296 PROPERTIES OF ELECTRICALLY CONDUCTING SYSTEMS 



Hantzsch 21 has also studied the absorption of salts of certain organic 

 chromophore groups. In certain of these salts, marked changes have 

 been found and Hantzsch has been able to show that in these cases the 

 change is due to a shift in the equilibrium between two chromophore 

 groups. In the case of salts of certain organic chromophores, however, 

 small differences have been found for which an adequate explanation has 

 not thus far been given. 22 In the following table are given values for the 

 equivalent extinction coefficients for different salts of acetyloxindon. 



TABLE CXXII. 



EXTINCTION COEFFICIENTS FOR DIFFERENT SALTS OF ACETYLOXINDON 



IN WATER. 



X = 436. 



Concentration: 1/100 1/250 1/1250 1/2500 1/5000 

 Thickness of layer: 1 mm. 1 cm. 2 cm. 5 cm. 10 cm. 



Sr . ......... 400 388 390 384 



Li ............ .. .. 347 350 358 350 



Salt 



Na .............. 388 385 390 382 380 



Cs .............. 383 391 387 380 390 



Tl ............... 389 385 381 390 394 



In aqueous solutions, the absorption spectra of the different salts of this 

 acid are very nearly identical with the exception of the lithium salt, 

 whose values appear to be a little low. In the case of all salts, the extinc- 

 tion coefficient is independent of the concentration. 



While the extinction coefficients for the oxindon salts in aqueous solu- 

 tions are the same for all cations, with the possible exception of lithium, 

 in solutions in ethyl alcohol a marked difference has been found. In Table 

 CXXII are given values of the extinction coefficients of different salts in 

 ethyl alcohol. It will be observed that here, again, the value of the co- 

 efficient is independent of the concentration, but that it varies with the na- 

 ture of the positive ion. This variation is unquestionably far in excess of 

 any probable experimental error. The difference might be ascribed to a 

 difference in the optical properties of the un-ionized molecules, and it is 

 known that in these solutions the ionization of these salts is relatively low. 

 However, over the concentration ranges in question, the ionization for a 

 given salt varies considerably, which makes it difficult to account for the 

 constancy of the coefficient at different concentrations. While Hantzsch is 



Hantzsch, Ber. 43, 82 (1910). 



Ztfic/w. /. phya. Chem. 8} f 321 (1913). 



