Chemistry of Essential Oils

LABIATE 235

had received only farmyard manure, and nearly treble that from land

which was not manured at all. It is interesting to note that the yield

from the natural unmanured marshy ground was the lowest calculated

on the amount of material employed, but was fairly good when referred

to the area of land concerned. The mint grown on a plot without any

manure and attacked by Puccinium gave oil containing the highest

percentage of esters, equivalent to 13*57 per cent, of menthyl acetate.

The same unaffected by the blight gave 10*73 per cent. The oil grown

on the natural unmanured marshy ground had the highest percentage of

total menthol, 64*25 per cent. The puccinium-attacked plant gave oil

containing 62*28 of total menthol, and coming next. The lowest menthol-

content, 57*69 per cent., was obtained from the plot manured with sodium

nitrate and superphosphate without any farmyard manure.

JAVAN PEPPERMINT OIL.

This oil is distilled from Mentha arvensis, var. Javanica. It has the

following characters:—l

Specific gravity at 15° C 0-9979 a

Rotatory power (I = 100 mm.) + 0° 24'

Soluble in 1J volumes of 70 per cent, alcohol, and the

solution remains clear on the subsequent addition

of the same alcohol.

Soluble in all proportions of 80 per cent, alcohol.

Esters, as menthyl acetate..17*5 per cent.

Combined menthol

Total menthol

Free „

Ketones and aldehydes.

13-8

48-2

34-4

none, or traces

BRITISH EAST AFRICAN PEPPERMINT OIL.

A sample of peppermint oil distilled from Mitcham plants grown at

Molo, in the highlands of British East Africa, has been examined

3

and

found to have an excellent aroma and a very high menthol value. It

had the following values :—

Specific gravity 0-967

Optical rotation - 33° 30'

Total menthol 67-5 per cent.

The most important determination to be made in the examination of

peppermint oil is that of the total menthol, but the menthone value is

also frequently required. This is best obtained by determining the total

menthol in the oil, and then reducing the menthone, *in a separate

portion, to menthol by means of sodium, and determining the menthol

in the reduced oil. If M 2 be the total menthol in the reduced oil and

Mx be that in the original oil the percentage of menthone present is

(M 2 - MJ154

156

The factor yf| representing the difference in the molecular weights of
menthone and menthol, may usually be neglected.
2 Peppermint oil is frequently adulterated. American oil is sometimes
1
2 Roure-Bertrand Fils, Bulletin,^3 (1910), 1, 59.
This is probably a misprint for 08979. A sample examined by Wielen had a
specific gravity 0921 and optical rotation + 4° 40'.
« P. and E.O.R. (1915), 4.