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 following methods of detecting frauds are simple, reliable and easily executed, being selected from numerous proposals: Unsized paper is used to discover the mixture made with a fat oil; one or two drops of the oil examined are let fall on the surface of the paper, and then exposed to the air, or to a gentle heat. If the oil is pure, it is completely volatilized; if it is mixed with a fat oil, it leaves on the paper a permanent spot which renders it transparent. However, the appearance of a fat spot on the paper may in some instances be disappointing, as may be the case when resinified oils are under test, which leave on evaporation a somewhat transparent spot, without being adulterated by fixed oils. If resin is present the transparency will appear towards the edges of the evaporated oil drops. In doubtful cases it is best to evaporate some of the suspected oil on a watch glass over a sand bath. Fixed oil remains as a greasy mass if it was present in oil, while resin will congeal on becoming cool and be soluble in alcohol.
There is no reason to fear the adulteration of volatile oils by fixed oils, which are put in the still with plants at the time of their distillation for extracting the essence, because volatile oils begin to boil and are distilled at a temperature much below that which is required for the fixed oils.
Alcohol is also an excellent means for detecting this adulteration. It is sufficient, in applying this test, to place any quantity of the suspected oil in a graduated tube, and to pour on it eight times its bulk of pure alcohol and shake it. The alcohol dissolves the volatile oil, leaving the fixed oil, which falls to the bottom of the tube, where the quantity is indicated by the graduation. The old and unskillful methods of adulterating essential oils with oil of turpentine and purified benzine have almost disappeared, and in their place we have, as a chief adulterant, a solution of castor oil in alcohol, the density of the solution being made to conform as nearly as possible to that of the oil it is mixed with. This material possesses important advantages. It is colorless, almost free from flavor, and when such oils as peppermint, wintergreen, cinnamon, cloves, etc., are used in the preparation of essences, which, as is known, forms one of their chief uses, their solution in alcohol is prompt and satisfactory, without milkiness or other disturbance.
Fig. 418. - Graduated Tube.
It is quite common to meet with essential oils adulterated with this mixture, in proportions varying from twenty to fifty per cent If consumers of essential oils were fully alive to the importance of this subject, and would take the trouble to test the oils sent them, and promptly and invariably return all adulterated articles to the parties from whom they were purchased, this evil would soon be remedied.
To detect the castor oil, weigh accurately one hundred grains of the suspected oil in an ordinary watch glass, which has been previously tared. Place this in a sand bath, which may be roughly improvised by strewing a thick layer of sand over a piece of sheet iron placed on a stove. Heat the watch glass in this until all odor of the essential oil has disappeared, when the castor oil will be left unaltered, excepting, perhaps, a little discoloration from the heat to which it has been exposed, and may be easily recognized by its characteristic odor and taste. As soon as it has cooled, weigh the watch glass, with the remaining oil, when the weight in grains over and above the weight of the container will determine the percentage of the adulteration.
Draper's test for castor oil is the following: Evaporate twenty drops of the suspected oil as far as possible in a crucible, and add five to six drops of nitric acid. After the violent reaction that takes place is finished, add a solution of carbonate of sodium to neutralize. If castor oil was present the odor of oenanthic acid is perceptible.
To detect the alcohol mixed with the castor oil proceed after the following instructions: