The official Resins, with a single exception, constitute a peculiar class of preparations, made by exhausting the substances from which they are obtained by alcohol, and then precipitating the resinous matter from the tincture by the addition of water, which abstracts the alcohol by its stronger affinity. It is obvious that the resins thus prepared are different substances from the alcoholic extracts, which contain all the ingredients of the medicine which alcohol is able to take from it. This set of substances has been much employed by the practitioners styling themselves "eclectics," but with great lack of discrimination. They have applied names to these resinous precipitates which, in their proper scientific use, are employed to designate neutral proximate principles of plants, generally representing more or less completely the effects of the plants respectively on the system; as we say columbin, quassin, santonin, etc., themselves proper proximate principles, and representing the virtues, in part at least, of calumba, quassia santonica, etc., from which they are obtained, and from which they derive their names. By applying similar names to their precipitated resins, such as podophyllin, iridin, cimicifugin, etc., i.e., to the impure resins obtained by precipitating the tinctures of Podophyllum, iris versicolor, cimicifuga, etc., they justify the suspicion either that they ignorantly believe them to be in fact the active principles of these medicines respectively, or that, knowing better themselves, they seek to impose such a conviction upon the ignorant. The fact is that the substances thus obtained, and thus named, are impure resins, which may possibly contain more or less of the active principles mixed with them, but are not entitled to names which imply that they are distinct proximate principles themselves.
Resins are solid, brittle, of a smooth and shining fracture, or in powder and generally of a yellowish-brown color. When perfectly pure, they are probably inodorous and often insipid; but, as usually found, they have a slight odor, and a somewhat acrid or bitterish taste. Their sp. gr. varies from 0.92 to 1.2 They are fusible by a moderate heat, decomposed at a higher temperature, and in the open air take fire, burning with a yellow flame and much smoke. Insoluble in water, they are addition of water. With pure potassium and sodium hydroxides they unite to form soaps, which are soluble in water, and the same result takes place when they are heated with solutions of the alkaline carbonates. Concentrated sulphuric acid dissolves them with mostly soluble in ether and the volatile oils, and in alcohol; and their alcoholic and ethereal solutions afford precipitates upon the mutual decomposition, and nitric acid converts them into artificial tannin. They readily unite by fusion with wax and the fixed oils.
Losch recommends the following process for rendering the resins as white as possible. Boil together 5 parts of the resin, 1 of carbonate of potassium or of sodium, and 20 of water, until a perfectly homogeneous mass is obtained; allow this to cool, and pass into it sulphurous acid, which saturates the alkali, and precipitates the resin in white flakes. Finally, wash the precipitate well with water, and dry it. (J. P. C., June, 1856, p. 465.)