ERICACEAE 279
gaultherine. The only physical difference between the two oils is that
of sweet birch quite inactive optically, both oils being almost pure methyl
salicylate C 6 H 4. OH. CO 2 CH 3. Cahours
l
was the earliest reliable in-
vestigator of wintergreen oil, but his work has been shown to be only
partially correct. According to him the oil consisted of about 90 per
cent, of methyl salicylate and 10 per cent, of a terpene, which he named
gaultheriline. Probably he examined an adulterated oil. Trimble and
Schroeter
2
stated that both oil o_LjEmtea?green and oil of birch contained
traces of benzoic acid and ethyl alcohol, together with"under 0*5 per
cent, of a hydrocarborf(different in the two oils). Power and Kleber,
3
however, have examined a very large number of samples, and give as
the result of their work the following summary:—
" Oil of Gaultheria.—Contains about 99 per cent, of methyl salicylate,
together with a small amount of a paraffin, probably triacontane C 30 H 62 ,
an aldehyde or ketone, an apparently secondary alcohol C 8 H 16 O, and an
ester C 14 H 24 O 2. To the latter body is possibly due the optical aclivity_
of the oil, whereas in the oil of birch it may be assumed that this body
has suffered inversion through the process of fermentation by which the
latter oil is formed.
" A pure fresh oil of gaultheria should show an optical rotation of
not less than - 0° 25' in a tube of 100 mm.
" Oil of Sweet Birch.—This oil consists to the extent of about 99
- 8
per cent, of methyl salicylate, and, in its unrectified state, contains also
a very small amount of the above-mentioned paraffin C 30 H 62 , and the
ester C 14 H 24 O 2 , but does not contain the alcohol C 8 H 16 O which is found
in gaultheria oil.
—" The oil of sweet birch is always optically inactive. —-
"Both of these oils have a specific gravity ranging usually from
1-180 to 1-187 at 15° C. Both of them, as well as the synthetic methyl
salicylate, form a perfectly clear solution with five (5) times their volume
of 70 per cent, alcohol at about 20° C., which, in connection with other
distinctive characters, is an excellent practical test for their purity.
" Neither the oil of gaultheria nor the oil of sweet birch contains any
trace of benzoic acid or its esters, nor does either of them contain any
terpene or sesquiterpene."
The above facts easily explain the appearance on the market of
artificial methyl salicylate, which is easily prepared by a condensation
of methyl alcohol and salicylic acid. It has been objected that the
odour of the artificial oil is not so fragrant as that of the natural oil,
but so long as the salicylic acid used in its manufacture is pure, no ex-
ception can be taken to it. As the synthetic oil is worth less than half
the value of the natural product of Betula lenta, and mixtures of the
two are impossible to detect, it is easy to understand how the producing
districts in America started importing the artificial oil, which returns to
commerce as natural oil. The purchase of this oil, so far as its origin
is concerned, must therefore be largely a matter of trust in the seller.
With the exception of the fact that the true oil of Gaultheria is faintly
laevo-rotary whilst the oil of Betula and the synthetic oil are optically
inactive, the limits as regards physical and chemical characters are
identical for the three oils. The specific gravity should never vary
outside the limits 1-180 to 1-193. The oil should give a clear solution
with five times its volume of 70 per cent, alcohol. On saponification
1
Annalen, lii. 331.
2
Jour. Amer. Chem. Soc. (1889), 398. - Pharm. Rundschau, 13 (1895), 228.