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reaction arose from the oxygen and hydrogen of the decomposed 
water collecting on the metal plates and changing their electric 
condition with respect to one another ; making them, in short, 
like the two different metals of a voltaic cell instead of one 
and the same substance. This explanation was further verified 
by Grove, who, in 1843, actually constructed a ‘ gas battery/ in 
which the positive and negative plates or poles of the combina- 
tion were both composed of sheet-platinum, but one was sur- 
rounded with oxygen gas and the other with hydrogen. On 
connecting these platinum plates by wire, a current was obtained 
from them, as in the ordinary voltaic cell. 
The liberation of gases which goes on in the secondary bat- 
tery is well shown in the action of the voltameter, Fig. 1. Here 
the current from a voltaic battery with zinc and copper plates, Z 
and C, is passed through a little acidulated water contained in 
Fig. l. 
the vessel V, and the dis-parted gases, hydrogen and oxygen, 
are collected in the inverted tubes, H and 0, the hydrogen ap- 
pearing over the wire connected to the zinc or negative pole 
of the battery, and the oxygen over the copper or positive pole. 
In the secondary battery these gases collect on the metal plates 
which are connected to the poles of the charging battery ; and 
when the latter is removed, the secondary current begins to 
flow, provided always the circuit is completed by joining the 
plate with a wire. The charging current flows through the 
liquid from the copper or positive pole to the zinc or nega- 
tive pole; but the discharging current flows in the contrary 
direction, that is to say, from the plate on which hydrogen was 
deposited to the plate on which oxygen was deposited. Speak- 
ing generally, the secondary current flows through the liquid 
from the plate which was connected to the negative pole of the 
