

92 Report of Schimmel § Co. 1921. 



In a further paper Eisenlohr 1 ) reports on the precalculation of the index of refraction 

 in the case of aromatic hydrocarbons. The values for the expression M X n D20 o showed, 

 in the case of the benzene hydrocarbons, a number of regularities, the enumeration 

 of which would carry us too far. These intimate relations between the observed and 

 the calculated molecular index of refraction admit, with the help of the "E" value 

 of any compound (excess, positive or negative, resulting for the expression MXn D20 o 

 with regard to the sum of the constants for branch chains and for rings), of calculating 

 the "E" value and hence the refractive index for any other aromatic hydrocarbon. The 

 introduction of side-chains into the benzene ring led to excesses, the amount of which 

 depended upon the number and the mutual positions of the substituents. The neutral 

 conjugation of the three ethylene bonds in the benzene nucleus (Briihl) was eliminated 

 by the entry of side chains, and the now starting conjugation-effect of the ethylene 

 linkage gave the excesses. Such conjugation effects were in general indicated in the 

 expression of the molecular coefficient of refraction by the excess of the observed 

 values over the calculated figures. The inter-relations, established for benzene hydro- 

 carbons, between the molecular coefficient of refraction and the constitution do not 

 represent any special case, limited to this class of substances. In other cases, however, 

 as, for instance, with the cyclohexanes, the observed values extant were not always 

 sufficiently reliable. 



W. Deutschmann 2 ) has investigated the deviations of the optical rotation from the' 

 law of Biot, according to which the specific rotation of an active substance is the 

 same for all concentrations and for all solvents (molecular rotation). He finds that 

 these deviations can be traced back to the formation of compounds between the solute 

 and the solvent, or to changes in the degree of association. 



In order to determine the cliamagnetism of solid odorous substances H. Zwaardemaker 

 and F. Hogewind 3 ) incorporated these materials by spraying them into paraffin of 

 known diamagnetic susceptibility. Their diamagnetism could then be compared with 

 the diamagnetism of the liquid substance or its solution in water. The values found for 

 the solid substances corresponded to those previously observed for the liquid materials. 



Botanical Notes. 



In a communication on the production of medicinally-valuable species of plants by 

 selection W. G. Smith 4 ) points out that the breeding of plants, important in agriculture, 

 has made more progress than the cultivation of medicinal plants. Whilst the agricultural 

 cultivation was being promoted by the governments and larger public bodies, which . 

 publish their results, the nursing of medicinal plants was mostly in private hands which 

 keep their experience and methods to themselves. 



Larger specimens could be obtained by suitable manuring and careful attention 

 to the plants, but properties like the quality and the proportion of the efficient con- I 

 stituents could only be influenced by selective breeding. Qualitative changes could 

 already be attained by mass selection, by mixing a number of selected specimens with 

 the more common kinds. The best results were, however, realised by selecting superior 

 specimens and by propagating from them in true breeding. The hybrids are particularly 



!) Berl. Berichte 53 (1920), 2053. — 2 ) Zeitschr. f. physik. Chem. 95 (1920), 385. — 3 ) Archives ne'erland. 

 d. Phys. de Vhomme et des animoux 4 (1920), 224. From Chem. ZentralbJ. 1920, IV. 507. — *) Perfum. Record 

 11 (1920), 144. 



