The Dispersion and Absorption of luic/isin 



II. — The Anomalous Dispersion and Selective Absorption of 



Fuclisin ^ 



BY W. E. CARTMEL 



Although fuchsin is the substance in which anomalous disper- 

 sion was first observed, and although it shows this phenomenon 

 much more decidedly than any other substance upon which it 

 has been found possible thus far to make anything like reliable 

 measurements, its optical constants have not yet been fully deter- 

 mined except by indirect methods. Very complete absorption 

 curves have indeed been given for solutions of different concen- 

 tration, but not for solid fuchsin. 



It was therefore thought that it might be of interest to deter- 

 mine the absorption and dispersion directly, both of these upon 

 the same identical fuchsin ; and as a very good determination of 

 the dispersion curve has already been given by Pfliiger,- who 

 measured the deviation produced by a thin wedge of solid fuchsin, 

 it was decided to redetermine this, using interferential means. 

 This would present the advantage of a redetermination by a dif- 

 ferent method, and, furthermore, the methods of absorption and 

 dispersion could both be made upon the same fluid. 



Films were therefore prepared in the usual way by dipping 

 glass plates into an alchoholic solution of fuchsin and allowing 

 the alchohol to evaporate. The fuchsin upon which the first 

 experiments were made was some that had been purchased for 

 general laboratory purposes, and it was found that the dispersion 

 and absorption had values very much lower than those given by 

 Pfliiger. Some fuchsin of the same kind as that which Pfliiger 

 had used was therefore imported from Kahlbaum in Berlin, and 



^Read before the Washington meeting of the American Association for the 

 Advancement of Science. 

 =^ lyied, Ann., vol. 65, p. 203. 1898. 



lOI 



