470 Intelligence and Miscellaneous Articles. 
dulated water or solution of chloride of sodium, a constant couple 
with a single liquid is formed, without a diaphragm. But usually 
the cylindrical form, combined with the use of a cloth or porcelain 
diaphragm, is preferable. 
All samples of sulphate of lead are not alike, probably from the 
presence of foreign admixtures ; some become very hard, others do 
not acquire a sufficient resistance. Without knowing on what this 
depends, a mixture of 100 grammes of dried and pounded sulphate 
of lead, 20 to 30 grammes of chloride of sodium, and 50 cubic centi- 
metres of saturated solution of chloride of sodium, gives good re- 
sults: the addition of 20 to 25 grammes of oxide of lead (minium 
or massicot) increases the hardness of the mass. Another method 
cf using the different sulphates of lead is perhaps preferable. It 
consists in coating the freshly moulded sulphate of lead with a thin 
layer of plaster. This mass being placed in a liquid in the interior 
of a hollow zinc cylinder, constitutes a couple; in this way the sul- 
phate does not get out of shape, nor is there any necessity for a 
diaphragm ; the plaster serves this purpose, and prevents the con- 
tact of the zine and the reduced lead. 
In these couples either water acidulated with sulphuric acid, or 
solution of chloride of sodium may he used; in the latter case the 
electromotive force is somewhat greater than in the former, but the 
solubility of sulphate of lead in it causes a deposition of reduced lead 
on the zinc, which must be removed from time to time. With 
acidulated water this is not the case. 
The electromotive force of these new couples, as compared with 
that of a zinc-platinum couple, water containing one-tenth of acid, 
and nitric acid, is as follows :— 
Gowpler with, mitra Wei: Yerab er 32). rae tee eae 100 
Couple with sulphate of copper .................... 58 to 59 
Couple with compact per With solution of chloride of 
stute sodium» 2.) hawle ov Sadl 2ee 
meable sulphate of lead) With water acidulated with 
sulphuric acid.......... 27 
In the first moments of the action the electromotive force de- 
pends on the nature of the conductor in contact with the sulphate 
of lead; but as soon as there is metallic lead reduced, it attains a 
constant value. When these couples are in operation, the sulphate 
of lead is reduced to the metallic state—the sulphuric acid from it 
forming sulphate of zinc: the lead may be obtained by fusion. 
From the chemical equivalents we réadily get the relative weights 
which the two electrodes must possess in order tu have a constant 
current; 100 grammes of zinc require470 grammes of sulphate of lead. 
These solid masses, permeable to liquids and employed as negative 
electrodes, by preventing polarization play the same part as the per- 
oxides of lead or mangauese, nitric acid, and reducible metallic salts ; 
but their resistance to conductibility, which varies with the progress 
of the reduction, prevents the application of these couples with a 
single liquid to the same uses as nitric acid couples. ‘They may, 
however, be used with advantage where piles of great resistance 
and long duration are required.— Comptes Rendus, April 2, 1860. 
