CHEMICAL COMPOSITION. Oil 60·94, soda 8·56, water 30·50; the water is
partially dissipated by being kept, and the soap therefore becomes
lighter. Muriate of Soda is also an essential ingredient[627] of _hard_
soap. SOLUBILITY. Water dissolves about one-third of its weight of
genuine soap, and forms a milky solution; alcohol also dissolves it, and
affords a solution nearly transparent, although somewhat
gelatinous.[628] INCOMPATIBLE SUBSTANCES. 1. All acids and acidulous
salts, which combine with the alkali, and develope the oil. 2. Earthy
salts, e. g. _Alum_; _muriate_ and _sulphate of lime_; _sulphate of
magnesia_. 3. Metallic salts. _Nitrate of silver_; _ammoniated copper_;
_tincture of muriated iron_; _ammoniated iron_; _acetate_,
_sub-muriate_, and _oxy-muriate of mercury_; _sub-acetate of lead_;[629]
_tartarized iron_; _tartarized antimony_; _sulphate of zinc_, _copper
and iron_. 4. All astringent vegetables. 5. Hard water. MEDICINAL USES.
In large doses it is purgative; in smaller ones, it is decomposed _in
transitu_, and its alkali is carried to the kidneys; in this way it may
act as a lithonthriptic; or it may produce its effects by correcting any
acidity which may prevail in the _primæ viæ_, for the weakest acid is
capable of decomposing soap, and of uniting with its alkaline base; a
solution of soap in lime water was long regarded as one of the strongest
solvents of urinary calculi that could be administered with safety, but
the result of such a mixture is an insoluble soap of lime, and a
solution of soda; in habitual constipation, and in biliary obstructions,
it is frequently prescribed in conjunction with rhubarb, or some bitter;
in which cases it can only act as a laxative, or as a chemical agent, in
increasing the solubility of the substance with which it is united. It
has been also given in solution as an antidote to metallic poisons, and
it is often successfully injected as a clyster, in unrelenting and
habitual costiveness; as an external application, it is used in the form
of liniment, (see _Linimenta_.) Its pharmaceutical value, in forming
pill-masses, has already been considered (_page 196_), and the following
_formulæ_ afford examples of such an application, viz. 14, 80, 105, 118,
165. OFFICINAL PREPARATIONS. _Pil. Saponis cum Opio_. L. (=L=). _Pil.
Scillæ comp_. _L._ (=M=). _Pil. Aloet_. E. (=L=). _Pil. Aloes et
Assafœtidæ_. E. (=I=). _Pil. Aloes cum Zinzib_. D. (=L=). _Pil.
Colocynth. comp_. D. (=L=). _Emplast. Saponis_. L.E. _Ceratum Saponis_.
L. _Liniment. Saponis. comp_. L. _Liniment. Saponis cum Opio_. L.
ADULTERATIONS. Pulverized Lime, Gypsum, or Pipe clay, are sometimes
added; but the fraud is easily detected by solution in alcohol, when the
earthy matters fall down.