Radiometric Measurements of Constants of Indicators. 



79 



RESULTS WITH ROSOLIC ACID. 



For the first determination of the indicator constant K< the following 

 series of solutions was used: 



SOLUTIONS. 



No. 1. 50 c.c. rosolicacid; 25 c.c. Na 2 HPO 4 ; 5 c.c. HC1, diluted to 100 c.c. 

 No. 2. 50 c.c. rosolic acid; 25 c.c. Na 2 HPO 4 ; 10 c.c. HC1, diluted to 100 c.c. 

 No. 3. 50 c.c. rosolic acid; 25 c.c. Na 2 HPO 4 ; 15 c.c. HC1. diluted to 100 c.c. 



These solutions were prepared from the stock solutions, the concen- 

 trations of which have already been given. All solutions were allowed 

 to stand for 24 hours, which time, according to the results of the prelimi- 

 nary work, was amply sufficient for equilibrium to be established. In 

 table 50 are given the percentage transmissions for a depth equal to 

 20 mm. of each of these solutions, the values being in every case the 

 average of two measurements. These are the values to be substituted 

 for (I/ Io) in equation 6. As has previously been explained, the ratio 

 c/d also depends upon the percentage transmission (I/Io)" of an indi- 

 cator solution completely transformed into the red component, and 

 also upon the percentage transmission (I/ 1 )' of an indicator solution 

 completely transformed into the yellow constituent. The transmissions 

 (I/ lo)" used are the averages of those recorded in columns 2, 3, and 4, 

 table 48. It was found that solutions containing 50 c.c. of the stock 

 solution of the indicator plus the necessary amount of hydrochloric 

 acid to convert the indicator entirely into the yellow component were 

 completely transparent to the 5 wave-lengths of light used. The 

 transmissions (I/ ID)' are therefore in every case 100 per cent. 



TABLE 50. 



In table 50 the ratios G/CI = (In)/(HIn) were calculated from equa- 

 tion 6 and the constants K t from equation 1. The hydrogen ion con- 

 centrations were calculated by means of equation 7, a x and a 2 being 

 interpolated from the percentage ionizations of monosodium and 

 disodium phosphates at various dilutions given by Abbott and Bray. 1 



Another series of solutions described below was prepared and 

 allowed to stand 16 hours, in which time all of them had come to 



'Amer. Chem. Journ., 31, 729 (1909). 



