This fluid is formed from the decomposition of the resinous juice of the
pine, during the slow and smothered combustion of its branches, and as a
summary definition of the substance, that by Pliny cannot be surpassed,
“_Pix nihil aliud quam combustæ resinæ fluxus._” _Lib. 23. c. 1._
CHEMICAL COMPOSITION. It is found to consist of empyreumatic oil, resin,
acetic acid, and some salts. SOLUBILITY. Water readily dissolves a
portion of Tar, and forms a solution of the colour of Madeira wine, with
a sharp empyreumatic taste. MED. USES. Tar water, under the auspices of
Bishop Berkley, was formerly considered a remedy of extraordinary
powers;[600] this opinion however has at length passed away, (_see page
27_.) and Tar is now particularly indebted for a place in the Materia
Medica, to an essay by Sir Alexander Crichton, entitled, “_An Account of
some Experiments made with the Vapour of boiling Tar,[601] in the cure
of Pulmonary Consumption_.” At the request of Sir Alexander, I was
induced to make a trial of its effects, and I do not feel any hesitation
in stating that the result has led me to believe that it may, in some
cases, be attended with benefit. In the application of the remedy
several precautions are necessary for its success. The Tar employed
should be that used in the cordage of ships; to every pound of which
half an ounce of sub-carbonate of potass must be added, in order to
neutralize the pyroligneous acid generally found mixed with the tar, the
presence of which will necessarily excite coughing; the tar thus
prepared is to be placed in a suitable vessel over a lamp, and to be
kept _slowly_ boiling in the chamber during the night as well as the
day; the vessel however ought to be cleaned and replenished every
twenty-four hours, otherwise the residuum may be burnt and decomposed, a
circumstance which will occasion increased cough and oppression on the
chest. The ancients entertained a high opinion of the efficacy of Tar in
pulmonary diseases, when internally administered; supposing it to
promote expectoration, relieve dyspnæa, and check spitting of blood;
Dioscorides particularly speaks of its utility in such cases; he also
recommends it to be applied to ulcers, which he says it fills up and
heals, whether they be situated on the surface of the body, or in the
ears, throat, and other internal parts. See the chapter on
“_Inhalations_,” _page 202_. OFFICINAL PREP. _Unguent._ _Picis Liquidæ._
L.