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.

If accurate results are aimed at in the examination of an essential oil according to this table, the specific gravity should be determined by means of a scale sensitive to one one-thousandth gram, and the thermometer should be graduated to the tenth of a degree.

TABLE SHOWING THE APPROXIMATE DENSITY, BOILING AND CONGEALING POINTS OF THE MOST IMPORTANT ESSENTIAL OILS USED IN PERFUMERY.

—————————————————+—————————————+—————————-+————————————-+————————————— | | Boiling- | Congealing- | Essential Oil | Density. | Point, | Point, | Remarks. of | | Deg. C. | Deg. C. | —————————————————+—————————————+—————————-+————————————-+————————————— Absinth | 0·895 | ... | ... | Anise | 0·980 | ... | +10-15 | Bergamot | 0·850-0·890 | 188 | -24 | Bitter almond | 1·040 | 180 | ... | Do., art. | | | | (nitrobenzol) | 1·866 | 213 | +3 | Cajuput | 0·880 | ... | ... | Calamus | 0·962 | ... | ... | Camomile | 0·924 | 160-210 | ... | Camphor (Borneo) | ... | 212 | ... | Melts at 198 " (Chinese) | 0·985 | 205 | ... | Melts at 175 Caraway | 0·960 | 195 | ... | Cassia | 1·060 | 252-255 | ... | Cedar wood | ... | 264 | -22 | Cinnamon | 1·030-1·035 | 240 | below -25 | " leaf | 1·053 | ... | ... | Clove | 1·034-1·055 | 248 | below 20 | Forms | | | | crystals -16 Coriander | 0·871 | 150-200 | ... | Crispmint | 0·978 | ... | ... | Cubeb | 0·880 | ... | ... | Fennel | 0·960-0·980 | ... | +8 | Gaultheria | 1·173 | 224 | ... | Geranium | 0·895 | 216-220 | ... | Forms | | | | crystals -16 Hyssop | 0·889 | ... | ... | Juniper | 0·870 | ... | ... | Lavender | 0·870-0·940 | 186-192 | ... | Spike-lavender | ... | 140 | ... | Lemon | 0·850-0·870 | 177-250 | ... | " grass | 0·870-0·898 | 220 | -22 | Limetta | 0·931 | ... | ... | Mace | 0·890-0·950 | ... | ... | Marjoram | 0·890-0·920 | 163 | ... | Melissa | 0·855 | ... | ... | Neroli | 0·889-0·889 | 175 | ... | Forms | | | | crystals -16 Nutmeg | 0·880-0·948 | 172 | ... | " butter | ... | ... | 31 | Olibanum | ... | 162 | ... | Orange, bitter | 0·830-0·860 | 176 | ... | " sweet | 0·840-0·850 | 176 | ... | Parsley | 1·015 | ... | ... | Patchouly | 0·950-1·012 | 282-294 | ... | Peppermint | 0·902-0·930 | 188-212 | ... | Portugal | | | | (orange peel) | 0·840-0·850 | 176 | ... | Rose | 0·832 | 229 | +14-20 | Rosemary | 0·895-0·916 | 185 | ... | Rue | 0·911 | ... | ... | Sage | 0·902 | ... | ... | Santal | 0·950-0·980 | 288 | -22 | Sassafras | 1·082 | ... | ... | Serpyllum | 0·890-0·920 | ... | ... | Star-anise | 0·982 | ... | ... | Thyme | 0·870-0·940 | 170-180 | ... | Vanilla | ... | 150 | 76 | Vetiver | 1·007 | 286 | ... | Wintergreen | 1·180 | 220 | ... | Ylang-ylang | 0·980 | ... | ... | Turpentine | 0·855-0·870 | 160 | ... | Paraffin | 0·870 | ... | ... |Melts at 50-65 Wax | 0·960-0·970 | ... | ... |Melts at 65-70 Spermaceti | 0·943 | ... | ... |Melts at 45-50 —————————————————+—————————————+—————————-+————————————-+—————————————

In buying essential oils, except it be from a house whose reputation is a guaranty of their genuineness, it is to the interest of the perfumer to make a test. He must look for certain substances which are generally used for the sophistication of essential oils. These are: A. Other essential oils; B. Fixed oils; C. Alcohol; D. Paraffin, spermaceti, wax.

A. ADULTERATION OF ESSENTIAL OILS WITH OTHER ESSENTIAL OILS.

This mode of adulteration, which is frequent, is naturally the one most difficult of demonstration. In the case of cheap oils such as those of caraway, lemon, orange peel, etc., rectified oil of turpentine is almost without exception the adulterant. The methods usually recommended, such as attempting to dissolve out the oil of turpentine by strong alcohol, hoping thus to separate it from the essential oil, are without practical value.

The adulteration can, however, often be demonstrated by rubbing a drop of the suspected oil on a glass plate and testing the odor, provided the olfactory organ is trained. As the above table shows, the oils have different high boiling-points, while oil of turpentine boils at a rather low temperature, hence it evaporates sooner than the others and can be demonstrated by its odor.

The demonstration of an adulteration with an essential oil is most certain by so-called fractional distillation. Some of the oil to be examined (about four to six fluidrachms) is placed in a small retort with condenser and heated to a temperature a few degrees below the boiling-point of the oil in question. If, for instance, oil of bergamot adulterated with oil of turpentine is to be tested, it is heated carefully to nearly 188° C. (370° F.), the boiling-point of the oil of bergamot; the oil of turpentine which boils at 160° C. (320° F.) passes over completely, while the oil of bergamot remains in the retort.

Fractional distillation is also the most reliable way of demonstrating an adulteration with a fixed oil or with paraffin, wax, or spermaceti. An adulteration of oil of lavender with oil of spike-lavender, which is otherwise barely recognizable, is positively shown by this method; even oil of geranium in oil of rose, oil of cassia in oil of cinnamon, etc., may be thus demonstrated.

B. ADULTERATION OF ESSENTIAL OILS WITH FIXED OILS.

An addition of fixed oils can be easily demonstrated by agitation of the oil with strong alcohol in which the essential oil dissolves, while the fixed oil remains unchanged. Castor oil, however, is likewise soluble in alcohol and for this reason is frequently used for the adulteration of essential oils. Yet the presence of a fixed oil can also be shown in a very simple manner by placing a drop of the suspected oil upon white paper and leaving it for some hours in a warm spot. If the oil was pure, the translucent stain on the paper will disappear completely (also when the oil was adulterated with turpentine); but if it was mixed with a fixed oil, the stain will remain permanently and cannot be removed from the paper even by strong heat.

C. ADULTERATION WITH ALCOHOL.

This frequent adulteration is demonstrated either by fractional distillation, when the alcohol passes over first between 70° and 80° C. (158° and 176° F.), or by the use of the vessel illustrated in Fig. 31, which is divided into 100 equal parts.

The vessel is filled to the tenth division with the oil to be tested, and water is added to bring the volume to the 50 mark. If alcohol is present, it is taken up by the water so that the volume of oil appears to diminish. If the oil reaches to the mark 7, it contained three volumes of alcohol, or in other words it was mixed with thirty per cent of alcohol. It is true, essential oils likewise dissolve somewhat in water, but in such minute quantities as not to affect the success of the test.

D. ADULTERATION WITH PARAFFIN, SPERMACETI, OR WAX.

This mode of adulteration is practised mainly with viscid oils which congeal at rather high temperatures, such as oils of anise, rose, etc., the essential oils being usually mixed at the same time with oil of turpentine or paraffin. The fraud is easily detected by fractional distillation.

Oil of bitter almonds is often adulterated with oil of mirbane; this can be demonstrated by shaking 1 volume of the oil with 17 volumes of alcohol of 45%, and setting the mixture aside to settle. The nitrobenzol (oil of mirbane) will then collect at the bottom. Oil of Rose may be tested as follows: Mix the oil with an equal quantity of concentrated sulphuric acid. Neither the color nor the odor of the oil should be changed, but if oil of geranium was present a disagreeable odor and a darker color is produced.

It has been proposed, too, to test the oils by heating with iodine or nitric acid and determining the purity by the reaction; but the results with the different oils are so similar that the test is almost worthless. We have had the same experience with the test by nitro-prusside of copper which on being heated with essential oils gives colored precipitates differing with various oils, but still so similar that they cannot be relied upon. We have found in all cases that a comparison of an oil with a sample of known purity is the best, or else the tests given in the preceding pages.