Potential Differences determined by Null Solutions. 495 
These experiments show that the p.d. Hg | w/lOKCl 
cannot be 0*57 unless, interpreting them according to 
Palmaer's method, the p.d. between h/10 KC1 and w/lOKI 
is nearly a quarter o£ a volt. Such a potential-difference is 
impossible according to the theories at present in vogue 
(cf. Phil. Trans. I. c. p. 62). 
§ 20. Null Solution of KOH. — In attempting to obtain a 
null solution from w/10 KOH it was found that the addition 
of Xa 2 S ('OOln to '002n) produced a gradual shift of the 
maximum to the left which continued over a long time. A 
solution with the maximum at the origin could not be obtained 
conveniently with Na 2 S alone on account of this time effect 
It was found however that if, after the solution had stood 
for some time over the mercury, dilute acetic acid was added 
drop by drop and the solution stirred, the maximum could be 
brought from the left to zero and the time effect was now 
negligible. The results of the experiments with this null 
solution are sriven below : — 
1 
1. 2. 3. 4. 5. 
6. 
Horizontal 
Null Max. S.T. E.JOVfor distance to 
o i . • (scale- mas. S.T. n -, rr[ . 
Solution. L; ading) | lo^Cl curve. 
volt. volt. 
1 sol. i 10 | 
volt. 
1 null 1 , 
| sol I + 
volt. 
■008 
£koh 
+Na 2 S 
+ HC 2 H 3 2 
30-01 
+ •01 '515 
1 
•509 
In considering the value 0*509 volt in column 5 it has to 
be remembered that there is now an appreciable p.d. between 
the solutions. Its value calculated in the usual way is 
n/lOKOH | >i/10KCl = -016 volt at 20° C; and conse- 
quently we now obtain, according to Palmaer's method, 
Hg | 7i/10KCl = '525 volt. But, according to the interpre- 
tation we have offered, this result signifies only that the 
potential reckoned from the solution to mercury at the 
maximum is about *04 volt less in the case of n/10 KOH 
than in that of n/10 KC1. A result which, as before, is in 
agreement with the forms and relative positions of the 
electrocapillary curves. 
2L2 
