Prep. From the acid or bitartrate of potash (cream of tartar) by the addition of chalk, whereby an insoluble tartrate of lime is formed with half the acid in the bitartrate, and a neutral tartrate of potash left in solution; the acid of which is afterwards likewise formed into tartrate of lime by decomposition of the potash salt with chloride of calcium. Lastly, tartaric acid is separated from the purified tartrate of lime by decomposition with sulphuric acid. The formulas representing the decompositions which occur in the above process may be thus exhibited: 1st part of process, -
2 (HO, KO, C3 H4 O10) + 2 (Ca O, C02)=(2 Ca O, C8 H4 O10) + (2 KO, C8 H4 O10)+Co2+2 HO. 2nd part of process, -
(2 KO, C8 H4 O10) +2 (Ca Cl)=(2 Ca O,C8 H4 O10) + 2 (K CI.) 3d part of process, -
2 (2 Ca O, C8 H4 O10) + 4 (HO, S03)=2 (2 HO, C8 H4 O10) +
4 (Ca 0, So3).
Prop. & Comp. Tartaric acid occurs in white transparent crystals, which are oblique rhombic prisms, with a sour but agreeable taste, decomposed entirely by heat, soluble in water and in rectified spirit, the solution precipitating bitartrate of potash from any neutral salt of potash. The solution should not give a precipitate with chloride of barium, and any precipitate thrown down with acetate of lead should be soluble in nitric acid. 75 grains (half the equivalent in grains of tartaric acid, as this acid is bi-basic) dissolved in water require for saturation 100 measures of the volumetric solution of soda.
Therapeutics. Tartaric acid acts in the same way as citric acid, as a refrigerant in fevers, diminishing thirst: it is more commonly given for such purposes in the form of cream of tartar, or with bicarbonate of soda, in an effervescing state.
Pose. 10 gr. to 30 gr. or more, dissolved in water and sweetened.
Adulteration. Sulphuric acid may be present from imperfect preparation. Bitartrate of potash and alum have occasionally been added.
The following are the tests for purity in the Pharmacopoeia. The aqueous solution of tartaric acid is not affected by sulphuretted hydrogen, and gives no precipitate with the solution of sulphate of lime or of oxalate of ammonia; leaves no residue, or merely a trace, when burned with free access of air; these tests indicate the absence of oxalic acid, lime, or other fixed impurities.
Oxalic Acid. Appendix. [Not Officinal in U. S. P.]
The Oxalic Acid of Commerce is directed to be purified, by dissolving one pound of it in thirty fluid ounces of boiling water, filtering and crystallizing the acid from the filtered solution.
Prop. & Comp. Oxalic acid forms transparent four-sided prisms, soluble in water and alcohol. Its composition is represented by the formula, HO, C2 03 + 2 HO. It is entirely dissipated by a heat below 350°.
Use. The solution of oxalic acid is used for quantitative and qualitative analysis.