The crystals are completely cleavable along {010}, readily so 
along {O01}. 
On $100} extinction occurs on orientation; on {O10} under 28° with 
regard to the vertical side. The optical axial plane is {010}; at the 
border of the vision-sphere an optical axis is visible on {100}; the 
axial angle is small. The direction of the vertical axis is here the 
axis of the greatest elasticity. 
On $100} etch exerescences were observable with a circumference 
of isorceles trapezia, whose angular points appear to be connected by 
straight lines with a point situated in the centre; this point lies 
nearer to the smallest than to the largest of the two parallel sides 
of the trapezium. They agree with the indicated symmetry. 
Fig. 3: The specitie gravity is 1,692, at 14°C.; 
the equivalent volume is, therefore, 113,4. 
d. 1-4- Dichloro-2-Nitro-Benzene. 
C,H,.Cl.Cl.(NO,) ; Melting point: 54°,5 C. 
4) (1 2 
In most solvents this substance shows 
a very great crystallisation power, but 
measurable crystals are but rarely 
obtainable, as most of the individuals 
exhibit important geometrical deviations 
on account of the great softness of the 
material and often possess curved and 
very dull planes. 
Some time ago the crystal form was 
incompletely determined by Bopnwie; he 
1-4-Dichloro-2-Nitro-Benzene. investigated crystals deposited from car- 
bon disulphide but did not succeed in obtaining combinations admit- 
ting of a complete determination of the crystal parameters (Zeits. f. 
Kryst. 1. 589; Ann. Ch. Phys. (4). 15. 257). 
From acetone I always obtained the largest crystals, sometimes 
some centimetres in length; they are quite of the prismatic type of 
the crystals investigated by Boprwie and possess in addition a lateral 
prism; they exhibit, however, such considerable deviations and are 
generally so opaque that an accurate measurement is out of the 
question. 
I sueceeded best by erystallisation from ethyl-acetate mixed with 
a little carbon-tetrachloride; the pale sherry coloured crystals flattened 
towards {100} so obtained, are very well formed and admit of accurate 
measurement. 
