Chap. XXXV. Of Extracts and Resins.

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yielded to cold water 30 parts, then to boiling water 9, and,lastly, to alcohol 7. The first solution or cold infusion wasof a deep brownish-red colour, remained transparent, andsmelt strongly of opium ; the second or decoction was of apale brown colour, deposited on cooling the greater part ofwhat had been dissolved, and had no smell of opium ; and thethird or tincture very much resembled common tincture ofopium, and furnished, on the addition of water, an abundantyellowish-white precipitate. Dr Powell also says, that proof-spirit by heat dissolves 9-12ths of opium; and water, althoughheated, only 5-12ths.

Cinchona bark is a medicine of very great importance;but, unfortunately, the proportion of woody fibres, or inertmatter, which enters into its composition, is so great, that weakstomachs cannot bear it, when given in quantity sufficient toproduce any very powerful effects. On this account the pre-paration of an extract, which may contain its active princi-ples in a concentrated form, is a desirable object. On thissubject there is still much room for experiment. The Lon-don college, in its former Pharmacopoeia, certainly erred in twoimportant particulars ; in the first place, in desiring the de-coction to be continued until the greatest part of the men-struum was evaporated; and, in the second place, in separating,by filtration, the powder which separated from the decoctionafter it had cooled. The first error probably originated inthe idea, that, by continuing the boiling for a great length oftime, more of the bark would be dissolved ; but it is nowknown, that water is incapable of dissolving more than a cer-tain quantity of the active principles of cinchona ; and thatafter the water has become saturated, by continuing the de-coction we diminish the quantity of the menstruum, andtherefore also diminish the quantity of bark dissolved. It isnot easy to account for the second error; for, according tothe old idea, that the powder which separated, on cooling,from a saturated decoction of cinchona, was a resinous sub-stance, it surely ought not to have been rejected from whatwere supposed to be resinous extracts. This precipitate isnow known to be caused by the much greater solubility of itsactive principles in boiling than in cold water; so that theprecipitate is not different from what remains in solution.Accordingly, I ascertained, by experiment, that cinchona gaveat least one half more extract when the decoction was con-ducted according to the directions of the Edinburgh college;and the London college, in their present Pharmacopoeia, haveimproved their processes on the same principles.