76 



Conductivities and Viscosities in Pure and in Mixed Solvents. 



amount of N/l NaOH indicated in the table, the solutions being in all 

 cases diluted to 100 c.c. The percentage transmissions are given for 

 5 wave-lengths of light between X = 0.56ju and A = 0.58//, which is the 

 region of the spectrum employed throughout this investigation. In 

 certain cases the results of duplicate measurements are given, which 

 indicate in a general way the accuracy of the results. 



TABLE 47. 

 f I/Io depth of solution = 20 mm.] 



Column 2, table 47, gives the percentage transmissions of an indicator 

 solution containing 0.5 c.c. N/l NaOH, the transmissions being deter- 

 mined within a short time after the solution was prepared. Columns 

 3 to 7, inclusive, give the percentage transmissions after the same 

 solution had stood for various intervals of time up to 55 minutes. 

 Columns 8 and 9 give the percentage transmissions of new indicator 

 solutions containing the same amount of indicator and alkali, after these 

 solutions had stood for 5 and 24 hours respectively. It will be observed 

 that the percentage transmissions for any given wave-length of light 

 become constant after the solutions have stood between 1 and 5 hours. 



The fact that solutions of rosolic acid containing an excess of alkali 

 become, on standing, less and less transparent to yellow light, clearly 

 indicates that the concentration of the red component (In) present is 

 becoming greater and greater, with a resulting decrease in the con- 

 centration of the yellow component (HIn); since the greater the 

 concentration of the red component the more opaque the solution 

 becomes to yellow light. 



According to the most recent views 1 concerning the cause of color 

 production by indicators of the aurine type, the color is not due simply 

 to the presence of a quinoid group as such, but to an inter- or intra- 

 molecular combination of the metallic phenolate with the quinoid 

 complex. It is very probably true, in the case of rosolic acid, that this 

 combination between the metallic phenolate and the quinoid complex 

 takes place rather slowly, with a corresponding intensification of the 

 red color. 



It will be observed that the transmission values recorded in column 

 10, table 47, of an indicator solution containing 3 c.c. N/lNaOH are 



'Amer. Chem. Journ., 39, 537, 650, and 651 (1908). 



