_Nitre_ or _Salt Petre_.
QUALITIES. _Form_, crystals which are six-sided prisms usually
terminated by dihedral summits. _Taste_, bitter and sharp with a
sensation of cold. CHEMICAL COMPOSITION. It consists of one proportional
of nitric acid, and one proportional of potass. SOLUBILITY. It dissolves
in seven parts of water at 60°, and in its own weight at 212°. Its
solubility is considerably increased by adding muriate of soda to the
water; its solution is attended with a great reduction of temperature;
it is quite insoluble in alcohol. INCOMPATIBLE SUBSTANCES. _Alum_;
_sulphate of magnesia_; _sulphuric acid_; _the sulphates of zinc,
copper, and iron_; according to the usual laws of affinity, it should be
also decomposed by _sulphate of soda_; this however only takes place at
the temperature of 32°, and then but partially. MED. USES. Refrigerant,
in which case the draught should be swallowed immediately after the
solution of the salt is complete, for if it be allowed to stand for some
time, its effect with regard to cooling is not nearly so evident (see
_Form. 138, 144_); as a diuretic, its powers are too inconsiderable to
be employed, except in combination (_Form. 102, 109, 115, 170_); a
solution of ʒj to f℥vj of rose water forms a good detergent gargle, and
a small portion allowed to dissolve slowly in the mouth, will frequently
remove an incipient inflammation of the tonsils: for its _modus
operandi_ as a diuretic, see _Potassæ Acetas_. DOSE, grs. x to xv, as a
diuretic or refrigerant; grs. xxv to xl are aperient, and in large doses
it excites vomiting, bloody stools, convulsions, and even death. The
best antidotes are opium and aromatics. IMPURITIES. As it occurs from
the hand of nature it is far from pure, and even by art it is freed with
difficulty from sea salt; the presence and quantity of which in any
specimen, may be learnt by adding nitrate of silver to its solution as
long as any precipitate is produced.