82 Conductivities and Viscosities in Pure and in Mixed Solvents. 



quantity. This, in itself, proves the absurdity of the assumption; 

 consequently, no ratios for solutions 2 and 3^ were calculated. On the 

 assumption, however, that both the ions HIn and In are red, the ratios 

 calculated by equation 15 agree fairly closely with the experimentally 

 determined values. The agreement is as close as could be expected, 

 considering that in work of this character so many different sources of 

 error are possible. The results lead to the conclusion, therefore, that 

 rosolic acid acts as a dibasic acid, and furthermore, show that both the 

 primary and secondary ions are intensely colored. 



In the case of phenolphthalein, it has been shown by Rosenstein that 

 the colored form of the indicator is only produced in appreciable quan- 

 tity where the second hydrogen of the indicator acid is replaced by the 

 base. This is in accordance with the theory already referred to, that 

 the cause of the color production is due to a combination between 

 the metallic phenolate and the quinoid complex, since it is only where 

 the second hydrogen is replaced that the formation of the quinoid 

 phenolate complex is possible. In the case of rosolic acid, however, 

 the quinoid phenolate complex can be found when the first hydrogen 

 of the indicator acid is replaced by the base. The experimental fact, 

 therefore, that the intensely colored form of the indicator is produced 

 when the first hydrogen is replaced by the base, is perfectly in accord 

 with the theories advanced. 



SUMMARY. 



1. An intensification of the red color of solutions of rosolic acid incom- 

 pletely transformed by the addition of alkali, was found to take place 

 when such solutions were allowed to stand, the time reaction being in 

 all probability due to a slow union of the metallic phenolate with the 

 quinoid complex. 



2. In solutions of rosolic acid containing a large excess of alkali a 

 perceptible bleaching of the red color was also indicated. 



3. The ratio (c/ci) of the red to the yellow component has been 

 determined for indicator solutions of various hydrogen ion concentra- 

 tions, using the radiometric method developed in the original article. 



4. The values of the ionization constant of rosolic acid calculated 

 from the ratio c/Ci, on the assumption that the indicator acid is mono- 

 basic, were found to decrease with decreasing alkalinity. When the 

 hydrogen ion concentration was increased from 2.533X1CT 8 to 19.52X 

 10~ 8 , the total salt concentration being 0.0259 normal, the value of the 

 ionization constant K, was found to decrease from 5.65X10' 8 to 

 2.89 XlO' 8 . 



5. It was found that this variation in the constants could be ex- 

 plained by regarding the indicator as a dibasic acid, and it was further- 

 more shown that the intensely colored form of the indicator is formed 

 when the first hydrogen of the indicator acid is replaced by the base. 



