318 REPORT—1899. 
or pinene (which was shown subsequently to be camphene chiefly),! 
australene, terebenthene, hesperidene, cajeputene dihydrate ; the oils 
of lign-aloe, Indian geranium, santal wood, cedrat, birch bark, juniper, 
rosemary, rosewood, lavender, vitivert, turpentine, cubebs, patchouli, 
citronella, elder, Melaleuca ericifolia, and cedar wood oil ; the hydro- 
carbons extracted from cedrat, nutmeg, caraway, otto of rose, and otto 
of citron and menthol. 
The presence of cymene, a benzene derivative, in some small propor- 
tion, in the hydrocarbons from thyme, lemon, and nutmeg, in the blue oil 
from patchouli, and also in one specimen of the caraway hydrocarbon, 
was proved by the absorption bands characteristic of that substance. 
It was not within the scope of the Report of 1880 to treat especially 
of the relations between the absorption spectra and chemical constitution 
of organic compounds, but the conclusions just quoted must necessarily 
be taken into account, first in connection with the researches of Wallach 
and others on essential oils, and subsequently in the accounts of other 
investigations of absorption spectra which have since been published. 
EssENTIAL OILS AND THEIR CONSTITUENTS. 
That essential oils of the terpene class are related in a certain manner 
to benzene was indicated in a general way by their powerful absorption, 
though their spectra are free from bands. Chemical researches have since 
thrown much light upon their constitution, and shown the nature of their 
relations to benzene, the hydrocarbons being hydrogen-addition products 
of cymene or some other benzenoid derivative. 
It is now known that cymene is p.methyl-isopropyl benzene. By 
fractional distillation cymene had been separated from orange oil, French 
turpentine, and Russian turpentine ; it was believed that these substances 
were largely composed of cymene, that it was in fact one of their constitu- 
ents. It was shown, however, by their spectra that no cymene was contained 
in the first two and but 4 per cent. in the last. The inference was distinct 
and clear that the cymene found was the product of the chemical treatment 
to which these terpenes had been subjected while under investigation,” 
and in connection with the most recently made investigations of this nature 
it is a point of some importance. 
But there were substances in essential oils characterised by very 
powerful absorption bands, and it was concluded that they were composed 
largely of true benzene derivatives or benzenoid hydrocarbons. These 
were the oils of bay, thyme, peppermint, bergamot, cloves, aniseed, cassia, 
carvone, myristicol, and otto of pimento. It was, however, generally 
admitted that eugenol with the constitution C,;H,(OCH;)(C;H,)°OH 
is contained in the oils of bay, pimento, and cloves; that anethol, 
C,;H,(OCH,;)C,H;), is contained in aniseed, and that thymol, 
C,H3(CH;)(C3;H,)*OH, is a constituent of oil of thyme (1:4:3 
hydroxy-cymene) and may thus be represented :— 
Cee fete cH (CH;), 
Ta 
The constitutions of the oils of bergamot and peppermint were unknown, 
1 J. Chem. Soc.vol. xxxv. p. 758, 1879. 
? Thid. vol. xxxvii. p. 676, 1880, Hartley. 
