572 
Mr Purvis , The absorption spectra 
The shift and the persistency of the band may perhaps 
be explained in the following way. If the number of internal 
motions in a given time is greater in the 2 : 3 : 5-compound than 
in the 3 : 4 : 5-compound, there may be a greater absorption of 
light and therefore an increase in the intensity of the band. 
The increased intensity would be revealed not only in the increased 
persistency, but also in the apparent shift of the band towards the 
red end. Or, the position of maximum intensity of the band may 
be altered by an unsymmetrical broadening of the band, for it is 
well known that absorption bands vary very considerably. Some 
are sharp on one edge, and diffuse on the other ; whilst the edges 
of others are unequally diffuse, and therefore the position of 
maximum intensity is not a central one. 
Amido-chloropyridines. The two compounds investigated were 
a-amido-tetrachloropyridine and 7 -amido-tetrachloropyridine. In 
order to compare the absorption curves obtained from these com- 
pounds with that of 5-chloropyridine, I have re-examined the 
latter, and it appears to give a curve very similar to that found 
by Baker and Baly ( loc . cit.). And although there is a general 
similarity in the form of the curves obtained from the three 
compounds, there are considerable differences in the positions and 
persistencies. 
If the curves of the a- and the 7 -compounds are compared, it 
will be seen that the former indicates a considerably greater shift 
of the band towards the red end, and also a considerably greater 
persistency. The band of the 7 -compound is almost wiped out. 
And, on comparing these two curves with that of the 5-chloro- 
pyridine, there is a greater shift of the a-compound and a less 
shift of the 7 -compound. But the persistency of the band of the 
5-chloropyridine is greater than that of the a-compound, and very 
considerably greater than that of the 7 -compound. 
The positions of the bands, expressed in oscillation frequencies, 
are : 
a-amido-tetrachloropyridine, 3050, 
7 -amido-tetrachloropyridine, 3550, 
5-chloropyridine, 3400. 
