Weigh into a tared flask the equivalent of 10 grains of the dried
substance, add water until the contents of the flask weigh 110 grams,
connect with a reflux condenser and heat, beginning the boiling in 10 to
15 minutes. Boil for 1 hour, cool for 15 minutes, weigh again, making up
any loss by the addition of water, filter, and take the specific gravity
of the filtrate at 15째 C.
According to McGill, a 10-percent extract of pure coffee has a specific
gravity of 1.00986 at 15째 C., and under the same treatment chicory gives
an extract with a specific gravity of 1.02821. In mixtures of coffee and
chicory the approximate percentage of chicory may be calculated by the
following formula:
(1.02821 - sp. gr.)
Percent of chicory = 100 ------------------
0.01835
The index of refraction of the above solution may be taken with the
Zeiss immersion refractometer or with the Abbe refractometer.
With a 10-percent coffee extract, n_d 20째 = 1.3377.
With a 10-percent chicory extract, n_d 20째 = 1.3448.
Determinations of the solids, ash, sugar, nitrogen, etc., may be made in
the 10-percent extract, if desired.