Citron oil is frequently adulterated with oil of orange and sometimes with oil of bergamot. These adulterations are readily detected by an experienced person by the odor, this being in fact the best guide. The specific gravity of citron oil is 0.850 at 59° F.; it boils at from 332.6° to 343.4° F. and congeals at 4° F.
Citronella oil (oleum citronellæ) is chiefly distilled in Ceylon from the lemon grass, Andropogon Nardus, L. It is quite limpid, of a greenish-yellow to brown color, and has an odor resembling that of genuine citron oil. Its specific gravity is 0.896 at 59° F., and it boils at from 392° to 410° F. Of the various oils reaching the market that with the trade-mark "Fisher" is most in demand, it being distinguished by special purity. Edward Kremers has found in citronella oil an aldehyde, C7H14O, a terpene, C10H16, citronellol, which is isomeric with borneol; further, acetic acid and valerianic acid.
The Indian distillers, it is claimed, adulterate the citronella oil with petroleum, an addition up to 25 per cent. being not uncommon.
According to experiments by Schimmel & Co., pure citronella oil must give a clear solution, when 1 part of the oil is vigorously shaken with 10 parts of 80 per cent. alcohol. If, in executing the test, the kind of turbidity is observed, and whether the portion insoluble in alcohol separates, after standing, upon the surface or on the bottom of the fluid, and further, if the above-mentioned quantity of alcohol is not added at one time, but at first only 1 or 2 parts of it, a conclusion may be drawn as to the kind and quantity of the adulterant.
Petroleum causes a milky-white turbidity, while in the presence of fat oil the mixture becomes turbid, but not actually milky. As a rule, fat oil deposits, after standing, on the bottom, while petroleum floats upon the surface of the fluid. Citronella oil adulterated with fat oil does not dissolve in 1 to 2 parts nor in 10 parts of 80 per cent. alcohol, while oil adulterated with not too large a quantity of petroleum, gives a clear solution with 1 to 2 parts. The determination of the specific gravity may also serve for the detection of adulterations. This holds good, however, only for petroleum, which reduces the specific gravity, an addition of fat oil producing no deviation in this respect. The specific gravity of the oil should not be below 0.895 at 59° F.
Citronella oil is much used for perfuming cheap hair oils and toilet soaps; it is the chief constituent of all perfumes for honey-soaps. In the American soap industry it is extensively used, the yearly consumption being estimated at 1½ million ounces.
Cloves, oil of (oleum caryophylli), is obtained by distillation with steam, or by extraction from the cloves of commerce, which are the dried unexpanded flower buds of Caryophyllus aromaticus, L., or the clove tree. Oil of cloves, when fresh, is almost colorless, but on exposure to air acquires a brownish coloration and a thickly fluid consistency. It has the aromatic taste and odor of cloves, and a specific gravity of 1.300 to 1.065. It frequently shows a slightly acid reaction, boils at 482° F., and congeals at 4° F. It is readily soluble in alcohol, ether, and strong acetic acid. It consists of a terpene (C10H16) and eugenol (C10H12O2), the odor of the oil being due to the latter. The terpene has a specific gravity of 0.918, and in distilling passes over first (light oil of cloves). The eugenol, when fresh, is colorless, has the odor and taste of cloves, a specific gravity of 1.063 at 65° F., boils at 487.4° F., is insoluble in water and glycerin, but soluble in alcohol, ether and glacial acetic acid. Its alcoholic solution is colored magnificently blue by ferric chloride. If in an alkaline solution it is oxidized with potassium permanganate, vanillin being formed.
An inferior quality of oil is obtained from the stems of the clove buds. It dissolves with greater difficulty than the oil prepared from the buds, and has a darker red-brown color.
To test the value of oil of cloves, introduce, according to Stohman, into a graduated glass cylinder 10 volumes ether, 10 oil of cloves, and 30 of a 10-per cent. soda solution. After vigorous shaking, the eugenol dissolves; the increase in volume of the aqueous fluid is then proportional to the quantity of eugenol present. For more exact determinations, dissolve a weighed quantity of oil, repeatedly shake the aqueous fluid with ether to remove the terpene, then decompose the eugenol-sodium with dilute sulphuric acid, dissolve the separated eugenol in ether and weigh after evaporating the ethereal fluid. Good oil of cloves does not contain less than 80 per cent. of eugenol, and frequently 90 per cent. or more.
Oil of cloves is chiefly adulterated with copaiba oil and cedar oil. Such adulteration is recognized by the oil not forming a clear solution in every proportion with alcohol, as is the case with pure oil of cloves.