because it must be called an important substance to know for the perfumer, inasmuch as it is very frequently used for the adulteration of different essential oils. Oil of turpentine, which is obtained from incisions into the bark of different fir and pine trees, the exuding resin being distilled with water, comes into commerce from various sources. Different sorts are distinguished, but to the perfumer only the rectified oil of turpentine, oleum terebinthinæ rectificatum, is important. Oil of turpentine has a yellowish color and a decidedly disagreeable, resinous, and burnt taste. By repeated distillation, especially over quicklime or chloride of lime (bleaching powder), it is finally obtained as a colorless, very refractive liquid with a density of 0·855 to 0·870 and a boiling-point at 160° C. (320° F.). Its odor is peculiar, but not easily distinguished from that of old essential oils, such as oils of caraway, anise, etc. One peculiarity of oil of turpentine is that its odor is easily masked by that of other essential oils, so that, for instance, a comparatively large quantity of oil of turpentine needs the addition of but little oil of anise to impart to the entire mixture a rather pronounced odor of anise. This peculiarity has led to the frequent employment of rectified oil of turpentine for the adulteration of other essential oils.
[CHAPTER IX.]
THE ADULTERATIONS OF ESSENTIAL OILS AND THEIR RECOGNITION.
We find it necessary to devote a special chapter to the adulterations of the commercial essential oils because an experience of many years has shown us that hardly any other group of products is subject to so many sophistications as essential oils. The high price of most aromatic substances and the difficulty of recognizing the adulteration furnish an inviting field to the unscrupulous manufacturer. In the best interest of the perfumer, therefore, we advise the purchase of essential oils only from renowned reliable houses, even at higher prices, for the cheap commercial products are almost worthless, since they are almost without exception adulterated.
The adulterations are very manifold. Some expensive oils are mixed with cheaper ones having a similar odor—for instance, oil of rose with oil of geranium or oil of geranium grass; oil of orange flowers with the oil from Philadelphus coronarius; oil of verbena with oil of lemon grass; oils of caraway, anise, and fennel with oil of turpentine; oil of cinnamon with oil of cassia, etc. Besides these, other deceptions are practised—for instance, oil of anise is mixed with oil of turpentine and in order to make the mixture congeal readily (which is the characteristic of true oil of anise, as above stated) paraffin or spermaceti is added. A similar practice prevails with adulterated oil of rose and other viscid oils. Oil of bitter almond we have found adulterated with or entirely replaced by nitrobenzol, etc.
The demonstration of the adulteration of an essential oil by chemical means offers many difficulties. We devote particular attention to the physical characteristics, for experience has shown us that the olfactory organ—provided it is very expert—is often able to determine the genuineness of any aromatic substance when other tests have given only uncertain results, or can give certain results only in the hands of experts. To make this test, however, quite reliable, it is necessary to be familiar with the substances in their pure unadulterated condition.
The manufacturer of perfumery, therefore, should spare neither trouble nor pecuniary sacrifices to obtain possession of absolutely genuine specimens of those essential oils, even in minute quantities, which he intends to employ. Such samples should be carefully preserved (protected from heat, evaporation, daylight, etc.) for the purpose of immediate comparison with the oils to be purchased.
As above stated, the physical properties of the essential oils usually furnish the means of recognizing their purity, and these give more reliable results to the practical perfumer than the chemical tests. The most valuable points are furnished by the boiling-point, the congealing-point, and the density of the oils. The following table gives the boiling and congealing points of the most important essential oils in degrees of the centigrade thermometer, together with the density (or specific gravity); where two figures are given, they indicate the extreme limits found in genuine samples.
Special characteristics of some essential oils with reference to their action at low temperatures or their melting-point are given in the column “Remarks.”
Oil of turpentine, paraffin, wax, and spermaceti being frequently used for the adulteration of essential oils, have been included in the table.