All about coffee by William H. Ukers

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.