ON ABSORPTION SPECTRA OF ORGANIC COMPOUNDS. 243, 



change in absorption takes place with benzeneazophenyltrimethylammoniunit 

 iodide in the presence of acid, although the change is less obvious to the eye.-<' 

 The meet serious criticism of the quinonoid explanation is' to be found in the 

 fact that in concentrated acid the colour is not so intense as in dilute acid, for- 

 it hardly seems scientific to state that a particular configuration is favoured by 

 acid and then to have to agree to a change from that configuration to another 

 when more acid is added. Here again as with the aminoaldehydes three molecular 

 phases exist, one in alcohol, one in dilute acid, and one in strong acid, the 

 primary structure of the molecule being the same in all three. A very analogous 

 case is pararosaniline, which with one equivalent of acid gives a very marked 

 colour, but in the presence of excess of acid the colour and absorption are 

 different. Three phases again are formed, one in alcohol, one in dilute acid, and 

 one in concentrated acid. 



In all probability the above instances are sufficient to indicate the application 

 of the theory of molecular phases to absorption spectra. In conclusion it may 

 be claimed for the theory that it attempts to co-ordinate on a definite physical 

 basis all absorption spectra observations over the whole spectrum between the 

 extreme limits of wave-length 1000/i and 0'1/i, and that these attempts seem 

 to meet with considerable success. 



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US 



