According to McGill, a 10-percent extract of pure coffee has a specific gravity of 1.00986 at 15° 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, nd 20° = 1.3377.
With a 10-percent chicory extract, nd 20° = 1.3448.
Determinations of the solids, ash, sugar, nitrogen, etc., may be made in the 10-percent extract, if desired.
24. Caffetannic Acid—Krug's Method[187]
Treat 2 grains of the coffee with 10 cc. of water and digest for 36 hours; add 25 cc. of 90-percent alcohol and digest 24 hours more, filter, and wash with 90-percent alcohol. The filtrate contains tannin, caffein, color, and fat. Heat the filtrate to the boiling point and add a saturated solution of lead acetate. If this is carefully done, a caffetannate of lead will be precipitated containing 49 percent of lead. As soon as the precipitate has become flocculent, collect on a tared filter, wash with 90-percent alcohol until free from lead, wash with ether, dry and weigh. The precipitate multiplied by 0.51597 gives the weight of the caffetannic acid.
