n a special
heating stage used in connection with a microscope.

The chief commercial source of this alkaloid is waste and damaged tea,
from which it is prepared by extraction with boiling water, the tannin
precipitated from the solution with litharge, and the solution then
concentrated to crystallize out the caffein. It is further purified by
sublimation or recrystallization from water. Coffee chaff and
roaster-flue dust have been proposed as sources for medicinal caffein,
but the extraction of the alkaloid from the former has not proven to be
a commercial success. Several manufacturers of pharmaceuticals are now
extracting caffein from roaster-flue dust, probably by an adaptation of
the Faunce[134] process. The recovery of caffein from roaster-flue gases
may be facilitated and increased by the use of a condenser such as
proposed Ewe.[135]

Pure caffein forms long, white, silky, flexible needles, which readily
felt together to form light, fleecy masses. It melts at 235-7 deg. C. and
sublimes completely at 178 deg. C., though the sublimation starts at 120
deg. Salts of an unstable nature are formed with caffein by most acids. The
solubility of caffein as determined by Seidell[136] is given in Table I.

TABLE I--THE SOLUBILITY OF CAFFEIN

Solubility:
Grm. Caffein
per 100
Grm. of Sp. Gr. of
Sp. Gr. of Temperature Saturated Saturated
Solvent Solvent of Solution Solution Solution

Water 0.997 25 2.14
Ether 0.716 25 0.27
Chloroform 1.476 25 11.0
Acetone 0.809 30-1 2.18 0.832
Benzene 0.872 30-1 1.22 0.875
Benzaldehyde 1.055 30-1 11.62 1.087
Amylacetate 0.860 30-1 0.72 0.862
Aniline 1.02 30-1 22.89 1.080
Amyl alcohol 0.814 25 0.49 0.810
Acetic acid 1.055 21.5 2.44
Xylene 0.847 32.5 1.11 0.847
Toluene 0.862 25 0.57 0.861

The similarity between caffein and theobromin (the chief alkaloid of
cocoa), xanthin (one of the constituents of meat), and uric acid, is
shown by the accompanying structural formulae.

These formulae