of some compounds of pyridine. 
569 
the ortho-, meta-, and para-compounds show considerable differences 
in their absorption curves. 
These observations suggest that the position of the absorption 
band and its persistency do not entirely depend upon the number 
of atoms introduced into the nucleus. The type and position of 
the introduced atom or group of atoms appear to exert considerable 
influence. In other words, the spatial relationship of the nucleus 
and its side chains must be taken into consideration; and, in this 
direction, the aim of this paper is to describe some investigations 
with several compounds of pyridine. 
The apparatus used in the experiments has been described in 
the previous papers and the method of plotting the curves is 
exactly the same as before. 
Trichloropyridines. The two compounds investigated were 
2:3: 5-trichloro-, and 3:4: 5-trichloropyridines. The latter has 
been previously described by Baker and Baly (loc. cit.): but I have 
examined the absorption curve again so as to make it more com- 
parable with the 2:3: 5-compound under the same conditions. 
The curve obtained from the 3:4: 5-trichloropyridine is essentially 
like that obtained by Baker and Baly. 
With regard to the 2 : 3 : 5-trichloropyridine, it is noticeable 
that the general form of the absorption curve is very like that of 
the 3:4: 5-trichloropyridine, but there are marked differences in 
the position and persistency. The absorption band of the 2:3:5- 
compound is shifted towards the red end of the spectrum a little 
further than that of the 3 : 4 : 5-compound, whilst the persistency 
is considerably increased. The positions of the bands, expressed 
in oscillation frequencies, are: 
2:3: 5-trichloropyridine, 3580, 
3:4: 5-trichloropyridine, 3650. 
