_Muriatic Acid._
QUALITIES. _Form_, a liquid of the specific gravity 1·16, a fluid-ounce
of which weighs about 527 grains, and according to Dr. Powell ought,
when diluted, to dissolve 220 grains of limestone. _Odour_, strong and
pungent; if exposed to the air it emits white fumes. _Taste_, intensely
sour and caustic; it is however the weakest of the three mineral acids;
and no remarkable elevation of temperature is produced by dilution.
CHEMICAL COMPOSITION. The liquid acid is a solution of muriatic acid gas
in water; when of the specific gravity 1·16, according to Davy, it
contains 32·32 per cent of the gas, which recent experiments have shewn
to be a compound of _Chlorine_ (_Oxy-muriatic acid)_ and hydrogen in
equal volumes. It has therefore received a name expressive of its
composition, and is called _Hydro-chloric[348] acid_. We accordingly
find that the former element is disengaged from muriatic acid by adding
any substance capable of uniting with its hydrogen. For the purpose of
obtaining _Chlorine_, we may take three parts of common salt, one of
black oxide of manganese, and rather less than three of strong sulphuric
acid.[349] Accounts have been received from Spain, that in the midst of
the dreadful contagion which reigned in that country, the inhabitants
always escaped in those houses where fumigations of chlorine had been
used. In our own country, the Penitentiary has lately undergone
fumigation by this gas, under the superintendance of Mr. Faraday.[350]
Muriatic acid gas has also been strongly recommended for the same
purpose; it may be easily evolved by pouring sulphuric acid on common
salt. If nitric and muriatic acids be mixed, a mutual decomposition
takes place, of which water, chlorine, and nitrous acid are the results;
this constitutes “nitro-muriatic acid,” the _Aqua regia_ of the older
chemists. A bath acidulated with an acid of this kind has been
recommended by Dr. Scott, as a powerful remedy for diseases of the liver
in particular, and as a substitute for mercury in general. On the
possible influence of this bath, I would beg to make one
observation,—that the extensive application of a dilute acid to the
surface of the body, is, under certain circumstances, capable of
affecting the bowels. I have witnessed such an effect from sponging with
vinegar and water. In this way the acidulated bath may occasionally
produce benefit, but it is extremely difficult to conceive how it can be
indebted for its utility to any other mode of operation. (See _Journal
of Science and the Arts_, No. 2.) FORMS OF EXHIBITION. Muriatic acid
should be administered in some bland fluid, as barley water, gruel, &c.
(_Formula 145._) I have uniformly exhibited it with success in the most
malignant cases of typhus and scarlatina, during several years extensive
practice in the Westminster Hospital. See _page 157_. We should be
careful not to apportion its dose in a leaden or pewter spoon. The
antiseptic properties of this acid have been long known; Sir Wm. Fordyce
relates that a “dry-salter” acquired a large fortune from possessing a
secret that had enabled him to send out provisions to India in a better
state of preservation than any others of the trade; his secret consisted
in adding a small quantity of muriatic acid to the contents of each
cask. After a copious evacuation of the bowels, it is in my experience
the most efficacious remedy for preventing the generation of worms; for
which purpose the infusion of quassia, stronger than that of the
Pharmacopœia, is the best vehicle. DOSE, ♏︎v-xx, frequently repeated. It
may be here observed that where the permanent influence of an acid is
required, a mineral one should be always preferred, as such bodies
appear to be beyond the control of the digestive process,[351] and are
incapable of being decomposed by it; see _Form. 158_, whereas on the
contrary it seems probable that the organs of assimilation have command
over those of a vegetable nature, and generally decompose them. Dr.
Marcet has very judiciously noticed this fact in his luminous work on
the treatment of calculi, and I have ventured to offer some farther
observations upon this subject, which may be of practical value, under
the consideration of _Lithonthryptics_, page 123. ADULTERATIONS.
_Sulphuric acid_ is detected by diluting the acid with six parts of
distilled water, and adding a few drops of the muriate of baryta, which
occasions a white precipitate if any be present. _Iron_, by saturating a
diluted portion with pure carbonate of soda, and adding prussiate of
potass, which will indicate its presence by a blue precipitate; or by a
solution of ammonia, which, when added slightly in excess, throws down
the peroxide of iron of a reddish yellow colour. _Copper_, by the
production of a blue colour when supersaturated with ammonia. The yellow
tinge of the acid usually met with in commerce, may depend either upon
the presence of iron, vegetable extractive, or a small portion of
chlorine. This latter body may be recognised by the odour, or by its
power of dissolving gold leaf.