130 THE CHEMISTEY OF ESSENTIAL OILS
is collected on an ignited asbestos filter, washed with 70 per cent,
alcohol, and dried at 100°. The weight of the precipitate is approxi-
mately equal to that of the colophony present.
The following rough method gives an approximate estimate of the
amount of adulteration, if this is colophony, heavy petroleum oil, or a
fixed oil. Weigh 50 grms. of the oil into a small Wurtz flask, and con-
nect in the usual way to a condenser, and gradually heat with a naked
flame. The oil commences to boil at about 210°, and the bulk distils
over between 240° and 260°. When the thermometer rises to 280° and
white vapours rise the distillation is stopped.
On cooling the flask (whose weight is known) its contents are
weighed; the residue should not exceed 10 per cent.—it is seldom more
than 8 per cent.—and should not solidify. Over 10 per cent, residue
indicates adulteration, and if this residue solidifies colophony is present.
The most important method of examination, however, is the deter-
mination of the percentage of cinnamic aldehyde, and upon this per-
centage commercial oils are always sold on the market. In this process
the following details should be observed. Ten c.c. of the oil are run
into a Hirschsohn flask (capacity about 100 to 150 c.c., with a neck
about 5 ins. long and ^ in. in diameter, graduated in TVth c-c.). The
flask is then filled about three-quarters full with a 30 per cent, solution
of sodium bisulphite, and the whole well shaken. The flask is then
placed in the water-bath for several hours with occasional shaking,
until the precipitated compound of the aldehyde and bisulphite is
completely dissolved, and only a clear oil floats on the surface. Bisul-
phite solution is then carefully poured in until the oil is driven up into
the neck, and when it has attained the temperature at which the oil was
measured, the amount is read off. This gives the percentage of non-
aldehydic constituents, the difference being returned as cinnamic alde-
ihyde. Pure oils should not give much less than 85 per cent, of
aldehyde, the best oils yielding 85 to 90 per cent., or occasionally even
-higher. Strictly speaking,, these percentages are by volume, but the
errors of reading the result, and those due to solubility of the non-
.aldehydes in the aqueous liquid render any correction for* the specific
gravity of the constituents unnecessary in practice. Care must be
taken that every particle of the aldehyde compound is dissolved, as
•otherwise the reading of the oily layer will be obscured, and a serious
•error may be introduced. If the precipitate does not dissolve after
standing three hours in the water-bath with repeated shaking, the pre-
sence of solid resin may be inferred, and the estimation of the aldehyde
in this way, with accuracy, is then impossible. Hirschsohn recom-
mends shaking the oil in a graduated tube with three times its volume
of light petroleum ether. A diminution in volume of the oil indicates
petroleum, resin or fatty oils (except castor oil). An increase in
volume of the oil indicates castor oil. The petroleum layer is then
shaken with copper hydroxide. A blue solution indicates copaiba or
resin.
Hanus
1
publishes a new method for the determination of cinnamic
aldehyde in cassia and cinnamon oils depending on the combination of
the aldehyde with semioxamazide. Ten grms. of finely powdered hy-
idrazine sulphate are dissolved in a solution of 9 grms. of caustic soda
l
Pharm. Central, 1904, 37.