OTHER PROPERTIES OF ELECTROLYTIC SOLUTIONS 295 



It will be observed, from this table, that the values of the extinction 

 coefficients for chromic acid and potassium bichromate are identical 

 within the limits of experimental error. The absorption here is due to 

 the negative ion. It will be noted that the absorption, moreover, is 

 independent of the concentration, which indicates that the negative ion 

 in the un-ionized molecules possesses the same optical properties as in its 

 free state; that is, in its conducting state. The absorption coefficients of 

 the chromate ion are not affected by the presence of acid, but they are 

 slightly affected by the presence of bases. In the following table are 

 given values of the extinction coefficients for potassium bichromate in 

 the presence of varying amounts of potassium hydroxide for the wave 

 length X = 486. 



TABLE CXX. 



ABSORPTION COEFFICIENTS OF SOLUTIONS OF POTASSIUM BICHROMATE IN 

 THE PRESENCE OF POTASSIUM HYDROXIDE. 



Wave Length A = 486. 



Cone. Base 1/2000 1/100 1/1 



f 50 89.9 84.3 83.7 81.7 



V 100 89.0 84.0 83.0 82.3 



[200 89.0 83.6 82.0 81.4 



It will be observed that, on the addition of potassium hydroxide, the 

 absorption of potassium bichromate is affected to a small but measurable 

 extent. Hantzsch has shown that this is due to the formation of other 

 chromophore groups. 



In different solvents, the chromates have identical values of the ab- 

 sorption coefficients, as may be seen from the following table. 



TABLE CXXL 



ABSORPTION COEFFICIENTS OF SODIUM CHROMATE IN METHYL 

 ALCOHOL AND IN WATER. 



A, = 486. 

 V H 2 CH 3 OH 



2000 229 231 



5000 227 233 



The results obtained from a study of other chromophore groups are 

 similar to those obtained in the case of the chromates, and need not be 

 given here. 



