Radiometric Measurements of Constants of Indicators. 71 



Kj has been determined and K w is known. The concentration of the 

 quinoid ions Q is given by 



+ _ T[ln (I/Io) - In (I/I,)'] 

 ^ In (I/Io)" - In (I/Io)' 



as explained in equation 19. If the total amount of indicator is T, 



AzOH = T Q. We then have all the data necessary for the calcu- 

 lation of the hydrogen ion concentration in equation 30. The con- 

 centration of the ion A10H in the same equation is given by H -f Q; 

 both of which have been determined. If T' represents the total salt 



added and a its dissociation, Al is (T' A10H) a. 



The following solutions were prepared from mother solutions of 

 methyl orange and aluminium sulphate, the concentrations being 

 1.9865X10 4 and 0.391 gram-molecules per liter, respectively. 



SOLUTIONS. 



I. 50 c.c. methyl orange, diluted to 100 c.c. 

 II. 50 c.c. methyl orange, 5 c.c. AlaCSO^s, diluted to 100 c.c. 

 III. 50 c.c. methyl orange, 7 c.c. A^CSO^s, diluted to 100 c.c. 



j. J.JL. *j\j \j\jt ill c til y i <_*i <3>ii, tij i Vj.v;. JH-i'2 ^kjv^^ 3, VJAIU. uv;a \/\j w \sm\sm 



IV. 50 c.c. methyl orange, 10 c.c. A^CSO^s, diluted to 100 c.c. 

 V. 50 c.c. methyl orange, 0.5 c.c. cone. EfeSO^ diluted to 100 c.c. 



The percentage transmissions given by these solutions are recorded 

 in table 45. 



TABLE 45. 



[I/Io for depth of solution =20 mm.] 



The constants calculated from these percentage transmissions are 

 given in table 46. It has been found 1 that the dissociation of the 

 aluminium sulphate in solutions II, III, and IV is approximately 35, 

 32, and 30 per cent, respectively. 



Carnegie Inst. Wash. Pub. No. 170, 60 (1912). 



