THE TEACHINGS OF MODERN SPECTROSCOPY. 4,77 



other phenomena. They remind one of the slight gradual alterations 

 in pitch which the notes from a vibrating elastic rod undergo when 

 the rod is weighted, or of the change of tone which an organ-pipe ex- 

 hibits when the tube is lengthened." The accompanying woodcut 

 (Fig. 1), copied from Professor Bunsen's paper, may serve to illustrate 

 the shift observed in one of the absorption bands. 



Similar changes take place when some substances like cyanin and 

 chlorophyl are dissolved in different liquids. Absorption bands char- 

 acteristic of these various substances appear, but they slightly vary in 

 position. Professor Kundt, who has carefully examined this displace- 

 ment of absorjDtion bands, has come to the conclusion that as a rule 

 the liquids of high dispersive j^owers were those which shifted the 

 bands most toward the red end of the spectrum. But, though there is 

 an apparent tendency in this direction, no rule can be given which 

 shall be absolutely true whatever the substance which is dissolved. 

 Fig. 2 shows the absorption spectrum of cyanin when dissolved in dif- 



FiG. 2. 



A 



B 



59 CO 



9000 



:ii;iii;isi!;iiii;i 



SEDD 



_J 



"iiiaiiliiilill! 



D 



YELLOW 



ORANGE 



RED 



A = .-.b^-orption of Cyanin in Bisulphide of Carbon, 

 ^ " " Nitrobenzene. 



C= '' " Benzene. 



I>= " " Ether. 



E= " Alcohol. 



ferent liquids. The measurements made by Claes* are employed. 

 We have here an interesting proof that a solution is sometimes much 

 more of a chemical compound than is generally supposed. The sol- 

 vent and the substance must, indeed, be closely connected in order to 

 produce a shifting of the absorption band. On the other hand, it is 

 not astonishing that no general law can be given which connects the 

 displacement with the physical properties of the solvent, for the close- 

 ness of connection depending on the special chemical affinity for each 



* " Wied. Annalen," iii, p. 388, 1S78. 



