438 THE CHEMISTEY OF ESSENTIAL OILS
Lime " petit-grain " oil has the following characters :—
Specific gravity 0'875 to 0878
Optical rotation + 35° „ + 40°
Ester value 23 „ 28
An oil distilled from the unripe orange fruits, analogous to the old-
fashioned petit-grain oil, is manufactured and offered under the name of
" oil of orange peas ". Its specific gravity is about 852 to '854 and its
optical rotation + 75°. It is intermediate in composition between orange
oil and neroli oil. It contains methyl-anthranilate and also traces of
a pyrrol compound.
Umney and Bennett have examined a Buenos Ayres oil resembling
ordinary South American petit-grain oil, but having more free alcohols
and less esters than those oils. Pinene, dipentene, furfural, geraniol,
linalol, and geranyl acetate were found to be present. Its specific gravity
was 0*887, optical rotation + 2°, esters 36
- 5 per cent., and free alcohols
as geraniol 384 per cent.
Terpinyl acetate has been used recently as an adulterant of petit-
grain oil, and in 1912 a serious dispute took place as to the purity of a
sample suspected of containing this adulterant, several chemists holding
antagonistic opinions on the subjectr The sample was eventually re-
ferred to the author, and terpinyl acetate was found to be present, the
following method of investigation being adopted.
|The oil had the following characters :—
Specific gravity at 15'5° 08965
Optical rotation + 1° 10
i Refractive index at 20° 1-4650
Ester value (as ImaLyl acetate) 1 405 per cent.
The peculiar odour of the oil suggested the presence of an added
ester, the indication being that of terpinyl acetate.
The oil was examined, in the first place by means of a series of
fractional saponifications, and secondly by the fractional distillation of a
large quantity of the oil.
The three saponifications were carried out under identical conditions,
except that the times allowed for the reaction were 30 minutes, 75
minutes, and 120 minutes respectively. The results obtained were as
follows:—
S.V.
30 minutes' saponification. ........ 1157
75 „ 122-5
120 „ 124-8
The increase in values by prolonging the time of saponification is a
strong indication of terpinyl acetate, which is, as is well known, an ester
much more resistant to the action of alcoholic potash than linalyl acetate.
A much more marked indication is found by taking the differences in
the saponification values as suggested by Schimmel & Co. About 2 to 3
grams of the oil are saponified—(1) with 20 c.c. of semi-normal potash for
two hours; (2) the same amount of oil is used, but only 10 c.c. of semi-
normal potash, diluted with 25 c.c. of alcohol, and the saponification
allowed to proceed for one hour. Under these conditions Messrs.
Schimmel & Co. have shown that pure or nearly pure terpinyl acetate
will show a difference of practically 90 in the saponification value.
On the sample in question the following results were obtained :—