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.
[Illustration]