In this preparation, alcohol is nearly in the highest state of
concentration, in which it can be easily prepared in the large way for
the purposes of trade; its specific gravity however varies in the
different pharmacopœias, viz. the London and Edinburgh preparation is
stated to have that of ·835, while the rectified spirit of Dublin is
ordered to be only ·840. The former at the temperature of 60° _Fah._
consists of 85 parts of pure alcohol and 15 of water, the latter only of
83 per cent. of alcohol. It is a most powerful stimulant, but is rarely
employed except in combination; as a pharmaceutical agent, its use is
highly valuable and extensive. (See _Tincturæ_.) During the evaporation
of spirit, a considerable reduction of temperature takes place, which
renders it a useful ingredient in refrigerating lotions. See _Form. 147,
148_. It has lately been ascertained by Mr. Ritchie of Perth, that “_the
degree of cold induced by the evaporation of spirit of different degrees
of strength are proportional to the strength of these spirits, reckoning
from the degrees of cold induced by the evaporation of water_.” The
application of this theorem will enable us to ascertain the strength of
a spirit by the “DIFFERENTIAL THERMOMETER” of Leslie.