HARPER F. ZOLLER 



639 



a small porcelain crucible lid and one drop of a water solution of the 

 indicator was added (0.04 per cent indicator solution). This was 

 compared to the same quantity of indicator in a mixture of four drops 

 of buffer standards (Clark and Lubs standards) plus one drop of 1 

 per cent starch paste, on a similar background. 



r1 



G^l 



To Heater Currant 



^ 



D 



Fig. 1. Viscosiraeter bowl. 



It was later found that the values given by the above method were 

 incorrect and the error was not constant but varied with the indicator 

 and with the region of the pH scale. The hydrogen electrode was 

 used, it consisted of the rocking electrode type described by Clark/o 

 using saturated KCl junction and saturated calomel electrode. 

 The platinum electrodes were first plated with gold and then with 



^^ Clark, W. M., The determination of hydrogen ions, Baltimore, 1920. 



