Chemistry of Essential Oils

244 THE CHEMISTBY OF ESSENTIAL OILS

OIL OF THYME.
French oil of thyme, which is the most esteeme 1 variety of the oil
known, is distilled from the fresh herb, Thymus vulgaris. A consider-
able quantity of thyme oil is also distilled in Spain, but probably from
mixed species of thyme, and a certain amount is also distilled in Al-
geria from Thymus algeriensis.
Two commercial varieties are recognised, the " red" and " white "
oils. The former is the crude distillate, and probably owes its red
colour to the action of the phenols present on the iron of the crude
stills and condensers frequently used. The red oil when properly
rectified forms the colourless or "white" oil of commerce. The yield
of oil is very variable—sometimes being as low as 0*2 per cent., often
rising to 1 per cent, in the fresh and 2-5 per cent, in the dried herb.
The French oil contains from 20 to 35 per cent, of phenols, chiefly thy-
mjl, upon which the value of the oil chiefly depends. The Spanish oil
contains a much higher percentage of phenols (50 to 70 per cent.) of
varying composition. A few years ago carvacrol was generally the pre-
ponderating phenol, but to-day careful selection of the species or varieties
distilled has enabled a Spanish oil to be produced, so rich in thymol that
this body is actually manufactured from it.
E. M. Holmes has recently shown that there are two Spanish species
of thyme now known to yield thymol as the principal phenol. These,
are Thymus vulgaris and Thymus Zygis.
1
French oil of thyme has the following characters:—
Specific gravity.. 0-905 to 0'935 (rarely 0'900)
Optical rotation.. - 0° 30' to - 4°
R .-fract.ve index.. 1-430J „ 1'4'J50
Phenols (mostly thymol) 20 to 40 per cent, (rarely below 25 per cent.)
The oil is soluble in 2 volumes of 80 per cent, alcohol.
Spanish thyme oil has the following characters :—
Specific gravity ' 0'928 to 0'958
Optical rotation + 2° „ - 4
°
Refractive index 1-5025 ., 1-5110
Phenols...50 to 75 per cent.
It is soluble in 3 volumes of 70 per cent, alcohol. The phenols of
Spanish thyme oil consist principally of carvacrol, but sometimes a.
fairly large proportion of tnymol is present.
J. C. Umney^2 has examined three samples of thyme oil distilled hi
British East Africa.
The three samples of thyme oil were distilled respectively from
plants grown from seeds obtained through Sutton & Co., of Beading,
from young plants from the same source, and from French seeds of
Thymus vulgaris. The following are the characters of the oils :—

No. Yield.

Per Cent.

0-50

0'70

0-38

Specific

Gravity.

0-901

0-905

0-905

Phenols.

Per Cent.

32

32

40

Refractive

Index.

1-4900

1-4768

1-4908

Remarks.

Phenols solidify.

,, liquid.

„ partly crystallise.

. cmd E.O.R. (1920), 339.^2 Ibid. (1914), 423.