452 



DE. R. B. DENISON AND DR. B. D. STEELE ON THE 



no basic dye was found sufficiently free from hydrolysis to be of any use as a cation 

 indicator. It was ultimately found that, by the use of very high voltages, distinctly 

 visible refraction margins could be obtained in solutions as dilute as 0'02 N. 



Method of Experiment. 



The placing of the two indicator solutions in contact with the middle electrolyte 

 without appreciable mixing taking place, and without using gelatine or other 

 membrane during the experiment, presented considerable difficulty. The ordinary 

 method of pouring the one solution upon a thin piece of cork floating on the other 

 solution was found to be quite unsatisfactory. The problem was finally solved by 

 the use of the apparatus shown in figs. 1 and 2. It consists of two parts which are 



\ 



Fig. 1. 



Fig. 2. 



joined together at G or G'. If both indicators are lighter than the solution to be 

 measured, the apparatus is made up of two halves of the form shown in fig. 1. If 

 both are heavier, then both halves are of the form shown in fig. 2. If one indicator 



