( 174 ) 



Indicator : metanilyellow-acicl. The change in colonr of this indicator 

 on dihition Avas not strong enongh. Therefore, tiie sohition was mixed 

 before use, with a few drops of hydrochloric acid, which caused the 

 difference in colour to be more decided and more readily observable. 

 This addition may be made without fear, for the colour is used as 

 the indicator for the concentration of the hydrogen-ions and an equal 

 concentration of the hydrogen-ions always gives the same colour. Only 

 we must take care to use the same indicator solution for the whole 

 series of determinations. 



Found : 



15 cc of indicator -{- 50 cc of water. Colour again restored with 

 9 cc salicylic acid solution, therefore: 



50 4- 9 



—- X 150 = 983.5 = Vs 



9 



15 cc of indicator -\- 10 cc of water. Colour again restored with average 

 22.5 cc of benzoic acid solution, therefore 



10 + 22.5 



22.5 

 from which : 



0.00102 



X 100 = 144 = Vo 



- 1 + / + 1 



'^ '0.00102X983.5^ 



= 0.0006294 



and : 



144 1 - 0.0006294X983.5 



983.5 * 1 — 0006294X144 

 By the electrolytic process the value of Kb = 0.00006. ') 



Kb = 0.00102 . ^rr:r-z • — ' ., \ . . = 0.000063. 



Determination of the dissociation constant of anthranilic acid. 

 Given: Kt = 0.00006 n = 200 



Va = 100 

 Indicator : methylorange-acid. 



Found: 



15 cc of the indicator in both cases diluted with 50 cc were titrated 

 back to the original colour. 

 For this was required 

 Benzoic acid : 0.87 cc 

 Anthranilic acid : 1 .56 „ 



1) Nernst. Theoretische Chemie, p. 404. 



