compounds obtained from pyridine and collidine. 439 
they are influenced in an opposite direction, by an increase in 
the number and weight of the side chains, by which there is a 
correspondingly decreased persistence. And the weighting may 
be produced either by an increase in the number of radical groups 
as side chains, as for example, in lutidine or collidine ; or by the 
substitution of the hydrogen atoms of these chains by chlorine 
atoms, as in 9-chlorocollidine. 
7 -chlorolutidine. Turning, now, to a substance obtained by 
Sell and Foster from 9-chlorocollidine, and called by them 
7-chlorolutidine, the chemical investigation seems to show that, 
as it is derived from 9-chlorocollidine, six of the chlorine atoms 
have replaced the hydrogen atoms in the two methyl groups, 
whilst the remaining chlorine atom has entered the nucleus. A 
spectroscopic examination of its absorption band was undertaken 
to obtain some further information. The absorption curve has 
been plotted, and on comparing it with the curve of the 9-chloro- 
collidine, it will be seen that the persistence of the band has 
been considerably increased, whilst the shift is not quite so 
marked, but it is greater than that of either collidine or lutidine. 
The persistence also shows a greater increase than that of 
collidine. 
The previous work has shown that, when two or more chlorine 
atoms are introduced into the pyridine nucleus, there is a very 
considerable and gradual increase in the persistence of the bands, 
according to the number of atoms introduced ; whilst, when the 
chlorine enters the side chain, as appears to be the case in 
9-chlorocollidine, there is a decreased persistence. Now, the per- 
sistence of the band of 7-chlorolutidine is certainly less than that 
of either the tetra- or pentachloropyridine. On the other hand, 
it is greater than either collidine or 9-chlorocollidine. And, 
therefore, in the chemical changes from 9-chlorocollidine to 
7-chlorolutidine, the conclusion seems to be that at least one 
chlorine atom has entered the nucleus ; whilst the other chlorine 
atoms have replaced the hydrogen of the two methyl groups of 
the side chains. The net result seems to be caused by the action 
of two forces acting in opposite directions tending to balance each 
other’s influence. 
The shift of the head of the band of 7-chlorolutidine towards 
the red end is 3600, expressed in oscillation frequencies; and 
that of the 9-chlorocollidine is 3580 : i.e. the shift of the former 
is not quite so great as the latter. More exact conclusions can, 
perhaps, be drawn from the gradual shifts of the heads of the bands 
when they are the expressions of a similar series of bodies, like 
the various chlorine derivatives of pyridine already discussed. 
But when the compounds are like those of lutidine and collidine, 
the presence of the implied type of side chain, the replacement ol 
