A Comprehensive Treatise on Inorganic and Theoretical Chemistry

104 INORGANIC AND THEORETICAL, CHEMISTRY
observed the single potential of platinum in 0-SiV-Na3AsO4 to be O-983 volt ; in
0-52V-K8AsO4, 0-980 volt ; and in iV-KCl sat. with arsenic trioxide, 0-943 volt ;
and S. Koidzumi studied the potential of platinum in alkaline soln. containing
alcohol ; A. Frumkin and co-workers showed that in the alteration in the potential
of platinized carbon in an atm. of hydrogen from positive to negative with increasing
content of platinum, the metal in the intermediate state is uniformly at the
same potential and not located at an equal number of positive and negative centres.
J. Chloupck found that the potential of a platinum electrode in soln. of ortho-,
pyro-, and meta-phosphoric acid, and arsenic acid, containing mixtures of manganous
and manganic oxides, against a mercury sulphate electrode in 22V-H2SO4,
varied between 0-98 and 1-18 volt, and, at first, increased slowly with time, then
decreased owing to the instability of the soln. H. V. Tartar and H. K. McClain
studied the effect of an electric field ; and R. Audubert, G. E. Muchin and
M. I. Silberfarb, I. Lifschitz, C. Stora, G. Athanasiu, and C. Winther, the
Becquerel effect ; J. M. Ort and M. H. Roepke, the potential in dil. alkaline
sugar soln. ; J. Harty, the potential of a photovoltaic cell in combinations with
ethyl- and phenyl-magnesium chloride ; T. Swensson, the e.m.f. of a cell with a
partition Pt | soln. : soln. | Pt in which one half is kept in darkness, and the other
half illuminated by ultra-violet light. The electrolytes were soln. of several salts.
G. Athanasiu examined the effect of radiant heat on the Pt : PtCl4 : Pt-cell ;
and G. Grube and IJ. Baumeister, that of light and X-rays on polarized platinum
electrodes. Li. V. Nikitin observed that some cells with platinum electrodes appear
to be sensitive to sound.
According to C. Fredenhagen, platinum electrodes in some oxidizing soln.
show a constant potential immediately after immersion, whilst in others it is
variable, and this indicates that the velocity of reaction of the ions of the oxidizing
soln. with the gases absorbed by the platinum is very variable. Tn oxidation
elements, the platinum electrodes always become charged with gases ; in some
cases, the potential measured is entirely due to this gas charge, and is in no way
conditioned by the giving up of electrons from the ion of the solution to the electrode.
The magnitude of the gas charge is dependent on the H "-ion cone, in the liquid, but
the potential of the oxidizing agent is absolutely independent of this. N. E. Loomis
and S. F. Acree prepared platinum electrodes for use as hydrogen electrodes in
0-1 HCl in determining the H"-ion concentration in reacting systems, in which the
deviation from the mean is less than O-l millivolt. H. D. Kirschman and co-workers,
D. J. Brown and J. C. Zimmer, studied the subject. F. Fischer observed that
when external influences are excluded, the e.m.f. of certain open cells of the type :
Cu I CuSO4 soln. I Pt slowly falls to zero, and the same change takes place in a
few hours if the electrolyte be agitated. Cells with mercury or silver in place of
copper behave similarly, but not so with zinc. The change with the copper cell
takes place only at the platinum electrode, and it is assumed that cuprous sulphate
is formed from the metallic copper and the copper sulphate, this in turn involving
a tendency throughout the electrolyte to the separation of copper. The copper
potential is thus transferred to the platinum electrode. The part played by the
cuprous sulphate is illustrated by the fact that by the use of various solutions all
saturated with cuprous sulphate the platinum can be made to assume any potential
between that of oxygen and that of copper. The fall in the e.m.f. of the cell is
attributed to the formation of an alloy of platinum and copper which gradually
becomes richer in copper as the distribution of cuprous sulphate through the
electrolyte proceeds. R. Imther made observations on the same subject ; and
W. J. Miiller and J. Konigsberger found the optical properties of the platinum were
not affected by the reaction in the cell, and this does not support the hypothesis
that an alloy is formed. H. V. Tartar and H. K. McClain referred the electrode
potential to adsorbed films ; R. D. Kleeman and co-workers, the sign of the electrical
layer of a soln. in contact with platinum. E. R. Smith found that the e.m.f. of a
cell with the electrode reaction PtCl4"+2Cl'-PtCl6"4-2e shows reversibility ;