This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol2", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
This is the substance left after the distillation of the volatile oil from turpentine. it is commonly called rosin in this country, and colophony in Europe. There are two varieties of it, one simply the residuum after the loss of the oil, the other the same incorporated with water during fusion. The former is sometimes distinguished as yellow resin or resina flava, the latter white resin, or resina alba. The yellow is more or less translucent, and varies, according to its purity, from a beautiful light amber colour almost to black; the white is opaque, and whitish or yellowish-white, owing to the mechanical intermingling of water. By time and exposure, the white resin gradually loses the water, and reverts to its original colour and translucency. So far as concerns our present purpose, it is sufficient to know, in regard to resin, that it has a feeble terebinthinate odour and taste, is insoluble in water, but soluble in alcohol, ether, volatile and fixed oils, and alkaline solutions,, softens with a moderate heat and then becomes adhesive, melts at 276o F., is decomposed at a red heat, and is inflammable. it readily unites with wax and fatty matter, when both are brought to the liquid state.
Resin is never used internally. Externally it is slightly irritant, and often excites inflammation in a very delicate skin. it is used exclusively in medicine as an ingredient of plasters, cerates, and ointments, in which it serves the three purposes of contributing to the preservation of the fatty matter, imparting adhesiveness, and rendering the preparation slightly irritant. it concerns us here simply as the chief constituent of the resin cerate.