_Kali Vitriolatum_, P.L. 1787.
_Tartarum Vitriolatum, 1745, and 1720._
_Sal de duobus_, &c.
QUALITIES. _Form_, crystals which are right rectangular (but not square)
prisms, modified on the edges and angles; or double six-sided pyramids
with short intervening prisms, which are macles, or hemitrope crystals;
they are slightly efflorescent, and when heated they decrepitate.
SOLUBILITY. f℥j of water dissolves only grs. 24: the salt is insoluble
in alcohol. INCOMPATIBLE SUBSTANCES. It is partially decomposed by the
nitric and muriatic acids, in which case, a portion of the base being
saturated, a corresponding portion of _bi-sulphate_ results; this fact
illustrates a chemical law of some importance, viz. _that a substance
less weakly attracted by another than a third, will sometimes
precipitate this third from its combination with the second, in cases
wherein a_ super, _or_ sub-_salt is readily formed_.[611] The history of
tartrate of potass will furnish farther illustrations. See _page 183_.
Sulphate of potass, when in solution, is entirely decomposed by _lime_
and _its compounds_; by _oxy-muriate of mercury_; _nitrate of silver_;
and by _acetate_ and _sub-acetate of lead_. MED. USES. On account of its
insolubility, it does not possess much activity as a purgative, but is
said to be powerfully deobstruent; it should be exhibited in the form of
powder, and in conjunction with rhubarb, or some other purgative
medicine. DOSE, grs. x to ℥ss. _Form. 94._ From its hardness and
insolubility, it is a most eligible substance for triturating and
dividing powders. OFFICINAL PREP. _Pulv. Ipecac. co._ L.E.D. (=M=) Under
the name _Sulphas Potassæ cum Sulphure_, the Edinburgh college retains
the preparation formerly known by the name _Sal Polycrest_ (_Salt of
many virtues_); and as it is produced by deflagrating nitre with
sulphur, the product, besides sulphate of potass, contains _bi-sulphate_
and _sulphuret of potass_. It possesses no superiority over the common
sulphate.