Light Absorption and Fluorescence. 523 



other hand, aniline in solution shows two absorption-band 

 groups and at very small concentration* (N/84,000) the 

 wave-lengths of the centres of these bands are X = 2859*0 

 and \= 2349*5. The values of l/\ are 3496*7 and 4355 

 respectively. From these two measurements it is possible 

 to calculate the most probable values of the fundamental 

 infra-red frequency, v x , of aniline, and of the factor for 

 each band, for we have x x ^=3496*7 (l), yx i/ x =4355 (2), 

 and (?/ — t 6')i/ j; = 758*3 (3), where x and y are integers and 

 y — x is small. It would seem obvious that the only possible 

 values for x and y are 23 and 28 respectively, for the value 

 of v x is then found to be 152*03, 151*97, and 151*65 from (1), 

 (2), and (3) respectively. 



Purvis t has measured the wave-lengths of the com- 

 ponent absorption lines of the less refrangible ultra-violet 

 band group of aniline, and has recorded a strong absorption 

 line at \ = 2859*5, for which 1/X= 3496*1. Itis obvious that 

 the accuracy of measurement of the centre of an absorption- 

 band group is far greater when the centre appears as a 

 single narrow line than in the case of a broad band such as 

 appears in the aniline solution. The value l/\ = 3496*1 may 

 be taken therefore as a more accurate measurement of the 

 central frequency than that obtained from the solution, 

 namely 3496*7. The true value of v x or the fundamental infra- 

 red frequency for aniline is therefore 3496*1 -"-23 = 152*0. 

 The wave-length corresponding to this is 6'5^/x, and it would 

 therefore seem that this gives an explanation of the infra-red 

 band of aniline at 6*68itx referred to above. The benzene 

 band at 6*75//, and the fundamental aniline band would 

 seem to be merged into one band with a mean calculated 

 wave-length of 6*665/x. 



As has already been pointed out, the infra-red absorption 

 spectrum of aniline shows bands due both to ammonia and 

 to benzene; and it follows that the basis constants of both 

 these substances are active in aniline. Now the principal 

 basis constant of benzene is 4, and 38 X 4 = 152; and it would 

 seem therefore that 3*8 must be one of the basis constants of 

 ammonia. If this be so, then many of the infra-red absorption 

 bands of ammonia will occur at frequencies which are mul- 

 tiples of 3*8. This is shown to be the case in Table IV., for 

 eleven out of the sixteen ammonia bands between 3/x and 

 14//, are thus accounted for. 



* The values for a very dilute solution are the same as for the vapour, 

 a fact that will be dealt with in a further paper. 

 + Trans. Chem. Soc. xcvii. p. 1546 (1910). 



