( 668 ) 
In oil of cloves as immersion liquid the situation of the elasticity 
directions on the planes of {O10}, {021} and {001} orientated normally 
in regard of the a-axis. The optical axial plane is {100}; the first 
diagonal stands perpendicularly on {010}. On the planes of {021} a 
brightly coloured interferential image is visible in convergent polarised 
light; extraordinarily strong dispersion of a rhombic character with 
0 >v around the first bissectrix. In oil of cloves the apparent axial 
angle amounts to about 49° for the red and 46° for the green vays. 
The oil caused on {021} little solution-figures, which had the form 
of isosceles trapezia; they agree with the indicated symmetry of 
the crystals. 
The specifie gravity is 1,278, at 15°, the equivalent-volume is 
189,28, and the topical axes are: 
Y:W:Ww = 60875: 7,1175 ; 4,3688 
Although differing from NorDENSKJOLD’s para-derivative in symmetry, 
the analogy of the two isomers is still distinctly recognisable in the 
value of the relation 6: c. 
o- Nitrobenzyl-para- Toluidine: a:b:e = 1,000 : 1: 0,6280. 
o- Nitrobenzyl-ortho-Toluidine : a:b: e = 0.8552 : 1 : 0,6138. 
The difference in position of the methyl- and amino-group with 
regard to each other therefore causes chiefly only a variation of the 
crystal parameters in one direction. 
Chemistry. — “On position-isomeric Dichloronitrobenzenes.” By 
Dr. F. M. Janeer. (Communicated by Prof. A. F. HOLLEMAN). 
(Communicated in the meeting of March 25, 1905). 
Of the six theoretically-possible dicbloronitrobenzenes, which 1 
received” some time ago for investigation from Prof. HoLiunman, | 
succeeded in obtaining four in such a measurable form that their 
erystallographieal determination could be satisfactorily undertaken. 
Notwithstanding the great power of crystallisation of most of them, 
the preparation of properly developed crystals is a troublesome and 
very tedious matter. This is partly due to the very great solubility 
in most of the organic solvents, which in connection with the low 
melting points of these compounds often causes a not inconsiderable 
supersaturation. During the spontaneous crystallisation, which then 
takes place, no well-formed individuals, but erystal-aggregates are 
formed, which are difficult of investigation. In addition, the peculiar 
softness of the crystals causes most of them to exhibit curved planes 
and considerable geometrical deviations. Again, owing to the heat 
