EUTACE^E 419
During the latter part of June and the month of July in some seasons,
a number of samples of undoubted authenticity have been examined and
found to have an abnormally low optical rotation sometimes as low as
+ 51°. In some cases the odour of the lemon oil is quite abnormal, and
gives one the impression that it had been contaminated with neroli oil.
The reason of this appears to be that the spring lemons (" bianchetti"),
which are rarely used for pressing for oil, as the oil is inferior and the
yield small, are in such seasons being pressed in large quantities; and
where this neroli odour is found, it is probable that some quite immature
fruits have been used for pressing.
If pure lemon oil be carefully distilled from a three-bulbed fractionat-
ing flask, and the first 10 per cent, collected, its optical rotation will
rarely differ from that of the original oil by more than 5°, or at most 6°,
the rotation of the fraction being lower than that of the oil. The size of
the flask and the rate of distillation cause considerable variation in this
figure, so that unless a marked difference is found, such as would result
from adulteration with an appreciable quantity of turpentine, too much
stress must not be laid upon the result of a test which, after all, is em-
pirical in its nature.
Adulteration, which was until recently very frequent, is still common.
Turpentine was the regular adulterant, with, at times, the poorer quality
distilled oil of lemons. But adulteration with turpentine is now so easily
detected that the sophistication is frequently carried out in a more scien-
tific manner. Mixtures with the proper specific gravity and optical rota-
tion can easily be made up from turpentine and orange oil—the poorer
qualities of the latter of course being used—and such mixtures are often
used to adulterate the oil. But the most formidable adulterant from the
analyst's point of view is one that has only come into vogue during the
last few years, viz. the terpenes obtained in manufacturing the " terpene-
less " or concentrated oils of lemon and oil of orange, the latter being
sometimes added to turpentine to raise the optical rotation.
The terpenes are sometimes used alone, sometimes together with a
little citral obtained from lemon-grass oil. It is a common custom to
export oil of lemons with a guaranteed citral-content, and to sell it upon
that basis. In judging of the value of such a basis for the market value
of the oil, the following points should be noted :—
- The value of the oil depends on its percentage of all the oxygenated
constituents, which are soluble in weak alcohol.
- The terpenes are practically odourless and insoluble, therefore
valueless for the general purposes for which lemon oil is employed.
- The percentage of terpeneless oil obtained by careful fractionation
is an indication of the value of the oil.
Some samples of lemon oil produced in Spain have recently been
examined, and, as instancing the differences between oils manufactured
in different districts, have the following characters which would be con-
sidered impossible in the case of pure Sicilian oils :—
Specific gravity 0'853 to 0-862
Optical rotation + 63° 82' „ + 65° 30'
Refractive index 1-4737 „ 1-4738
Citral 3-1 to 3-2 per cent.
The optical rotation of the first 10 per cent, distilled was found to be
-about 3° higher than that of the original oil.
The most important method of analysis applicable to lemon oil is the
