— 159 — 



A study of the data observed by the authors shows that neither the 

 'boiling point nor the density of an alicyclic diene affords any guide as 

 to whether the body is one with conjugated or with isolated double 

 linkings. Determination of the refractive index also is of little value. But 

 by calculating the molecular refraction or dispersion, and by applying 

 the values thus obtained in the testing of the preparations, much better 

 results are afforded. Compensation of antagonistically active influences 

 could only occur in cases where an acyclic diene without conjugation 

 contained at the same time admixtures of a diene with conjugated double 

 linkings and of a cyclic isomeric diene. 



In order to prepare pure acyclic dienes, Auwers and Moosbrugger 

 heated the unsaturated carbinoles with bisulphate of potassium, a mani- 

 pulation in which it is essential to remove the hydrocarbon which is 

 generated as quickly as possible from the reaction-mixture. To achieve 

 this object the best plan is to heat the alcohol and the sulphate under 

 diminished pressure, while simultaneously passing dry hydrogen through 

 the mixture. 



Among other bodies, the authors have spectrochemically examined 

 geraniolene (from geranic acid and from dimethyl heptenol), 2,6-dimethyl- 

 octene-2-ol-6 (from methylheptenone and magnesium ethyl iodide) 1 ), «- and 

 ^-q/cfogeraniolene and homo\ina\oo\ (2,6-dimethyl nonadiene-2,8-ol-6). 



Auwers has also, in collaboration with Ph. Ellinger 2 ), investigated the 

 problem of differentiating between hydroaromatic bodies with endocyclic 

 and with semicyclic double linkings. Wallaces discovery that a semi- 

 cyclic double linking regularly increases the molecular refraction above 

 the normal value was of special importance in the identification of men- 

 thene derivatives. It also appeared to be desirable to ascertain the normal 

 value of the specific exaltation which occurs in menthene hydrocarbons 

 and to compare it with the exaltation values of the several varieties of 

 conjugated systems. 



The authors have re-calculated the observation-material collected by 

 Wallach, using the densities compared with water at 4°, as well as the 

 exact molecular weights and the atomic refractions determined by Eisen- 

 lohr 3 ). Generally speaking, the values for EI D deviated in only a few 

 cases by more than +0,1 from the ascertained mean; hence there was 

 no occasion for determining the refractive index of other methene hydro- 

 carbons, but it was necessary to discover whether these bodies also 

 possessed an increased power of dispersion. 



" As was to be expected, the endocyclically saturated compounds not 

 only exhibit a normal refraction, but also a normal dispersion and the 

 moderate rise of the co-efficient of jrefraction in bodies with a semi-. 



!) See p. 177. 



2 ) Liebigs Annalen 387 (1912), 200. 



3 ) Comp. Report April 1911, 155. 



