Chemistry of Essential Oils

MYETACBJE 337

If the oil be first diluted with petroleum ether, before treatment

with phosphoric acid, the results are rather more concordant in the

hands of different analysts.

Schimmel & Co. recommend the absorption of the cineol by a 40 to>

50 per cent, solution of resorcin in water, and reading the unabsorbed

portion in the neck of a Hirschsohn flask.

Ten c.c. of the oil containing cineol are mixed in a cassia flask of

100 c.c. capacity with so much 50 per cent, resorcinol solution that the

flask is filled for about four-fifths. The mixture is shaken thoroughly

for five minutes, and the oil portions which have not entered into reac-

tion are brought into the neck of the flask by adding resorcinol solution,,

and their volume determined. By subtracting the volume from 10 the

cineol-content of the oil is obtained, which is then expressed in per

cent, by volume by multiplication with 10.

Messrs. Schimmel & Co. have since modified the method by recom-

mending the oil to be first fractionated and the portion boiling between.

170° to 190° C. to be treated with the resorcin solution. In some cases

this gives results fairly concordant with those of the phosphoric acid^1

method usually adopted, as the following results will show:—

Cajuput Oil, normal.

„ ,, abnormal

Eucalyptus Oil I.

Cineol by Direct

Absorption with

Resorcin Solution.

62 per cent.

53

82

Cineol by Absorption

with Resorcin

after Fractionation.

54 per cent.

17

68 „

Cineol by

Phosphoric

Acid Process.

52 per cent.

1* ,.

65 „

C. T. Bennett

l

has, however, shown that this method is quite un-

reliable, only yielding accurate results in certain isolated cases.

In other cases, however, the results obtained are obviously too high.

An oil which yielded 95 per cent, distilling between 170* to 190° C.,

all of which was absorbed by resorcin solution, had the following char-

acters :—

Specific gravity ......

Optical rotation

Cineol by phosphoric acid method

,, by resorcin method

Other samples gave results as under :-

0-924

Nil

78 per cent.

95

Eucalyptus Oil A.

„ B.

„ C....

Cineol by

Direct

Absorption.

100 per cent.

Crystallised

»»

Cineol by

Absorption after

Fractionation.

89 per cent.

97

92

Cineol by

Phosphoric

Acid Process.

70 per cent.
75 „
73
1
It is evident that this modified method is not absolutely accurate
since other constituents, besides cineol, are undoubtedly included in the
portion boiling between 170° and 190° C. A further objection is the
separation of the solid crystalline double compound with oils rich in
cineol.

VOL. I.

. andE.O.E. (1912),^2
22