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.
Adulterating with alcohol alters volatile oils much less than the preceding. It has not, like the fixed oils, the objection of rendering them viscid; it renders them, on the contrary, more fluid, and does not change the color. The adulteration with alcohol is rendered certain when, on mixing the volatile oil with water, the mixture immediately becomes white and milky, as the alcohol unites with the water and the oil floats on its surface. The following method determines exactly the quantity of alcohol contained in a volatile oil: A graduated glass tube (Fig. 418) is filled with water to any height desired, and the same quantity of volatile oil is then added, a portion of the tube, at the top, being left empty. The two liquids are then frequently shaken, and after a moment's rest, if the oil contains alcohol, it will be observed that the volume of the water has increased, while that of the oil has diminished; the graduation on the tube will indicate the proportions of the mixture. The lighter oils, such as peppermint, will float on the surface of the water, while heavy oils, such as wintergreen, will be underneath. Glycerine can be used in place of water. If olive oil is used instead of water, the alcohol, unless present in a very small quantity, will separate.
Potassa has the property of promptly demonstrating the presence of alcohol in volatile oils. The following is the process by which the car-bonator may apply this reagent successfully. It consists in putting a bit of dry potassa, as large as a pin-head, into a small quantity of the suspected volatile oil. It is soon covered with a yellowish film when alcohol is present. If the oil contains so much as one-fourth of alcohol at 90° or 60°, the potassium at once assumes a round form, with a brilliant and shining aspect like a globule of mercury; it moves about, oxidizes very promptly, and disappears in at least one or two minutes; a slight noise always accompanies these phenomena. When the alcohol is only mixed in the proportion of a sixth, an eighth, a twelfth, and even a twentieth, the same phenomena take place; it is only to be observed that the potassium disappears more slowly, and the noise is much less sensible when the proportion of alcohol is less considerable.
Aniline-red is soluble in alcohol and insoluble in volatile oils; but if the oils contain alcohol, they are colored red by the dry aniline color.
A method proposed for detecting alcohol in essential oils is a combination of the distillation and the fuchsin process, which is claimed to be the most sensitive, is as follows: A little of the essential oil is poured into dry test tube, taking care not to wet it in its upper portion, and a few fragments of fuchsin (analine-red) are then sprinkled upon the middle and upper inside surface of the test tube. On heating, no change will be observed, if alcohol was absent. But if the oil contained even as little as one-tenth of one per cent, of alcohol, the ascending vapor of the latter will cause each particle of fuchsin to be surrounded by a red stain, either at once or after setting the test tube aside for a short time. It is easy to recognize by this test the presence of one milligramme of alcohol in one gramme of the oil. This test is applied specifically to oil of lemon, but the method will undoubtedly be applicable to other essential oils, or to the detection of alcohol in other liquids which do not of themselves exert any solvent action upon fuchsin. Another chemist who has tried the process upon a few other oils, found it to work satisfactorily. He recommends to put a small quantity of essential oil into a long test tube without wetting the sides, then to push a loose pellet of cotton down 41 to the middle of the test tube, and to sprinkle a very little powdered fuchsin in. The boiling must be done cautiously.