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.
[Illustration: FIG. 31.]
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.