- 87 
by the absorbed, essential oil, is carefully measured in a graduated 
tube and made up to the original quantity; an aliquot part of it is 
next placed in a weighed glass, the solvent evaporated by means of 
a current of air passing over it, and the weight of the residue ascer- 
tained, from which the content of essential oil in the drug can be 
calculated forthwith. 
Mann emphasizes especially as particular advantages of his method 
(which is said to be also suitable for the quantitative estimation of 
essential oils in liqueurs, soaps, and perfumes), that with the use of 
rhigolene it is not necessary to dry the extract (a process which gives 
rise to inaccuracies), because the rhigolene, when shaken with water, 
does not absorb any of the latter. Further errors are prevented b}' 
the use of a definite quantit)^ extraction-liquid, and by taking an 
aliquot part of the solution of essential oil for the determination; 
finall}', the exact moment when the whole of the rhigolene is evapor- 
ated can be fixed with great precision, and errors in weighing caused 
by the presence of some remaining solvent, can thus be entire!}' 
obviated. 
Hydrocarbons. 
Cyclogeraniolene. The similarity in the physical properties 
between pulegene andTiemann's cyclogeraniolene, as also the similarity 
between the ketonic acids formed from both hydrocarbons on oxidation, 
led Wallach to the conclusion that a thorough comparison of the two 
compounds was necessary, by which the absolute difference between 
the two bodies was established^). Tiemann's assertion that, when 
cyclogeraniolene was produced from acyclic hydrocarbon, chiefly a-cyclo- 
geraniolene was formed, could be confirmed; the same investigator was 
also able to demonstrate, that the a-compound yields a nitrosochloride 
and a nitrosate characterised by the property of only dissolving with 
great difficulty. When boiled with alcoholic potash liquor, these com- 
pounds yield trimethyl cyclohexenonoxime C9 H^^ N O H, which, on being 
decomposed with acids, yields the unsaturated trimethyl cyclohexenone 
QHj^O. This ketone passes over by reduction into saturated trimethyl 
cyclohexanol, which can be converted by oxidation into trimethyl 
cyclohexanone 
H2C.CH2 .CO 
(H3C),C.CH,.CH.CH3 
That this body actually represents a derivative of a-cyclogeraniolene, 
is proved by the fact, that on oxidation it first of all yields a ketonic 
acid with the same content of carbon, but next ^, /5-dimeth}'l adipic acid. 
^) Liebigs Annalen 324 (1902), 97. 
