"The best solvent for separating the r*>sin of Pipe gamboge is sulphuric ether. When agitated with the powder, a lively orange-red solution is obtained, which becomes Gamboge- yellow by dilution, and continues to show this tint when very greatly diluted, proving the exceeding intensity of the colour. On distilling off the greater part of the ether, and then driving away what remains by heating the residue in an open porcelain cup, a very beautiful, brittle resin is obtained, which has in thin layers a deep orange-colour and complete transparency, and in thicker masses a cherry-red tint, so dark as to produce almost complete opacity, and which possesses in fine powder a lively Gamboge-yellow hue.* It is remarkable that the very volatile fluid, sulphuric ether, adheres with great force to this resin, insomuch as to be the source of much trouble, and even error in a quantitative analysis. The vapour-bath heat of 212° F. 1 found insufficient to drive off so much ether as to leave the resin firm when cold ; even at the temperature of 270°, maintained by means of a muriate of lime-bath for six hours, so large a quantity was retained, that the detached principles almost always weighed conjunctly three per cent, more than the crude subject of analysis ; nay, a heat of 400° subsequently applied for four hours by an oil-bath, which I considered the highest temperature to be safely applied to the resin, and which sent off copious bubbles of ethereal vapour, still left a slight surplus of weight in the separated principles when summed up.
The ether leaves, in the case of Pipe gamboge, a flocculent matter, which, when thoroughly exhausted by the repeated action of the same fluid, coheres somewhat and acquires a very pale yellowish white colour. In fine specimens of this Gamboge I have always found the flocculent. residuum to be composed entirely of gum, presenting the leading characters of the prototype of the gummy principle named Arabin, from its forming almost the entire mass of gum arabic. It is entirely and easily soluble in cold water, forming a pale yellowish solution, which, when concentrated, becomes viscous, and when dried forms a transparent, reddish substance, of a mucilaginous taste without acridity. Braconnot thought the gum analogous to that of the plum-tree ; which, however, contains a considerable proportion of the insoluble variety of gum named Cerasin, a variety entirely absent in Pipe gamboge.
The proportions of the two principles vary somewhat, as will appear from the following results of trials made with one hundred grains of two distinct specimens apparently of the same quality.
First. Second.
Resin heated at 400°, till it ceased to lose weight 74.2 71.6
Arabin, or soluble gum, heated at 212°, till it ceased to lose weight 21.8 24.0
Moisture discharged by a heat of 270° 4.8 4.8
Woody fibre „ trace, trace.
Total 100.8 100.4
In another analysis so much as 27.3 per cent, of gum was obtained. But as the resin was not carefully determined, and there was therefore no check on the analysis, the accuracy of that result cannot be positively relied on.
It follows that Pipe gamboge consists of resin and gum, without any volatile oil, which is a very common ingredient of other gummy resinous exudations. The large proportion of gum accounts we'll for its easy miscibility with water, by which, on the one hand, its suitableness for the purposes of the painter is judged of, and which, on the other hand, renders it in medical practice convertible into a smooth and perfect emulsion, without any of the additions usually resorted to for that end."
" 2. — Passing next, to the lump or cake gamboge, it must appear evident, that the composition of this variety will vary much according to its quality,* * *" The chemical composition of Cake gamboge is also materially different. It is not, like the Pipe variety, entirely dissolved by the successive action of the two solvents, sulphuric ether and cold water. About eleven per cent of insoluble matter remains, which in cold water sub- sides commonly in two layers, the uppermost white, and very finely pulverulent, the lower one greyish, and rather flocculent. The former proved to be fecula, entirely soluble in boiling water, and then giving an abundant blue precipitate with tincture of iodine — the latter quite insoluble in boiling water, with even six hours of ebullition, burning entirely away, with the
- Its colour is so intense that it communicates an appreciable yellowness to ten thousand times its weight of spirit.
