The Dispersion and Absorption of Fuchsin 



21 



If n, r% and rs, represent the reflection at the fuchsin-air, 

 fuchsin-glass, and air-glass surfaces respectively and lo the orig- 

 inal intensity of the incident light, the effect of the reflection is 

 to make the transmitted light have the value 



(i— n) {i—n) { \—n) lo, 



neglecting the effect of multiple reflections which does not enter 

 in within the absorption bands. For those colors for which the 

 film is transparent, the effect of multiple reflection is easily al- 

 lowed for to the degree of accuracy possible when working with 

 strongly absorbing substances. 



Knowing the thickness of the film, we may compute the absorp- 

 tion coefficient /x>^ from the following formula : 



Io{ I— n) ( I — ri ) ( I— ;-3) 



/ 



in which -j is the ratio of the intensities as determined by the 



spectrophotometer, / is the thickness of the film, and A the wave- 

 length in vacuo. The photometric measurements were all made 

 upon a film 192 /h/a thick. The transmission of this film is plotted 

 in plate II. Using these values, the curve given in plate I was 

 computed. In the following table these values are compared with 

 Pfliiger's and Walter's results: 

 Values of [i.k 



Walter used Cauchy's formulas for the elliptic polarization 

 which is associated with metallic reflection, and as this could only 



By interpolation. 



121 



