ABSORPTION SPECTRA AND CHEMICAL CONSTITUTION. 321 
Carvone, C,)H,,O (formerly carvol), is isomeric with carvacrol, but it 
is a ketonic derivative of a dihydro-cymene. 
Jo CO. 
\oH=cH”’ 
Tt will thus be seen that a marked distinction is to be drawn between 
the constitution of those substances in essential orls which are characterised 
by a continuous absorption, and those which exhibit the peculiarity of 
absorption bands; while the former belong to what has been termed the 
hydro-aromatic group, the latter are true derivatives of the aromatic series. 
The original conclusions have thus been confirmed. 
Without entering into details of their structural formule in each case, 
it may be stated that none of the hydroxy-derivatives, or other oxy- 
derivatives, of the hydro-aromatic group exhibits absorption bands. Of 
substances which were examined the following examples may be 
referred to : 
Citronellol, 
(CH,).C : CH: CH, - CH, ‘CH(CH,) : CH, ‘CH, -OH 
in rose, pelargonium, and geranium oils, and menthol, which has already 
been referred to, 
C,H, C CH - CH, 
CH(OH):CH, 
CH ‘CH, 
OH,),CH :CHY 
( 3)2 \cH, J CH,/ 
both belong to the group of camphors with the general formula C,,H,,,0. 
We have next the substances occurring in the oils of cajeput, euca- 
lyptus, citronella, geranium, lemon, lign-aloe, and neroli. 
Cineol, 
/ CH, * CH3\. 
(CH;),CH ‘-C——_—O —C:CH, 
\ CH, * CH, / 
Citronellal occurs in rose, pelargonium, and geranium oils, 
(CH;),C : CH :CH, ‘CH, -CH(CH,)-CH, - CHO 
Geraniol (lemonol), 
(CH,),0 : CH : CH, -CH,* C(CH,) :CH-CH,: 0H 
Lign-aléol, 
(OH;,),.C : CH - CH, CH, : C(CH,;) (OH) :CH : CH, 
Nerolol, from oil of neroli, is believed to be identical with géraniol 
These belong to the class of camphors with the formula C,,H,,,_.O0. 
Note.—The absorption spectra of stereo-isomeric compounds have not 
up to the present yielded any indications which serve to distinguish 
between those which are levo- and those which are dextro-rotatory, or, on 
the other hand, those which are inactive. In this respect there is a great 
tae between position isomerism and stereo-isomerism. The reason 
Y 
