ABSORPTION SPECTRA AND CHEMICAL CONSTITUTION. 319 
as likewise those of the substances menthol, carvone, and myristicol, but 
the latter three were said to be isomeric.! 
From the character of its spectrum it was shown that the nucleus of 
menthol was a terpene, while carvone and myristicol were concluded to be 
strictly benzenoid derivatives. Furthermore, a close examination of the 
absorption spectrum of myristicol led to the conclusion that it was a 
mixture of two substances, one only of which was capable of causing 
selective absorption. It was concluded that carvone was really a benzenoid 
Gerivative, oil of peppermint almost entirely so, while bergamot was 
shown to be a mixture of a terpene with a benzenoid derivative. Shortly 
these deductions were arrived at by considering that if a substance which 
shows absorption bands is not a mixture, no repeated fractional distillation 
will show any variations in the intensity of the absorption, or variations 
in the position of the bands in several fractions. 
It was also pointed out that the refraction equivalents, as determined 
by Dr. Gladstone, are abnormal in carvone and myristicol, like those of 
substances derived from the aromatic nucleus. 
The conclusions which were drawn at the time as to the constitution 
of those carbon groupings which can alone give rise to absorption bands 
have been fully justified, not only by purely chemical investigations, but 
also by more recent research into the absorption spectra of closed chain 
carbon compounds of different characters. 
For instance, it was shown by Hartley ? that camphor and benzene 
hexachloride exhibited merely a continuous absorption and no absorption 
band, furthermore that tetra-hydrobenzenes and tetra-hydropyridine or 
their derivatives possessed the same character.3 Referring more par- 
ticularly to the substances in essential oils we have the following classifica- 
tion :— 
Terpenes, C,)H,, or (C;H3),,.. Hydrocarbons, of which there are some 
8 or 10 only as parent substances in essential oils. The terpenes appear 
all to be nearly related by constitution to benzene, being, in fact, dihydro- 
eymenes, C,,H,,(H,). 
Pinene and Camphene Group. 
Pinene, C;)H,, liquid. Camphene, C,,H,, solid. Pinene is the chief 
constituent of turpentine oil from different varieties of pine, eucalyptus 
oil, juniper oil, sage, terebenthene, sylvestrene, and australene. Cam- 
phenes from different sources differ from one another in rotary power ; 
re is derived from terebenthene, austracamphene from austra- 
ene. 
Limonene and Dipentene Group, ©, Hyg. 
Dextro-limonene, C,)H,,, citrene, hesperidene, carvene, the chief 
constituent of cedar oil, cumin and dill oils. In oil of lemons it occurs 
along with pinene. Lzvo-limonene is obtained from Pinus sylvestris. 
Limonene from its reactions is probably a normal dihydro-para- 
' J. Chem. Soe. vol. xxv. p. 1, Gladstone. 
* ‘ Researches on the Relation between the Molecular Structure of Carbon Com- 
pounds and their Absorption Spectra,’ Zans. Chem. Soc. vol. xxxix. p. 153: 
* * Absorption Spectra of the Alkaloids,’ Phil. Zrans. vol. clxxvi. pt. ii. p. 471, 1885. 
‘ Wallach, Anu. der Chemie, vol. coxxs. p. 225; vol. coxxxix. p- 1; vol. cexly. 
p. 241; vol. cclii. p. 106, &c. ;“Ann. der Chemie, vol. coxlvi, p. 236. 
