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.
On account of the marvelously low price of lemon oil, there seems to be but,very little inducement to adulteration, except by the mixing of the distilled with the expressed oil. Occasionally in years past, when oil of orange happened to be much lower in price than lemon, a mixture of the two was sent out into commerce. Just at present, however, the orange is more valuable than the lemon. Dealers have often been charged with the addition of turpentine to oil of lemon, but this is too clumsy a fraud. The terebinthinate (turpentine) odor of the suspected specimen was in all probability invariably due to the age and careless exposure of the oil, as described above.
Perhaps the most ingenious fraud in oil of lemon has been practiced by mixing it with an equal bulk each of absolute alcohol and castor oil. These could not, like turpentine or other low-priced essential oils, be detected by the odor and taste. Nor will they effect any serious change in the color, the liquidity or the specific gravity of the adulterated oil In some cases this mixture has even been put up in original copper cans, to which false seals of well-known Italian exporters have been affixed. To detect an adulteration with castor oil, alcohol, oil of turpentine, etc., apply the tests specified on page 639 and following pages.
There are several oils that by absorption of oxygen from the air will become camphorated, grow turbid, deposit a residue generally called stearopton, and lose more or less of their flavor, instead of which they acquire the odor of turpentine, and it becomes necessary to restore their fragrance. Those oils that are free from oxygen are chiefly subject to these changes, and it is therefore necessary to keep them in full bottles, well stoppered and in a cool place. When they have deteriorated in the way indicated they may be improved; but can never be restored to their original quality Many means have been proposed for this purpose, but the one now generally employed, is to shake the oil with about an equal volume of warm water several times, letting it settle, and drawing it off by means of a siphon or decanting. It may lastly be filtered through pape.
Another method is as follows: To each pound of rancid oil add about an ounce of the best glycerine, and .shake well together. In a few days the glycerine will have settled down to the bottom, carrying with it all the impurities, and leaving the oil above clear.
By treating the rectified spirit of turpentine in the following manner curious chemical changes take place: Spirit of turpentine, two quarts; rectified alcohol, three pints; nitric acid, ono pint. Agitate the mixture in a glass or earthen vessel, and allow it to rest. After one month the reaction will be complete, and a large quantity of hydrate of spirit of turpentine is obtained. This hydrate, mixed with alcohol, produces voluminous crystals. Submitted to the action of hydrochloric acid gas, the hydrate of turpentine loses a part of its water of crystallization, and is transformed into a hydrochlorate having all the properties of the camphor of lemon. When heated it loses part of its acid; then treated by potassium, it is transformed into a fluid, colorless oil, possessing the odor and chemical properties of the natural oil of lemon.