384 
The absorption spectra of collidine , etc. 
It looks as if all the hydrogen atoms in the three methyl groups 
had been replaced by the chlorine atoms, and that none had 
entered the nucleus. For, if one or more of the chlorine atoms 
had been introduced into the nucleus, we should have expected 
that the persistence of the band would have been greatly in- 
creased ; whereas the persistence is less than that of either 
collidine or lutidine or pyridine. 
On the other hand it might be argued that if the weighting of 
the side chains tends to decrease the persistence of the band, as 
it does in collidine and lutidine when compared with that of 
pyridine, we might have expected that there would have been a 
more marked decrease in the persistence of the band of the 
9-chlor-collidine, if the chlorine atoms had replaced the hydrogen 
atoms of the side chains. 
Further, assuming that one or more of the chlorine atoms 
are in the nucleus, their influence would be to increase the per- 
sistence of the band; whilst the influence of the other chlorine 
atoms in the side chains would be to decrease the persistence, 
and the net result would be a balancing of two influences acting 
in opposite directions. 
Nevertheless, the explanation that the chlorine atoms had 
replaced the hydrogen atoms of the three methyl groups agrees 
better so far with the chemical results of the investigation. 
The shift of the 9-chlor-collidine band towards the red end 
can be compared with the shifts of the bands of the chlorine 
derivatives of pyridine ; the heads of the bands are expressed 
in oscillation frequencies : 
Tri-chlor-pyridine 3650 (Baker and Baly) 
Tetra-chlor-pyridine 3500 ( do. ) 
Penta-chlor-pyridine 3400 ( do. ) 
9-chlor-collidine 3580 (Purvis and Foster). 
These numbers show that the shift of the band of the 
collidine derivative is less than the shifts of the tetra- and 
penta-chlor-pyridines, but greater than that of the tri-chlor- 
pyridine. 
The great shift of the absorption band of the 9-chlor-collidine 
towards the red end of the spectrum agrees with the general 
effect observed by Hartley as regards substituted compounds ; 
that there is a greater shift of the absorption band towards 
the red end, the higher the weight of the group introduced into 
the molecule. 
We are continuing the study of other chlorine derivatives of 
these substances. 
