246 THE CHEMISTKY OF ESSENTIAL OILS
grm. of thymol. Knowing the quantity of thymol in the alkaline solu-
tion, the percentage in the original oil is readily found.
The reaction taking place is represented by the equation :—
CioHi4° + 41 + 2NaOH = C 10 H 12 I 2 O + 2NaI + 2H 2 O.
In the estimation of carvacrol a slight modification of this'method
must be made, because carvacrol is thrown down as a finely divided
white precipitate, giving the solution a milky appearance. In order to
form a precipitate the liquid is vigorously shaken after the addition of
iodine solution, and is subsequently filtered. Then the liquid is acidu-
lated with hydrochloric acid, and subsequently the same procedure is
followed as was described for thymol. The calculation is also the same.
Labbe^1 has examined an authentic sample of thyme oil and found it
to contain 30 per cent, of thymol, 17 per cent, of a terpene which he
could not identify, 15 per cent, of menthene, 21 per cent, of cymene,
5 per cent, of linalol, 8 per cent, of borneol, and traces of carvacrol.
Thymus capitatus also yields an oil of specific gravity about *900,
and closely resembling the above-described oils. It contains pinene,
cymene, dipentene, thymol, carvacrol, and bornyl acetate. Its phenol-
content is about 6 per cent. A similar oil is obtained from Thymus
camphoratus. A somewhat different oil is obtained from a variety of
Thymus serpyllum (citratus or citriodorus). This oil has an odour re-
calling thyme, lemon, and geranium. Its specific gravity is 0
- 890 to
0920 and its optical rotation - 10° to - 20°. It contains only a very
small amount of phenols, but cymene and a sesquiterpene have been
isolated from it.
The value of this oil depends so much upon the phenols it contains
that it is important that these should be estimated, as the abstraction of
thymol, a valuable commercial product, is by no means uncommon.
Thymus Mastichina, the so-called Spanish wood marjoram, yields an
oil of thyme which has been examined recently by Dorronsoro.
2
It
has a bright yellow colour, turning darker with age, and a camphorace-
20°
ous odour reminding of thyme. Its constants are as follows : d^o 0907
to 0945; CID - 0° 50' to + 4° 40'; n^ 0 14630 to 14654; saponifica-
tion value 127 to 185 ; ester-content 444 to 6-47 per cent, (calculated
as linalyl acetate); ester value after acetylation 29*2 to 49
- 3 = 8
2 to
14*09 per cent, alcohol C 10 H 18 O.
The oil is soluble in any proportion in 94 per cent., in one-half to its
own volume in 90 per cent., and in 1 to 3 volumes of 80 per cent,
alcohol. It does not always dissolve readily in 70 per cent, alcohol, 30
volumes of this strength being occasionally required to make a solution.
The oil was split up into 8 fractions by distillation under reduced
pressure.
Temperature (98 to ICO mm). Per Cent.
Up to 100° 2-65
100° 1
110° 1
120° 1
125° 1
145° 1
160° 1, 110°
, 120°
, 125
, 145°
, 160°
, 175°
43*00
28-53
6-25
10-25
3-75
3-05
»D» 2 °-
1-4600
1-4620
1-4605
1-4617
1-4657
1-4718
1-4781
+ 3° 41
+ 4
°
+ 1°58
±0°- 3°
- 4° 10
- 1°55
a Soc. Chim. iii. 19, 1009.
Paper read before the Soc. Espan. Fisic. y Quimica, October, 1910.