198 Messrs. Wright and Thompson on the Determination of 
From these average values the following valuations result 
for the voltaic constant for lead in acetate solution of strength 
°25 Pb(C,H30,)2 100 H,O :— 
Yane-lead ts sy Me MR es i 
3 oe 1-091) _. 
Zinc-copper—Copper-lead . « 4 49 5 ¢ = 606 
Mean. «©, . = oum 
Hence, since Thomsen finds that Pb, O, 2C0,H,O,aq.= 
65770, the value of Hy is ‘770, corresponding with 34940 
gramme-degrees, whence 
H—HEy=—'163; 
2. e. the thermovoltaic constant for lead in acetate solution is 
negative, and of nearly the same magnitude as in nitrate 
solution, or in contact with lead sulphate suspended in 
zine or cadmium-sulphate solution of corresponding strength, 
‘25 PbX 100 H,O. In consequence the actual H.M.F. ofa 
lead-copper-acetate cell exceeds that due to the net chemical 
change taking place therein, just as in lead-copper-sulphate 
and lead-copper-nitrate cells. 
Some observations were made on the rate of depreciation 
in E.M.F. with increasing current-density in zinc-lead-acetate 
cells, with the result of showing that the average rate of fall 
is indicated by a curve lying between the analogous curves 
obtained with zinc-silver-sulphate and iron-copper-sulphate 
cells (§§ 130 and 176), being below the former and above the 
latter, which, as already shown, overlie the analogous curves 
obtained with zinc-copper-sulphate and zinc- cadmium-sulphate 
cells. It is remarkable, in this connection, that the thermo- 
voltaic constants for the metals silver, lead, iron, copper, and 
cadmium in these solutions respectively follow in the same 
order as regards numerical magnitude, though not as regards 
sign:— 
@ Silver (in sulphate solution). . =°351 
Lead (in acetate solution) . . —'168 
Iron (in sulphate solution) +:113 to +°148 
Copper (in sulphate solution) . +°009 
Cadmium (in sulphate solution) +°005 to —:010 
Tif. Silver. 
196. The following values were obtained with cells contain- 
ing electro-silver immersed in saturated silver-acetate solution 
opposed to amalgamated zinc and electro-copper immersed in 
their respective acetate solutions, the constant strength being 
‘OD 7 M(C,H;30,). 100 eG < 
