( 669 ) 
of the source of light during the measurement the erystals soon 
beeome a dull surface, so that the inaccuracy of the measurements 
is still further increased by the less sharp limitation of the signal 
reflexes. 
Of the substances examined the ortho-dichloroderivatives are both 
rhombic, the mefa-derivatives probably all monoclinic and the para- 
dichloroderivative triclinic; only the geometrically well-defined sub- 
stances of this series are described here in detail. In crystalline 
form they show comparatively little resemblance to each other, 
chiefly in consequence of the considerable deformation of the molecule 
owing to the mutual attraction of the Cl-atoms and of the (NO,)-group. 
Fig. 1. a. 1-2-Dichloro-3-Nitro-Benzene. 
C,H,.Cl.Cl.(NO,) ; melting point : 61° a 62° C. 
(1) @) (3) 
This compound erystallises from a mixture of 
ethyl-acetate and ether and also from glacial 
| acetic acid, on very slow evaporation of the solvent, 
| NE en in colourless silky needles, which are limited by 
IE small, lustrous pyramidal planes (Fig. 1). 
I 
i 
| 
ed 
| 
| 
: li il i Rhombic-bipyramidal. 
el 14 a:b:¢ = 0,6472 : 1 : 0,2780. 
Forms observed : a= {100} and 6 = {010} equally 
ie: strongly developed and both very lustrous; 
EENS ii] p= {230}, m==fl10}, n= {430}; the latter form 
Py edi is the smallest of the three and reflects less sharply 
than p and m; « sometimes shows a delicate 
streak parallel with o:a; 0 ={133! lustrous, 
1-2-Dichloro-3-Nitro. Yielding good reflexes. 
Benzene. The vertical zone is, geometrically very well 
constructed. The angular values observed in different erystals differ 
but ineonsiderably from the average values. 
Measured: Calculated: 
aop = (1.00) (230) 444° 97 — 
ORO (IE: (133) ko Es = 
Pan dd Op 2 11° 14’ 
met (AO) (430) ==) 7 Tk (eral 
ee (Len ONO} 2 27 35!/, 
Dor @00) TAS INS 58246 Sd 
6:30 (OLO: 403) = 74:36 74 34 
0:0 5 
USS wd 15 46 
