_Super-Tartrate of Potass._ _Crystals of Tartar._
QUALITIES. _Form_, small irregular brittle crystals, which when reduced
to powder are termed _cream of tartar_. _Taste_, harsh and acid.
CHEMICAL COMPOSITION. It is a _bi-tartrate_, consisting of two
proportionals of acid and one proportional of potass. _Solubility._ It
requires 120 parts of water at 60°, and 30 parts at 212°, for its
solution; it is slightly soluble in alcohol. The watery solution of this
salt was first observed by Berthollet to undergo a spontaneous
decomposition by keeping, during which a mucous matter is deposited, and
there remains a solution of carbonate of potass coloured with a little
oil. It has long been regarded a pharmaceutical desideratum to increase
the solubility of _cream of tartar_; Vogel discovered that it might be
accomplished by combining it with boracic acid, and accordingly a
formula has been introduced into the Codex Medicamentarius of Paris, for
preparing a “_Tartras Acidulus Potassæ Solubilis, admixto Acido
Boracico_.” The following is the process. Let thirty parts of boracic
acid, and twenty parts of distilled water be heated together in a silver
dish; as soon as this has been effected, add, in divided portions, 120
parts of super-tartrate of potass, taking care to shake the mixture
continually; the whole will soon liquefy, (“_mire liquescent_,”) and by
continuing the heat, a pulverulent mass will result. As it is extremely
deliquescent it must be carefully preserved from the contact of the air;
it dissolves in its own weight of water at 55°, and in half its weight
at 212°. It is probable that the result is a new salt, in which the
boracic and tartaric acids exist in combination,[614] but grant even
that the chemical identity of the super-tartrate is preserved inviolate
in the compound, I would ask what medical advantage can possibly attend
the discovery? The peculiar value of cream of tartar depends doubtless
upon its comparative insolubility, as I have already stated at page 173;
modify this, and you will instantly change the medicinal effects of the
salt; for like the neutral tartrate it will act upon the bowels, and
therefore cease to undergo those changes _in transitu_ which are
essential to its characteristic operation. Alum also has been observed
by Berthollet to have in some measure the same effect in increasing the
solubility of cream of tartar. INCOMPATIBLE SUBSTANCES. _Alkalies_ and
_alkaline earths_; the _mineral acids_, &c. MED. USES. In doses of ʒiv
to ʒvj, it acts as a hydragogue cathartic, producing a considerable
discharge of serous fluid into the intestines; when however it is often
repeated, it is liable to occasion debility of the digestive organs, and
consequent emaciation: in smaller doses it acts as a diuretic. (_Form.
112._) ʒj in oj of boiling water, flavoured with lemon peel and sugar,
forms when cool an agreeable beverage well known by the name of
_Imperial_. A _Cream of Tartar Whey_ may be made, by adding to a pint of
milk (when it begins to boil) ʒij of _Cream of Tartar_; the pan must
then be removed from the fire, the whole suffered to cool, and the
_whey_ separated from the curd by straining; this whey, diluted with
warm water, furnishes an excellent drink in Dropsy. As it decomposes the
carbonate of potass, the union of these salts will afford a very
pleasant purgative draught. (_Form. 82._) OFFICINAL PREPARATIONS. _Pulv.
Jalap. comp._ E. (=BM=) _Pulv. Scammon_. E. _Pulv. Sennæ comp._ L.
_Ferrum Tartarizatum_, L. (=I=) _Antimonium Tartarizatum_ L.E. D. (_I_)
_Soda Tartarizata_, L.E.D. (=I=) ADULTERATIONS. Super-sulphate of potass
(_Sal Enixum_,) is the substance with which tartar is usually
adulterated; it may be detected by its superior solubility, and by the
solution affording with muriate of baryta a precipitate insoluble in
muriatic acid.[615]