"Take of bitartrate of potassa, four pounds; boiling distilled water, two gallons and a half; prepared chalk, twenty-five ounces and six drachms; diluted sulphuric acid, seven pints and seventeen fluid ounces; hydrochloric acid, twenty-six fluid ounces and a half or as much as may be sufficient. Boil the bitartrate of potassa with two gallons of the distilled water, and gradually add half the prepared chalk, and when the effervescence has ceased, add the remainder of the chalk dissolved in the hydrochloric acid with four pints of distilled water: set the mixture apart, that the tartrate of lime may subside; pour off the fluid, and wash repeatedly the tartrate of lime with distilled water, until it come off tasteless. Then pour upon it the diluted sulphuric acid, and boil for a quarter of an hour. Filter the liquor, and evaporate it in a water-bath, to obtain the crystals." Dissolve the crystals again, and a third time in water that they may be pure, and strain the solution as often; boil it down and set it aside.

Dublin. "Take of bitartrate of potassa rubbed into powder, ten parts; prepared chalk, four parts; sulphuric acid, seven parts; water, one hundred and twenty parts. Mix the bitartrate of potassa with one hundred parts of the water at a boiling temperature; gradually add the chalk; and when the effervescence is over, pour off the limpid supernatant liquid. Wash the residue, which is tartrate of lime, until it is tasteless. Pour into the decanted liquor as much solution of muriate of lime as will precipitate the tartrate of lime it may hold suspended, and having washed this also with water until it becomes tasteless, mix it with the prior precipitate. Then add the sulphuric acid diluted with the twenty parts of water, and digest the mixture in a medium heat for three days, frequently stirring. The liquors, as well the acid liquor as that employed for washing, evaporate, by a moderate heat, to crystallization. Purify the crystals by repeated solutions and crystallizations, and keep them in a closely-stopped glass bottle."

In these processes, which are nearly the same as that of Scheele, the lime of the chalk separates the excess of tartaric acid from the potassa with which it was previously combinedl; and again yields it up, in order to combine with the sulphuric acid, which is used in the second part of the process. The use of the hydrochloric acid is to form with the chalk a chloride of lime, which decomposed the tartrate of potassa, so that the whole of the tartaric acid is thus procured. Before crystallizing, it is proper to test the liquor by dropping a little acetate of baryta into a small portion of it, which throws down a precipitate insoluble in nitric acid, if any sulphuric acid be present; in which case a little more tartrate of lime should be added. The crystals are obtained in groups, and cannot be always procured of the same form under the most careful management. The process is not adapted for operations on a small scale, and indeed may be regarded as an incumbrance of the Pharmacopoeia, as much better tartaric acid can be purchased at a moderate price, prepared in the large way.

1 The components of bitartrate of potassa are, tartaric acid 70.15, potassa 25.13, and water 4.72, in 100 parts.

Qualities. - Tartaric acid in its crystallized state is white, imperfectly transparent, persistent in the air, inodorous, and very acid to the taste. The primary form of its crystal is an oblique rhombic prism.1 It melts when heated a little above 212°, and boils at 250°, without losing its whiteness, and unless the boiling be long continued, it loses little more than 4 per cent of its weight: but the nature of the acid is changed; for on cooling, the semi-transparent mass into which it concretes is deliquescent. Tartaric acid is readily soluble in water, which dissolves one fifth of its weight, at 60° Fah. and twice its weight at 212°; and the saturated solution is not soon liable to spontaneous decomposition. It is, also, partially soluble in alcohol. It is decomposed by a high temperature, and also by sulphuric and nitric acids, the latter of which converts it into oxalic acid. It combines with alkalies, earths, and metallic oxides, forming tartrates; and in its power of saturating alkalies closely resembles citric acid.

According to the analysis of Berzelius, 100 parts of this acid, as it exists in tartrate of potassa, are composed of 3951 of hydrogen, 36.167 of carbon, and 59.882 of oxygen, or of five equivalents of oxygen = 40 + 4 of carbon = 24.48 + 2 of hydrogen = 2, making the equivalent 66.48: but, in its ordinary crystallized state, or as a hydrate, it is composed of 88.16 parts of real acid, and 11.84 of water, in 100 parts, or of one eq. of dry acid = 66.48+ 1 of water = 9 equiv. = 75.48. When carelessly made, it may contain sulphuric acid, which, however, can be detected by adding chloride of barium to a weak solution, when a precipitate insoluble in an excess of nitric acid will be thrown down, if sulphuric acid be present. One hundred grains of the crystallized acid saturate 200 grains of crystallized carbonate of soda.

1 Phillips's Trans, of Pharm. 1824.

Medical properties and uses.- Tartaric acid, largely diluted and sweetened, forms a cooling agreeable beverage in fevers and diseases connected with an increased secretion of bile. It is incompatible in prescriptions with solutions of salts containing potassa, which it converts into a bitartrate, which being of difficult solution is thrown down in minute crystals. It also precipitates salts of lime and of lead. Dissolved in water, and added to an aqueous solution of carbonate of soda, it forms a good substitute for soda-water.

Officinal preparations. - Potassae Tartras, L. E. D. Sodae Po-tassio-tartras, L. Antimonii Potassio-tartras, L. E. D. Ferri Potassio-tartras, L. E. D.