by Dr. Swett in the N. York Hospital, and another by Dr. John T. Metcalf, in the same journal (v. 1, October, 1855), giving an account of nineteen cases of acute rheumatism under his own care in the same hospital, and sixteen others under the care of Drs. Griscom and Bulkley, in all thirty-five cases, of which only two were not benefited by the treatment.