This section is from the book "A Treatise On Beverages or The Complete Practical Bottler", by Charles Herman Sulz. Also available from Amazon: A Treatise On Beverages.
The analyst will from the start labor under a decided disadvantage, since a prerequisite of any such examination is the behavior of a sample of undoubted purity; but owing to the fact that most, if not all, the oil of rose is tampered with, even by the producers themselves, it is next to impossible to obtain a perfectly pure oil. Coupled with this difficulty is another not less serious one, that the usual physical tests, solidifying point, melting point, specific gravity, etc., vary often quite considerably with the year of production and the locality.
Since most buyers put a strong but unjustified reliance on the solidifying test, it is to be presumed that a fraudulent addition of spermaceti has been made to an oil which has been largely adulterated with oil of rose-geranium, because the presence of the latter oil diminishes the solidifying tendency of the oil of rose. To detect this fraud, proceed as follows: Shake the oil to be tested with one and one-half to two times its bulk of liquefied glacial acetic acid; after a few minutes the mixture will form a crystalline mass, which is then transferred to a small filter, and washed repeatedly with glacial acetate acid, and lastly with water, till the odor has nearly disappeared; wash now with a little solution of carbonate of sodium, and finally with water. The insoluble mass which remains on the filter will be found to consist chiefly of spermaceti. In order to identify it, transfer the dry mass to a dry test-tube, and heat till it acquires a brownish color; an empyreumatic odor of burning fat shows spermaceti. This test can be checked by subjecting a small sample of spermaceti to the same treatment. It seems hard to believe that the stearopten of pure oil of rose should develop such an empyreumatic odor.
After Bauer: put in a test-glass one cm. of the rose oil to be tested, add five ccm. of alcohol of 75°, shake the mixture, then filter. The residue remaining on the filter is washed with a few drops alcohol, and dried between silk or blotting paper. Of this residue put a fraction on some paper, and warm cautiously. Pure camphor of rose oil evaporates entirely. If spermaceti, paraffine, etc., is present a distinct fatty spot remains.
Other tests are given as follows: Put one drop of the oil of rose into a dry test-tube, and add four drops of concentrated sulphuric acid. A perceptible rise of temperature takes place, and the mixture, which will assume a dark-yellow or dark-red yellow coloration, whether the oil is adulterated or not, must be allowed to stand until it becomes cool. Two grammes (thirty-one grains) of absolute alcohol are then to be added, and the mixture well shaken: When the oil is pure, the mixture of sulphuric acid, alcohol and oil will be clear and bright. When the oil has been mixed with geranium, pelargonium, or palm-rose oils, the solution will be turbid, and an insoluble precipitate will soon form. Pure rose-oil retains its characteristic odor when subjected to this test, but the mixture with these other oils evolves unpleasant odors (Hager).
The most certain criteria of the purity of the oil of rose are, according to Baur - 1, the odor, by which oil of rose-wood, sandal-wood, and others may be detected; 2, the temperature at which it congeals; and, 3, the manner of crystallizing. Pure oil of rose exposed to a temperature of 12.5° C. (54.5° F.) should congeal in a few minutes; the crystals should be transparent, scaly, iridescent, and float in the liquid, while spermaceti, being heavier, is deposited as a solid opaque crust. - N. D.
If a solution of one part of oil of rose in five parts of chloroform be diluted with twenty parts of alcohol, the mixture should separate crystalline scales, and should not redden moist litmus-paper. One drop of oil of rose, triturated with sugar and afterward agitated with 500 grammes of water, should impart to the latter the pure odor of rose. - P. G.
The vapors of nitrous acid, which are produced by putting in a watch glass some copper filings and pouring nitric acid upon them, placing all under a bell jar as in applying the iodine test, produces an apple-green color; if oil of rose-geranium be present, rose oil assumes a yellow color.
By the addition of some concentrated sulphuric acid the odor of the pure oil is not destroyed. If oil of rose-geranium is present, a disagreeable smell will appear. When but small traces of adulterations are present, these appearances take place sometimes after several hours.
See also Chapter XXIII (Syphons And Syphon Filling). on the general adulteration and tests of esser tial oils.