278 AUSTRALIAN NATIVE PLANTS. 
European practice. It varies in colour from yellowish-green to 
bluish-green ; it is a transparent mobile fluid, with an agreeable 
camphoraceous odour, and bitter aromatic taste, sp. gr. 07926, 
it remains liquid at 13°C., and deviates the ray of polarized light to 
the left. (The author has noticed the oil of every shade of brown, 
but when exposed to the light it in a few days turns to a greenish 
colour.) The green tint of the oil may be due to copper’, 
a minute proportion of which metal is usually present in all that is 
imported. It may be made evident by agitating the oil with very 
dilute hydrochloric acid. To the acid, after it has been put into a 
platinum capsule, a little zinc should be added, when the copper 
will be immediately deposited on the platinum. The liquid may 
then be poured off, and the copper dissolved and tested. When 
the oil is rectified, it is obtained colourless, but it readily becomes 
green if in contact for a short time with metallic copper. 
Guibourt has, however, proved by experiment, that the volatile oil 
obtained by the distillation of the leaves of several species of 
Melaleuca, Metrosideros and LEucalypi/us, has naturally a fine 
green hue. It is not improbable that this hue is transient, and 
that the contamination with copper is intentional, in order to obtain 
a permanent green.”’ (Ma/eria Medica of Western India, Dymock.) 
Oil of cajeput consists mainly of the dihydrate of a hydro- 
carbon, called Cajputene, isomeric with oil of turpentine. On 
submitting it to fractional distillation, dihydrate of cajputene, 
which constitutes about two-thirds of the crude oil, passes over 
between 175° and 178°; smaller fractions, perhaps products of 
decomposition, are obtained from 178° to 240°, and from 240° to 
250°; and at 250° only a small residue is left, consisting of car- 
bonaceous matter mixed with metallic copper. On treating this 
residue with ether, a green solution is obtained, which, when 
evaporated, leaves a green resin, soluble in the portion which boils 
between 175° and 178°, and capable of restoring the original 
colour. (Watts’ Dict. i., 710.) Fora full account of Ca/putene, 
Tsocajputene, Paracajputene, and the salts of Cajputene, see p. 
711-2, loc. cit. 
* This is by no means proved. The question is discussed in almost every treatise on 
Materia Medica. 
