440 Mr Purvis, The absorption spectra, etc. 
the hydrogen of the side chains by chlorine, or if, in addition, 
there are one or more chlorine atoms in the nucleus, all these 
factors may make the problem more complex. Nevertheless, the 
study of the increase or decrease in the persistence of the bands 
seems to be of some importance in reference to the constitution of 
substances : and the shifts of the bands by increasing the weight 
of the groups entering the nucleus, and also, it may be, the type 
of the substituted group, should be of additional value. 
I have to thank Dr Sell for kindly giving me some of the 
substances examined : and also Mr W. H. Foster, who was good 
enough to make the solutions therefrom. 
