458 Proceedings of Royal Society of Edinburgh. [sess. 
solution, and readings were taken with the sulphate. The following 
results were obtained : — 
Date. 
Solution. 
Conductivity 
in mhos. 
Ratio to 
Conductivity 
of NH 4 C1. 
July 6 
(NH 4 ) 2 S0 4 
•00339 
'76 
„ 8 
nh 4 ci 
•00445 
1-00 
9 
NH 4 Br 
•00410 
•92 
„ 9 
(NH 4 ) 2 S0 4 
•00370 
•83 
Unfortunately the cement of the tile gave way before the last 
measurements on the sulphate solution were made. The sulphate 
solution had only been in the cell for ninety minutes, whereas, in 
the case of all the other solutions, the cell was left for about 
twenty-four hours before the final readings were taken. The 
same series of experiments was also made in one of the (J cells. 
The results were similar in every respect. 
The ratios of the specific conductivity of the ammonium solutions 
of chloride, ammonium bromide, and ammonium sulphate were 
U00 : U073 : 1-035 ; with the chromic hydroxide film the ratios 
were TOO : '92 : '765. 
C. Effect of a chromic hydroxide film on solutions of sodium 
ammonium d -tartrate, and of sodium ammonium racemate. 
Solutions of sodium ammonium c?-tartrate and of sodium 
ammonium racemate were prepared of such a concentration that 
they had approximately the same specific conductivity as the 
solutions employed in the experiments described in section B. 
The exact ratio of the specific conductivity of the tartrate solution 
to that of the racemate solution was 1 '000 : 1 '046. 
A film of chromic hydroxide was formed with sulphate solutions 
in one of the (J cells, and a series of measurements was taken with 
the three solutions exactly as in the previous experiments. 
With the film, the ratio of the conductivity of the <i-tartrate 
solution to that of the racemate solution was 1 '000 : 1 '040, being 
the same as without the film. 
The conductivities of the two solutions are diminished by 
the film to about the same extent as is that of the sulphate 
solution. 
