Page 8 - ALLEN'S COMMERCIAL ORGANIC ANALYSIS A TREATISE ON THE PROPERTIES, MODES OF ASSAYING... VOL II

EXTRACTION AND PURIFICATION. 5

small quantities of material, was devised by West-Knights (Analyst,
1883,8,65). It has the advantage of being readily constructed in the
laboratory. A percolator is made by cutting off the bottom from a
test-tube of suitable size, and blowing a hole or two (A A) in the side
of the tube about an inch from the top. A disc of filter-paper or fine
• cambric (B) is tied over the lower end of the tube. The substance to
be extracted is placed in the tube, and kept in
its place by some glass-wool or a perforated
disc of metal, and the tube with its contents
then fixed by a cork to the lower end of the tube
of a vertical condenser (C). This is fitted by a
larger cork (D) to the neck of an ordinary flask
containing the volatile solvent. On heating
the flask the vaporised solvent passes through
the holes in the side of the test-tube up into the
tube of the condenser, where it is liquefied.
d
The condensed liquid drops back into the test-
tube, percolates through the substance to be
extracted, and falls to the bottom of the flask,
to be again volatilised. As the percolator is
inside the flask, its contents are kept constantly
at the b. p. of the solvent, and, the action being
continuous and automatic, very rapid exhaus-
tion may be effected.
Other forms of exhauster have been con-
trived by Church, Drechsel, Angell, Thoms,
Thresh (Pharm. J., [3] 1884, 15, 281);
Fruhling (Zeit. angew. Chem., 1889, 242).
FIG. 1.
(See also Vol. 1.)
To recover the oil from its solution in the ether or other liquid em-
ployed, the solvent should be distilled off at a steam-heat, and the last
traces of it removed by placing the flask on its side and heating it in the
water-oven until constant in weight. In some cases the complete re-
moval of the solvent is best effected by blowing a gentle stream of air,
previously filtered_through cotton-wool, through the flask while it is
maintained at a temperature of 1oo°.
Large quantities of material may be readily extracted in the ap-
paratus (Fig. 2), which is constructed on the principle of the Szom-
bathy extractor.