973 
Contrasting with these great differences in molecular refractions 
of isomeric nitro-anilines, we find that those of dinitro-benzenes and 
_nitro-toluenes are practically the same. 
1.4 Dinitro-benzene. M-R. — 39,2 1.4. Nitro-toluene. M-R. = 38,1 
1.2 5 . keke ll SA 7 i Mie! 
1.3 a re hp See as Kf) 5 rs ca haere Te 
The explanation of this difference in properties between the two 
last-mentioned groups and the nitro-anilines and -toluidines is 
possible, when we take into consideration the light-absorption. 
The absorptioncurves of several substances [ used are known. 
All the nitro-anilines and nitro-toluidines have an absorption band 
— sometimes a very deep one — near the visible part of the 
spectrum, whereas in the dinitro-benzenes and nitro-toluenes this 
band has either disappeared or is situated a long way off, in the 
ultraviolet. 
le) 
As an example may serve (A in Angström-units): 
o-Nitro-aniline. ') Shows a deep band (A + 4080) and a 
shallow one (A + 2800). 
m-Nitro-aniline. 7) Shows a band (4 + 3700). 
p-Nitro-aniline. ®) Shows a very deep band (4 + 3840). 
The molecular refractions of these compounds are, as has already 
been stated, very different. 
o-Nitro-toluene. *) Shows a band (4 + 2450). 
m-Nitro-toluene.*) — ,, st Sta Lee 260801, 
p-Nitro-toluene. *) 3 eet Yate (dend LOO): 
The molecular refractions are almost equal. 
o-Dinitro-benzene. *) Shows no band between 2 4000 and 2 2000. 
m-Dinitro-benzene. ‘) Shows no band. 
p-Dinitro-benzene. *) Shows a band (4 + 2560). 
Also with the following, nearly colourless, compounds having no 
absorptionband in the visible part of the spectrum, the isomerides 
have almost similar molecular refraction. 
o-Xylene ®)  M-R. = 35,74 o-Toluidine *) MER; == 00 
m-Xylene i 35,90 m-Toluidine 3 DO en 
p-Xylene 99,99 p-Toluidine “a 35,99 
1) Purvis and Mc. CLELAND. J. Chem. Soc. 103, 1104 (1913). 
) 
2) Baty, Tuck and MARSDEN, , . „ 97,-582 (1910) 
3) ” ” ” ” ” ” ” ” 572 ” 
4) Purvis and Mc. CLELAND, , A „ 103, 1100 (1913). 
5) LANDOLT-BöRNSTEIN p. 1032 and 1033 (1912). 
