Chemistry of Essential Oils

EUTACE^ 449

in many cases not absolutely essential, is desirable on account of the fact
that sulphuric acid is liable to become reduced by certain constituents of
oils, particularly of old oils, which frequently contain substances of a
resinous nature. In such cases the v latile acid products of the reduc-
tion pass over along with the true acids of the oil undergoing examina-
tion.
The relations which the abnormal results obtained bear to the above
outlined conditions are clearly shown by the appended figures :—

Method.

1. Oil saponified by solution of potash in unpurified methy-
   lated spirit. Excess of alkali neutralised by hydro
   chloric acid and the acids liberated, previous to dis-
   tillation by sulphuric acid


2. As 1, but the excess of alkali after saponification neutra-
   lised by sulphuric acid


3. As 2, but the methylated alcoholic potash replaced by a
   solution of potash in 96 per cent. (60 o.p.) alcohol


4. As 2, methylated alcoholic potash (the spirit being
   previously purified by distillation over potash) being
   used instead of the solution of potash in unpurified
   spirit


5. As 2, the methylated alcoholic potash being replaced by
   a solution of potash in absolute alcohol purified by
   distillation over potash .......
   (>. A " blank " experiment, employing for distillation the
   residue resulting from the evaporation of 25 c.c. of the
   alcoholic potash used in 5, previously neutralised by
   means of sulphuric acid .......


6. Ester found in 5 less the amount of ester equivalent to
   the volume of deci-normal sodium hydroxide used up in
   the blank experiment .......

Percentage of Ester

found.

47-28

43-51

41-38

41-45

41-00

1 -5 c.c. deci-normal

sodium hydroxide

was required for

the neutralisation

of the distillate

39 69

It is evident that, in order to obtain accurate results, the method of
working must be clearly and minutely adhered to, especially in view
of the fact that the determination of ester by the method of steam distilla-
tion is a very valuable indication as to the purity of an oil, serving to
detect the fraudulent addition to oils of such esters as diethyl succinate,
triethyl citrate, and diethyl oxalate, the free acids of which are non-
volatile in steam. It will not detect glyceryl acetate or terpinyl acetate.
The method, yielding reliable results and including modifications, devised
to remove the sources,of error above-mentioned, is as follows:—
About 2 grams of the oil (bergamot or lavender) is accurately weighed
into a carbon dioxide flask, and 15 c.c. neutralised alcohol added along
with a few drops of phenolphthalein solution, and the whole is just
boiled on the steam-bath. The acid number is ascertained by titra.ion
with deci-nor ral alcoholic potassium hydroxide, 25 c.c. semi-normal alco-
holic potash (made with 90 to 96 per cent, spirit, preferably distilled over
potash) is now added, and the whole boiled under a reflux condenser for
one hour, the excess of potash, after saponification and addition of 40 c.c.
VOL. i. 29