On an average they yield from 17 to 22 per cent of volatile oil. At the present time nearly all the oil is produced by means of superheated steam. The bulk of the oil used in this country is distilled here from South American cloves. In Europe clove-stalks are said to furnish a portion of the oil. It is also dissolved by ether and the fixed oils.
Nitric acid reddens it, and when the mixture is heated, oxalic acid is formed.
It is one of the least volatile and most difficult to distill of all the volatile oils. It sinks in water, and is sparingly soluble in it. Its optical rotation is slightly left-handed. By oxidation it yields vanillin, which is also a constituent of the oil. Caryophyllene also occurs in oil of copaiba.