Oil of Citronella.
Related entry: Oil of Lemon Grass
Oil of Citronella.—There are a group of closely allied grasses which yield sweet scented volatile oils. Of these volatile oils, which are sometimes spoken of collectively as Indian Grass Oils, there are at least five commercial varieties, namely, Oils of Citronella, Lemon Grass, Palmarosa, Ginger Grass, and of Vetiver. The botany of the sweet-scented grasses from which perfumery oils are obtained, has been somewhat confused. Stapf (see Schim. Rep., April, 1907, p. 20) divides them into three groups, the Cymbopogon, Andropogon and Vetiveria.
Andropogon nardus L. (Fam. Gramineae) yields citronella oil. It grows in Ceylon, the Malaccan Peninsula, India and to some extent in tropical East Africa. There are two principal varieties, the one, Lana Batu, grows widely in Ceylon and yields an oil relatively poor in geraniol and is the principal source of the oil of commerce. The second variety, known as Matia pangiri, is generally cultivated in the Straits Settlements and in Java. This latter oil has a lower specific gravity, a lighter color and is claimed to be superior in quality.
Oil of citronella is produced in Ceylon, the Straits Settlements, close to Malabar, the Malay Peninsula and Java, the last named being the most highly esteemed. The exports of citronella oil from Ceylon amounted in the year 1909 to 1,512,084 pounds. Oil of citronella is of a yellowish-green color, having a characteristic odor and pungent taste. Its sp. gr. is, according to Gildemeister and Hoffmann, 0.886-0.900. It mixes with alcohol in all proportions, and the test for purity given by Schimmel and Co. is based upon its behavior towards alcohol of 80 per cent: "One volume of the oil must form an absolutely clear solution with two, or at least two and a half, volumes of 80 per cent. alcohol at a temperature not below 20° C. (68° F.). A cloudy mixture indicates the presence of turpentine, certain fixed oils, and other essential oils which are sometimes used to adulterate it." The most important ingredients in this oil are geraniol and citronellal which together may make up as much as 93 per cent. of the oil. It is not used in medicine, but is largely used in the arts, for perfuming cheap soaps, especially so-called honey soap. An ointment containing 25 per cent. of the oil of citronella affords an excellent protection against the bites of mosquitoes and other insects.
Oil of lemon grass is official in the British. Pharmacopoeia (1914). (See Oleum Graminis Citrati.)
The Palmarosa oil is produced chiefly in India, and is the product of the Cymbopogon martini (Andropogon schoenanthus Pluck. and Hanb. not L.). Its most important ingredient is geraniol, of which it may contain as high as 94 per cent. It is largely employed in the perfumery arts, and also as an adulterant to the oil of rose and the oil of geranium.
Ginger grass oil resembles palmarosa oil in its properties but contains a much smaller percentage of geraniol.
From the roots of the vetiver or cus-cus grass, Vetiveria zizanoides Stapf. (A. muraticus Retz), which grows in the island of Reunion and in the Philippine Islands, is distilled a volatile oil. The odoriferous principle of this oil is at present unsettled. It has been attributed by Genivesse and Landlois to a peculiar alcohol which they named vetivenol, but this has been denied by Bacon. (Philippine Journal of Science, 1909, iv, p. 118.)
Various other allied grasses, such as the Cymbopogon polyneuros or Delft Grass, and the C. Coloratus, etc., yield sweet-scented oils which have, however, not become commercially important.