LABIATE 245
No. 1 was distilled from English thyme grown from Sutton's seeds.
No. 2 was distilled from English thyme grown from young plants.
No. 3 was distilled from French thyme grown from seeds.
It will be seen from the above that the percentage of phenols is
highest in the case of the oil distilled from the plant grown from the
French seed, and the phenols partially crystallised. In the other cases
it is noteworthy that the phenols in the oils distilled from plants grown
from English seeds consisted chiefly of thymol, whilst the phenols of
the oil distilled from the English plants could not be induced to crys-
tallise, and therefore appear to consist chiefly of carvacrol.
The phenols are the principal constituents of thyme oil, thymol be-
ing the most valuable for medicinal purposes, but carvacrol, an isomeric
phenol, preponderating in some oils. Cymene and Z-a-pinene are pre-
sent in the oil, as well as a li tie menthone. Borneol and linalol have
been detected in the high boiling fractions of the oil, and a crysta line
body melting at 169° and having the formula C 10 H 2 2O 3. It is probably
identical with a similar body isolated from Juniper berry oil.
Admixture with the oil of Thymus serpyllum does not alter the
specific gravity, but increases the rotation, as this oil *rotates up to
- 12
°
. Oils adulterated with French turpentine have a high laevo-
rotation. A very large amount of the French " white" oil contains
a considerable quantity of turpentine. The percentage of phenols is
indicated by the decrease in volume on shaking with a 5 per cent,
aqueous solution of potash in a cassia oil flask, and also by the
amount of oil distilling above 220°, which should not fall below 25
per cent. Kremers recommends the following method of estimating the
thymol:—
Five c.c. of the oil to be examined is weighed and brought into a
glass-stoppered burette graduated to -^ c.c. and is diluted with about
an equal volume of petroleum ether ; a 5 per cent, potassium hydroxide
solution is added, and the mixture shaken for a short time, then the
liquid is left standing until separation is complete. Then the alkaline
solution is allowed to run into a 100 c.c. graduated flask. This opera-
tion is repeated until no further decrease in the volume of the oil takes
place.
The alkaline solution of thymol is made up to 100 or 200 c.c. as the
case may require, using a 5 per cent, soda solution. To 10 c.c. of this
solution in a graduated 500 c.c. flask is added a —$ normal iodine solu-
tion in slight excess, whereupon the thymol is precipitated as a dark
reddish-brown iodine compound. In order to ascertain whether a suf-
ficient quantity of iodine has been added, a few drops are transferred
into a test tube and a few drops of dilute hodrochloric acid are added.
When enough iodine is present, the brown cplour of the solution indi-
cates the presence of iodine, otherwise the liquid appears milky by the
separation of thymol. If an excess of iodine is present, the solution is
slightly acidified with dilute hydrochloric acid and diluted to 500 c.c.
From this 100 c.c. are filtered off, and the excess of iodine determined by
titration with ^ normal solution of sodium thiosulphate. For calcula-
tion, the number of cubic centimetres required is deducted from the
number of cubic centimetres of ^ normal iodine solution added and
the resultant figure multiplied by 5, which gives the number of cubic
oentimetres of iodine required by ihe thymol.
Every cubic centimetre of ^ normal iodine solution equals 0* 003753