3929. Tartaric Acid

3929. Tartaric Acid. Tartaric acid forms inodorous, sour, scarcely transparent prisms, soluble in 2 parts of water at G0°, and its own weight of boiling water. It contains about 9% of combined water, fuses at 220° Fahr., boils at 280°; and, at about 400°, after losing 1/4 of its water, is converted into tartralic acid. "With the bases it forms salts called tartrates. Tartaric acid is chiefly employed in calico printing, and in medicine, as a substitute for citric acid and lemon juice, for the preparation of cooling drinks and saline draughts.

3930. To Obtain Tartaric Acid

3930.    To Obtain Tartaric Acid. On the small scale it is prepared as follows : Dissolve 4 pounds cream of tartar in 2 gallons boiling water; add gradually 12 ounces 7 drachms chalk; and, when the effervescence ceases, add another like portion of chalk, dissolved in 261/2 fluid ounces muriatic acid, diluted with 4 pints water; collect the precipitated tartrate of lime, and well wash it with water, then boil it for 15 minutes in 8 pints 1 fluid ounce dilute sulphuric acid; next filter, evaporate to the density 1.38, and set it aside to crystallize. The crystals must be dissolved and crystallized a second and a third time.

On the largo scale, the decomposition of the tartar is usually effected in a copper boiler, and that of tho tartrate of lime in a leaden cistern. This part of the process is often performed by mere digestion for a few days, without tho application of heat. Leaden or stoneware vessels are used as crystallizers. Good cream of tartar requires 26 per cent, of chalk,-and 28.5 per cent, of dry chloride of calcium for its perfect decomposition. Dry tartrate of lime requires 75 per cent, of oil of vitriol to liberate the whole of the tartaric acid. A very slight excess of sulphuric acid may be advantageously employed. Some manufacturers bleach the colored solution of the first crystals by treating it with animal charcoal; but for this purpose the latter substance should be first purified by digesting it in muriatic acid, and afterwards by edulcorating it with water, and exposing it to a dull red heat in a covered vessel. The general management of this manufacture resembles that of citric acid. (Cooley.)

3931. To Detect Tartaric Acid in Citric Acid

3931.      To Detect Tartaric Acid in Citric Acid. Citric acid is sometimes adulterated with tartaric acid. This is readily detected by adding a solution of carbonate of potassa to a solution of the suspected acid; if tartaric acid be present, a crystalline precipitate of bitartate of potassa (cream of tartar) will bo found. A more delicate test is to digest the suspected acid with hydrated sesqui-oxide of iron in a test tube, and afterwards to raise the heat slowly to the boiling point; allowing the excess of oxide to subside, decant the clear liquid, and evaporate it to a syrupy consistence. If the citric acid was pure, the liquid remains clear and of a fine red color; the presence of only 1 per cent, of tartaric acid renders it cloudy, and deposits tartrate of the sesquioxide. ( U. S. Dis.)