i 
3 : compounds conditions soon become very intricate. No wonder, therefore, that th 
and that the phellandrene from oil of water fennel may likewise be coven into 
' terpinene. By hydration, an unsaturated alcohol, terpineol, was obtained from dipentene; x 
and a dialcohol, terpin, from limonene. But it had not been ascertained, as yet, where — 
the double bonds were situated and which carbon atom was joined by the hydroxyl 
in the formation of terpineol and terpin from limonene. 
Here, Baeyer found the most suitable sphere where to use ian experience gained 
through the study of hydrated benzene-carboxylic acids and the transformation products : 
of succinylsuccinic acid ester, and so we see how, in his first article, he 2 Eee ty J 
exactly the whole program.” : ; 
A short characteristic follows of Baeyer’s numerous works in the domain of the — 
chemistry of the terpenes and the volatile oils which it would lead us to far to reprint. — 
Rosset 
Sr ae 
Relations between constitution and physical properties of isomeric and homologous — 
hydroaromatic compounds. K. von Auwers who, with his collaborators, repeatedly in- 
vestigated*) the relation between optical behaviour and constitution, has now published 
a treatise concerning hydroaromatic hydrocarbons, alcohols and ketones, and another 
on the relation between constitution and physical properties of isomeric and homologous 
hydroaromatic compounds’). The former investigation was carried out conjointly with ¥ 
R. Hinterseber and W. Treppmann. The bodies described are, with a few exceptions, 
already known, but several of them had, so far, been only examined superficially. Above — 
all, the optical behaviour had to be determined more exactly, as for most substances _ 
the index of refraction had been ascertained only for the D-line and but isolated in- 
dications as to the dispersion were found; in most cases exact determinations of density 
were missing. K. von Auwers and his collaborators investigated samples of different 
manufacture or origin of most of the compounds, in order thus to become independant 
of accidentals in the quality of the preparations as well as in the observations. As 
to the purity of the substances, the authors believe that the saturated hydrocarbons — 
and ketones examined were absolutely pure. For unsaturated hydrocarbons, there exists — 
the theoretical possibility that isomerides may have been admixed, for in most cases Be 
no means is known so far, by which to determine the\absolute purity of alkyleyclo- 
hexenes. The conditions are most difficult with alcohols. It is impossible to separate 
stereoisomeric modifications, if one does not succeed in obtaining them in solid form 
and purifying them by recrystallization. The number of the possible cis- and ‘trans- 
modifications, and further of the optically active or ‘inactive isomerides, rises so quickly 
with the number of substituents, such as alkyl groups, that even with fairly SI 
pee uctory statements are found in literature, e. g. regarding the melting points 
1) See e.g. Reports October 1909, 173; October 1910, 164; October 1911, 122; i Apne 1912, 
October 1915, 62, 76. — *) Liebigs Annaten 410 (1915), 257, 287. 
. om 
