_Tartaric Acid._
QUALITIES. _Form_, Crystals of considerable size, whose primary form is
an oblique rhombic prism; they do not deliquesce when exposed to the
air, but melt at a heat a little exceeding 212°. _Taste_, very acid and
agreeable. SOLUBILITY. Water at 60° dissolves about one-fifth of its
weight, and when boiling, a much greater proportion. The solution,
which, if saturated, has the specific gravity 1·230, acquires, when
diluted, like that of most vegetable acids, a mouldy pellicle by
keeping. The saturating power of crystallized tartaric acid is almost
exactly equal to that of crystallized citric acid, the atomic weight of
the former being 76, and that of the latter 75. CHEMICAL COMPOSITION.
When uncombined with water, as it exists in tartrate of potass, it is
composed of 5 atoms of oxygen, 3 atoms of hydrogen, and 4 atoms of
carbon. The crystals consist of 1 atom of acid and 1 of water.
INCOMPATIBLE SUBSTANCES. Alkalies, Earths, and their carbonates; the
salts of lime and lead. The solutions of the salts of potass are
converted by it into bi-tartrate, or super-tartrate. MEDICINAL USES. It
is introduced into the Pharmacopœia as a cheap and efficient substitute
for the citric acid. It is also used in the preparation of _Sodaic
powders_, _Seidlitz powders_, &c. ADULTERATIONS. When carelessly
prepared it will contain sulphuric acid, to detect which, let a portion
be dissolved in distilled water, and a solution of acetate of lead be
added. A precipitate will appear which, if the acid be pure, will be
entirely redissolved by a few drops of acetic acid, or pure nitric acid.
If any portion remain undissolved, sulphuric acid is the cause. Muriate
of Baryta also, when sulphuric acid is present, but not otherwise, gives
a precipitate insoluble by an excess of muriatic acid.