±82 Messrs. Smith and Moss on the Contact 
gradual dilution of a saturated solution o£ KCN until the 
p.d. between the drop electrode and the still electrode 
became zero. 
We have found and examined a null KCN solution in 
another way. A normal solution of KCN was made up and 
this, together with weaker solutions of definite strength, 
obtained from it by dilution, was then examined as described 
below. As it was found that the electrocapillary properties 
of solutions, apparently of equal concentration, produced from 
different samples of KCN frequently differed considerably, 
the precise constitutions of the different solutions cannot be 
specified. This, however, is of no importance to the validity 
of the experiments. For the sample of KCN used in the 
experiments, the null solution contained about 026 n KCN; 
but another sample from another source would probably have 
given a different result. 
The following quantities were observed in the case of each 
solution : — 
1. The electrocapillary curve — the reading for maximum 
surface-tension, and the E.M.F. required to produce it, being 
noted as carefully as possible. 
2. The electrocapillary curve of a solution of KC1 of equal 
strength. 
3. The horizontal distance between the descending branches 
of the two curves (cf. Phil. Trans. I. c. p. 69). 
4. The E.M.F. of the cell Hg 
KCN : . KC1 
Hg. 
5. The E.M.F. of the dropping electrode circuit 
Hg J KCN Hg, the measurements being taken when the 
I 
end of the continuous part of the jet was in the surface of 
the solution (Paschen). 
6- The E.M.F. of the dropping electrode circuit 
Hg | KCN 
* 
KC1 I H£. 
Some of the electrocapillary curves are shown in fig. 1, 
the others being omitted to avoid confusion. The KCN 
curves are very flat near the maxima, and the E.M.F.s 
corresponding to these maxima are relatively difficult to 
determine. 
