7. (Dr Hager.) Copaiba which is adulterated with Gurgun balsam is not quite clear, and frequently exhibits prisms of gurginic acid under the microscope. The author states that the adulteration may be easily detected by mixing the suspected sample with four volumes of petroleum ether; the mixture at once becomes turbid, and gradually deposits a sediment, which, after half an hour’s settling, occupies the same volume as the copaiba operated upon. A mixture of pure copaiba with petroleum ether is clear at first, and either remains clear upon standing or it deposits after several hours a very slight sediment, which merely covers the bottom of the test tube like a thin film. Benzol may be used in place of petroleum ether.
8. (Muter.) Three to four grams of the sample are weighed into a clean, dry flask, and saponified on the water bath with 50 c. c. of alcohol, and a lump of caustic soda weighing not less than 5 grams. When all is dissolved water is added, and the whole washed into a half-pint basin, so as to nearly fill it, and evaporated to 100 c. c. over a low gas flame. Dilute sulphuric acid is then added till the whole just becomes permanently turbid, and then solution of caustic soda is dropped in till it just clears again. By this means a solution is obtained with the least possible excess of alkali, and with a good amount of sodium sulphate. The whole is now to be evaporated to perfect dryness on the water bath, stirring towards the end, so that the sulphate may mix with the soaps, and produce an easy pulverulent residue. The residue is moved from the basin into a small, wide-mouthed, stoppered bottle, treated with 70 c. c. of ether-alcohol, and well shaken up. As soon as it is fairly settled the fluid is filtered off through a quick filter, and this is repeated with two successive quantities of 70 c. c., making 210 c. c. in all of the solvent used. The residue in the bottle and in the filter now consists of sodium oleate and sulphate if the balsam be impure, and of the latter only if pure, with a little trace of the insoluble resin soap already referred to. The contents of the bottle and filter are then dissolved in warm water, and after heating until all smell of ether is gone the whole is boiled freely acidulated with hydrochloric acid, and set to cool.
If, when cold, nothing but a few specks of brown resin should rise to the surface, the balsam is pure; but if an oily layer be formed it is adulterated, and the smell of the separated oleic acid will at once determine whether it is actually castor oil or not.
In the case of the presence of oil, 2 grams of pure and dry white wax are added, and the whole heated till the wax melts with the oleic acid. On cooling, a solid cake is formed, which is detached from the side of the beaker, and the fluid below passed through a filter. The cake is once more melted in boiling water, cooled, detached, dried by gentle pressure between blotting paper, dried in a water-oven in a weighed platinum dish, and then weighed, and the weight of the wax used deducted. The beaker, filter, rod, &c., used are, if at all dirty, dried, extracted with ether, and the residue left, after evaporation, weighed and added to the total.
The calculation is then performed as follows:—
(1.) To the weight in grams found add ·20 for loss of oleic acid in solvent, and then say as 95 : 100 :: total oleic acid.
(2.) Calculate the per-centage from the quantity taken, and from this deduct 6 per cent. for possible altered resin in the balsam. The error, owing to the correction, of course, increases with the amount of oil present; but it is stated to be always an error in the direction of under-estimation, which is the great point for public analysts. When working on 3 to 4 grains with an admixture of not over 25 per cent. the errors due to loss of oleic acid and insoluble resin soap are said to so nearly balance each other, that any correction is unnecessary, and the actual amount of oleic acid found may be taken as correct within a per cent.
9. (B. P.) According to the British Pharmacopœia, copaiba should be soluble in an equal bulk of benzol.
10. (The evaporation test.) Mr Siebold says: “This is an excellent and exceedingly simple test, but is clumsily applied by many. Instead of boiling the balsam with water for many hours, a small quantity (about 1 to 1·5 gram) of the sample should be carefully heated in a watch-glass until all the oil is driven off, which is the case as soon as the residue has assumed a rich brown colour. A few minutes suffice for the experiment.
“If the remaining resin is perfectly brittle and pulverisable there is no fatty matter present, for 1 per cent. of oil would diminish the brittleness of the resin, so that it cannot be reduced to a fine powder. One per cent. of oil is thus readily detected, and with larger quantities of the adulterant (3 to 5 per cent.) the resin feels quite sticky.