114 Messrs. Wright and Thompson on the Determination of 
observed values ranged between —:134 and —:187, averaging 
—‘167, that deduced as the above being —:176. 
V. Lead. 
184. A number of cells were examined, set up with elec- 
tro-lead plates immersed in saturated lead-chloride solution, 
opposed (a) to amalgamated zine in zinc-chloride solution; 
(b) to electro-cadmium in cadmium-chloride solution ; (c) 
to electro-silver immersed in silver chloride suspended in 
zinc-chloride solution ; the solution-strength being -05 MCl, 
100 H,0 throughout. The following values were obtained :— 
| Zinc-Lead. |Cadmium-Lead. | Lead-Silver. 
Maximum ......... 596 268 "504 
Minimum ......... | 586 248 -484 
AYVCTASO coh ec ec: ‘591 ‘260 | ‘489 
Probable error .... +:0017 +0023 | +-0024 
These numbers give the following valuations for the voltaic 
constant of electro-lead in the lead-chloride solution :— 
Zinc-lead i debiheiiaed Abyes ii ild Ath ee 
*Zinc-cadmium + Cadmium-lead. °*260+°330 = :590 
*Zince-silver—Silver-lead . . . 1:°080—:489 = ‘591 
Mean = 1990 
Since Pb, Cl, aq.=75970, the value of Eu is *813 (corre- 
sponding with 112840—75970 = 36870 gramme-degrees); 
whence the thermovoltaic constant for electro-lead in satu- 
rated lead-chloride solution is °591—-3813= —°222. ; 
It is noteworthy that whilst 4;—%, is negative for both 
zinc-lead and cadmium-lead cells, so that their electromotive 
forces are notably below the values corresponding with the 
heat-evolution during the net chemical change, the reverse 
is the case for lead-silver cells: here the heat-evolution is 
75970 —58760=17210 gramme-degrees, corresponding with 
°379 volt; whilst the actual H.M.F. is 379+ (—'112) 
—(.--'222)=-489 volt (observed average = ‘489 volt). So 
that whilst lead-silver-sulphate cells give rise to electromotive 
* The zinc-cadmium and zinc-silver values are assumed to be the same 
for the solution-strength used as those above found for somewhat stronger 
solutions ‘°25MCl, 100H,0O; the error thus introduced is but small, if 
not inappreciable. 
