10 Messrs. Wright and Thompson on the Determination of 
the higher potential is of a mixed character (2. e. containing 
two salts), are to a certain extent comparable with Daniell 
cells in which the copper plate is surrounded by a mixed 
solution of zinc and copper sulphates, the only essential dif- 
ference being in the greater solubility of copper sulphate as 
compared with lead sulphate, &c. It seemed of interest, 
therefore, to examine in detail the influence on the numerical 
value of the H.M.F’. of a Daniell cell exerted by addition of 
zinc sulphate to the copper-sulphate solution used. Accord- 
ingly a number of cells were set up containing mixed sulphate 
solutions of strengths mCuSO,, nZnSO, 100 H.0, the values 
of m and n varying in the different cases, but all else being 
the same. The following remarkable results were thus 
obtained, electro-copper plates being used throughout :— 
1. With solutions such that m constantly =1-77, the value 
of a with continually increasing values of n is never nega- 
tive, being sensibly =O as long as does not exceed °5, and 
being +, and continually increasing in numerical value as n 
increases above ‘9. 
2. With solutions such that m does not exceed °5, the value 
of ais always negative, increasing in numerical value as n 
increases. 
3. With solutions such that m= from 1:0 to 1°42, the value 
of a is at first negative, increasing to a negative maximum as 
nm increases, then diminishing to zero, and finally becoming 
positive, and continuously increasing in numerical value. 
Fig. 2. 
Millivolts. 
The following tables represent these results, which are also 
indicated by curves 1 to 6 (fig. 2) ; the values are given in 
millivolts. 
