252 W. Hallock—Smee Battery and Galwanic Polarization. 
the platinum plate is saturated with hydrogen, and the evolu- 
tion is just equal to the diffusion of the gas into the liquid. 
This experiment would seem to show conclusively that the 
values above E=0‘70 D. are not caused by any oxygen which 
may be dissolved in the acid. 
A similar conclusion was reached in a series of experiments 
where the other gases were removed by leading CO, over the 
the acid of its dissolved oxygen.* 
ll the above results are opposed to Exner’s theory, that 
these larger values are due to the oxidation of the evolved 
hydrogen, and rather support the older theory that they are 
due to the small force of the hydrogen polarization which acts 
against the true force of the cell. 
4. EXPERIMENTS ON THE FALL OF THE HELECTROMOTIVE 
Force OF THE SMEE BATTERY. 
When the electromotive force of the Smee is measured in @ 
circuit where the resistance is small in proportion to the siz 
of the cell, i. e. when the density of the current on the platinum 
plate is large, values are obtained which fall decidedly below 
that of H=0°75 D. 
Exner says, this is due to the formation of ZnSO, in the 
cell which has a larger specific resistance than H,SO,, and that 
zinc is precipitated upon the platinum, thus increasing the inter 
a resistance and diminishing the thermal equivalent of the 
cell. 
To test this question a cell was constructed such that the 
zine and platinum were in separate vessels connected by an 1D 
verted U-tube filled with 5 per cent H,SO,, the ends being tied 
up with parchment paper. The vessel containing the platinum 
was furnished with a lid so that CO, could be conducted throug 
the vessel or it could be shut up air-tight. Owing to the large 
internal resistance of such a cell, it was not possible to get 4 
very great density of current on the platinum, still its electra 
motive force fell as low as E=0°81 D. on being short-circuited, 
and rose again in a long circuit, even when the vessel contalD- 
ing the platinum was filled with CO,, as bigh as E=0'92 D 
e 
and finally to E=1°07 D. An analysis proved that th liquid 
* Compare also here C, Fromme, 1. ¢. 
+ F. Exner, Wien. Ber., lxxx, 1879 und Wied. Ann., x, p. 265, 1880. 
zi 
| 
