Uniformity of the Charge.—New and old Plates. 123 
ferent portions of fluid constituting the necessary electrolyte, 
in the cells. 
1143. Uniformity of the charge.—This is a most important 
point, as I have already shown experimentally (1042. &c.). 
Hence one great advantage of Dr. Hare’s mechanical arrange- 
ment of his trough. 
1144. Purity of the zinc.—If pure zinc could be obtained, 
it would be very advantageous in the construction of the vol- - 
taic apparatus (998.). . Most zincs, when put into dilute sul- 
phuric acid, leave more or less of an insoluble matter upon 
the surface in the form of a crust, which contains various me- 
tals, as copper, lead, zinc, iron, cadmium, &c., in the metallic 
state. Such particles, by discharging part of the transferable 
power, render it, as to the whole battery, local; and so dimi- 
nish the effect. As an indication connected with the more or 
less perfect action of the battery, I may mention that no gas 
ought to rise from the zinc plates. ‘The more gas which is 
generated upon these surfaces, the greater is the local action 
and the less the transferable force. ‘The investing crust is also 
inconvenient, by preventing the displacement and renewal of 
the charge upon the surface of the zinc. Such zinc as, dis- 
solving in the cleanest manner in a dilute acid, dissolves also 
the slowest, is the best; zinc which contains much copper 
should especially be avoided. I have generally found rolled 
Liege or Mosselman’s zinc the purest; and to that circum- 
stance attribute in part the advantage of the new battery 
(1134.). 
1145. Foulness of the zinc plates.—After use, the plates of 
a battery should be cleaned from the metallic powder upon 
their surfaces, especially if they are employed to obtain the 
laws of action of the battery itself. This precaution was al- 
ways attended to with the porcelain trough batteries in the 
experiments described (1125. &c.). If a few foul plates. are 
mingled with many clean ones, they make the action in the 
different cells irregular, and the transferable power is-accord- 
ingly diminished, whilst the local and wasted power is in- 
creased. No old charge containing copper should be used to 
excite a battery. 
_ 1146. New and old plates.—I1 have found voltaic batteries 
far more powerful when the plates were new than when they 
have been used two or three times; so that a new and a used 
battery cannot be compared together, or even a battery with 
itself on the first and after times of use. My trough of twenty 
pairs of four-inch plates, charged with acid consisting of 200 
water, 4} oil of vitriol, and 4 nitric acid, lost, upon the first 
time of being used, 2°32 sane per plate. When used 
2 
