20 Messrs. Wright and Thompson on the Determination of 
SO 3 aq. =20390, whence the heat of displacement of silver 
from silver-sulphate solution by zine is 85700 gramme- 
degrees=1°890 volt, so that the thermovoltaic constant 
k=HK—H,=15389—1-390= — dol. 
IV. Lead. 
174. A number of cells were examined set up with well- 
washed recently precipitated lead sulphate (prepared from 
clear lead-acetate solution and pure sulphuric acid in excess, 
boiled up many times with distilled water, and washed by 
decantation), suspended in zinc- or cadmium-sulphate solutions 
of varying strength. Hlectro-coated lead plates immersed in 
these magmas were opposed to amalgamated-zine plates 
immersed in zinc-sulphate solution with the following results, 
to which are also joined the figures obtained with similar cells, 
in which electro-copper and electro-cadmium plates immersed 
in solutions of their sulphates respectively were opposed to 
the lead piates. The probable error of each value is in almost 
every instance considerably below +:001 volt, and in no 
case exceeds +'002 volt. ‘The values refer to cells containing 
on both sides solutions of the same molecular strength 
mM” MSO, 100 1eLAG): 
| 
Lead sulphate suspended in ie fi nee aye an 
zinc-sulphate solution. Sb ae ere at 
- phate solution. 
. Cadmium-| Lead- : Lead- | 
Zinc- Lead. Teed Copper. Zinc-Lead. @apeen 
0-1 ‘537 173 “DTT ‘550 564 
0-5 520 ‘160 “594. 537 ‘OTT 
150 ‘512 152 603 *529 D085 
2:0 501 "142 ‘611 ‘b19 596 | 
3-0 491 133 | +514 | 
4-0 ‘487 | ‘509 a 
50 ‘487 "505 
5°75 487 ‘501 | 
From these various cell-values, together with those above 
described for zinc-copper and zinc-cadmium, the following 
valuations are deducible for the voltaic constants of electro- 
lead immersed in a magma of lead sulphate in m ZnSO, 
100 H,O, or in a magma of lead sulphate in m CdSQO, 
100 H,0. 
