1098 
and for the way in which he enabled us to complete our investigation 
in the short time at our disposal. 
We also wish to thank Mr. J. M. Bureers for looking after the 
temperature readings, Mr. A. T. van Urk for assistance during the 
whole work and finally him and Mr. Cu. Nicaise for help in the 
calculations. 
Chemistry. — “On the distinction between methylated nitro-anilines 
and their nitrosamines by means of refractometric determi- 
nations’. (ID). By Dr. J.-D. Jansen (Communciated by Prof. 
Ernst COHEN). 
(Communicated in the meeting of February 24, 1917). 
In a former communication *) | called attention to the difference 
in optical properties between coloured nitro-compounds, as nitro- 
anilines and nearly colourless ones as dinitro-benzenes. In the first 
mentioned substances, the molecular-refractions of the isomerides 
showed great differences, whereas the molecular-refractions of the 
isomerides of the colourless compounds were nearly the same. 
This phenomenon proved to be closely related to the light absorp- 
tion. The first group of compounds (the coloured) showed absorption- 
bands in the neighbourhood of the kind of light chosen for the 
determination of the refraction. The refractive-indices and in connection 
therewith, the molecular-refractions of those substances were raised. 
This rise is not the same for the different nitro-compounds, because 
it depends on the place and the depth of the absorption-bands 
(anomalous dispersion). The colourless substances, the absorption- 
bands of which are situated far outside the visible part of the 
spectrum, showed no rise at all of the molecular-refractions or only 
a very slight one. 
By stating this fact we directed the attention to the molecular- 
refractions of the 2.5- and 2.3-dinitro-dimethyl-p-toluidines and the 
respective nitrosamines. 
Spec. Refr. M.-R. A 
2.5-dinitro-dimethyl-p-toluidine 0,2730 | 61,4 18 
7s ia ie 4 5 0,2649 [59,6 ” 
2.5-dinitro-tolyl-methyl-nitrosamine 0,2391 | 57,4 05 
2. Da Meee “ ad 0,2370 | 56,9 |’ 
1) Proc. Roy. Akad. Amst. 564 (1916). 
