The Dispersion and Absorption of Fuchsin ii 



truni it is established beyond a doubt that the vakies given by 

 Pfliiger do not apply to the fuchsin upon which my measure- 

 ments were made. The fact that Pfliiger Obtained the same 

 values using prisms of different angles seems to show either 

 that the two methods lead to different results, or that the com- 

 position of the two samples of fuchsin was different. There are 

 a number of red triphenyal men thane dyes of distinctly different 

 compositions, all of which go under the name of fuchsin. 

 Wernicke^ obtained the dispersion curve of a fuchsin by the 

 prism method and found the indices to range from 1.31 to 1.90. 

 The one on which the writer's first work was done had indices 

 ranging from less than unity to about two, Kundt experimented 

 on a fuchsin having two absorption bands in the visible spec- 

 trum. However, there is no doubt but what the fuchsin in ques- 

 tion was made by the same process as that which Pfliiger used, 

 though, having been purchased seven years later, it was probably 

 made in a different batch, and hence there is a possibility of the 

 composition being slightly different. 



The agreement with Walter in the red is extremely satisfac- 

 tory. The two curves run uniformly parallel to one another, 

 this writer's being a little higher than Walter's, which may be 

 accounted for by an error in the thickness of a systematic error 

 of some kind. A slight change in the thickness would make the 

 two curves almost identical. 



The thickness of the films was determined as follows : A por- 

 tion of the film is washed away with alcohol, leaving a clean, 

 sharp edge. In general, when a film is thus washed away, there 

 is a concentration of fuchsin at the edge, due to a flowing of the 

 solvent. This is of course undesirable and was eliminated by 

 using a piece of blotting paper with which to clean away the 

 fuchsin. This piece of blotting paper was itself cut to a clean 

 sharp edge and slightly dampened with alcohol. The glass near 

 the film was wiped with it, a new edge of the blotting paper was 

 prepared,' dampened, and the operation was repeated until a sat- 

 isfactory edge of fuchsin was obtained. 



Now a plate of glass was placed upon the glass upon which 



^Fogg. Ann., 155. 1875. 



Ill 



