98 THE CHEMISTRY OF ESSENTIAL OILS
the natural violet flowers. Tiemann and Kruger then attempted to
synthesise irone, believing it to be the odorous principle of the violet
flower (of which so small a yield is obtained as to render an exact ex-
amination almost impossible). Whilst they did not succeed in produc-
ing irone, they obtained an isomeric body, pseudo-ionone, by condensing
citral with acetone, which on heating with dilute sulphuric acid is con-
verted into another isomer, which they termed ionone. This body is
the now well-known artificial violet perfume, so extensively used in the
so-called violet scent and soaps.
Schimmel & Co.
1
have isolated from the oil furfurol ; a terpene
which was not identified (specific gravity 0*861 ; rotation + 10° 40') ;
decyl aldeyde ; nonyl aldehyde ; naphthalene (a very rare constituent
of essential oils); and a ketone of the formula C 10 H 18 O. They do not
agree with Tiemann and Kruger that oleic aldehyde is present in the
oil.
Commercially, the aspect of orris oil is very important. Its unique
delicate odour will prevent it from being replaced by the more intense
but less delicate odour of ionone, and further, it forms an excellent
" fixer " for this artificial perfume, so that a judicious mixture of orris
oil and ionone leaves little to be desired. Its employment in fine per-
fumery is, and has been for many years, very extensive. A quite liquid
oil, from which the inodorous solid constituents have been removed, is
now on the market. According to Stead it has a specific gravity 0*949,
optical rotation - 28°, and congeals at - 5° C. Schimmel & Co., how-
ever, have shown that its characters are, normally, as follows:—
Specific gravity 0-930 to 0-940
Optical rotation.+ 14° „ + 30°
Refractive index at 20°...... 1-4950
Acid value 1 to 8
Ester „ 20 „ 40
It is soluble in from 1 to 1*5 volumes of 80 per cent, alcohol.ZINGIBERACE/E.
OIL OF GINGER.This oil is the product of distillation of the rhizome of Zingiber offi-
cinale, a native of tropical Asia, which is also cultivated in both East
and West Indies, and in Africa, and to a small extent in Australia.
Possibly, also, it is found in China, although the greater part of the
" Chinese ginger " appears to be the product of Alpinia Galanga.
The rhizomes are sometimes imported in the soft juicy condition
known as " green ginger," but the ordinary ginger of commerce consists
of the dried rhizomes which have been picked when the stalks have
withered, and are either washed, dried and scraped (uncoated or white
ginger), or merely washed and dried (coated ginger). Sometimes it is
bleached or limed before sale. The gingers of commerce are of widely
different value, according to their place of origin, and the aroma and
value of the oil naturally depend to some extent upon this. The
Jamaica product is most highly valued. The oil, which is obtained to
the extent of about 2 to 3 per cent., is a pale yellow to dark yellow
liquid of characteristic aromatic odour, but lacking the pungency of the
rhizome.
1
Report, April, 1907, 76.