118 Messrs. Wright and Thompson on the Determination of : 
Zinc-Iron. Oadmium-Iron. Silver-Iron. 
ieee 497 Bei 597 
Minimum ......... 483 — ‘167 583 
AVOYARC .....0000008 490 — "157 “592 
Probable error ... +:0030 +:0027 +:0033 
Hence the following three valuations for the voltaic constant 
result ; the values with the cadmium-iron cell being marked 
—, since in this case (as with the corresponding sulphate 
cells, § 175) iron, and not cadmium, actually acquires the 
higher potential. 
ZADC-ArOR 3.5 5 OR eee) ttle 
Zinc-cadmium—Cadmium-iron . { ae = ‘487 
"490 
"592 
Mean. 2 48s 
Julius Thomsen finds Fe, Cl,aq.=99950 for *25FeCl,, 
100H, O; whence Hy='284. Hence the thermovoltaic con- 
stant for bright metallic iron in ferrous-chloride solution of 
this strength is 
H—Hy='488—:284= 4204 ; 
i, €. it.is a considerable positive quantity, as in the case of the 
sulphate-cells. 
It is noticeable that whilst with silver-iron cells the value 
of k,—k, is negative, so that E is considerably less) than 
Hy, the opposite holds with zinc-iron cells, the H.M.F. 
actually set up being not much below double: that corre- 
sponding with the net heat-development in the cell. 
Zinc-silver—Iron-silver . . a Us = 488 
C. Voliaice and Thermovoltac Constants of Metals immersed 
im Solutions of their Nitrates. 
I. Copper. 
188. A number of cells were set up with amalgamated- 
zinc and electro-copper plates, and solutions of the nitrates 
of the respective metals prepared by dissolving pure metals 
in nitric acid, and saturating any excess of acid by means of 
the metallic carbonate freshly precipitated from a portion of 
the respective solution, and well washed. ‘The following values 
were obtamed as the mean readings during the first twenty 
