ATTEMPT TO REPLACE THE MERCURY DROP ELECTRODE WITH SOLID METAL ELECTRODES

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• Collection: General CIA Records
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• Original Classification: C
• Document Page Count: 6
• Document Creation Date: December 22, 2016
• Document Release Date: September 27, 2011
• Sequence Number: 614
• Publication Date: January 30, 1951
• Content Type: REPORT

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INFORMATIOPt~1FROM,I,; ,
[,SIO BROADCASTS CD NO.
FOREIGN DOCUMENTS OF12''pi
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SUBJECT Scientific - Chemistry, production control
appliances
HOW
PUBLISHED Book
WHERE
PUBLISHED Moscow/Leningrad
DATE
PUBLISHED 1943
LANGUAGE
CENTRAL INTELLIGENCE AGENCY REPORI
CLASSIFICATION CONFIDENTIAL
DATE OF
INFORMATION 1943
DATE DIST. 3o Jan 1951
NO. OF PAGES 6
SUPPLEMENT TO
REPORT NO.
THIS IS UNEVALUATED INFORMATION
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OF ITS CONTENTS IN AR( MANNER TO AN DIIAUTHORISED PERSON 15 PRO'
HIMITOD ST LAW. REPRODUCTIOA OF THIS FORM IS PRONIGITRO.
Trudy Vseso zno Konferentsii o Analiticheskoy Khimii (Works of the
All-Union Conference on Analytical Chemistry), Vol II, pp 551-558,
Academy of Sciences USSR Press, LC No 71.V8 1939..
ATTEMPT TO REPLACE THE MERCURY DROP ELECTRODE
WITH SOLID METAL ELECTRODES
S. D. Miller
All-Union Sci Res Inst of Geol
Leningrad
f7igures referred to are appended]
The experiments of certain researchers, well-known from literature (Ya.
Heyrovskiy, Polarographic Method - Theory and Practical Application fPolyaro-
graficheskiy method - teoriya i prakticheskoye primeneniy /, ONTI, 1937), to
replace the mercury drop electrode for polarographic analysis with electrodes
of a solid metal were based, in the main, on the principle of the mechanical
elimination of results of physical and chemical changes taking place in the
solution and on the surface of the polarized electrode during electrolysis.
We tested another method for using solid electrodes in their polariz-
able state, this application being based on their periodic depolarization
through an electrochemical process.
electrodes of small surface area (relative to the "unpolarized" large elec-
trode) which are kept simultaneously in the solution being tested. In each
period when one of the small electrodes is polarized, the remaining are short
circuited with the large electrode having a potential opposite to it; in this
manner each is subjected to periodic depolarization, after which they suc-
cessively enter into the process in a "regenerated" state.
In Figure 1 is given the principal circuit for cathode polarization with
two small electrodes, the circuit which served as the subject of our investiga-
The procedure of this method is as follows:
The polarizable electrode is represented alternately by two or more solid
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The systems of electrodes which were used consisted of: (a) a large
mercury anode and two small electrodes of platinum amalgam, and (b) a large
platinum electrode and two small platinum electrodes.
A system of two small platinum electrodes and a large mercury anode
also was tested. The dimensions of the separate pairs of small electrodes
were varied within the following limits: diameter of the electrode - 0.5,
0.3, and 0.1 mm; length - from v"6 to c~? 0.5 mm.
The switching over of the small electrodes as shown in the diagram is
accomplished automatically with the help of a throw-over switch of extremely
light construction (of the "spider" type), devised by us for this circuit,
whose throwing over to right and left positions was accomplished by the rhyth-
mic strokes of the arm of a metronome.
For the first part of the work we used the galvanometer NIIF LGU (Sci-
entific - Research Institute of Physics, Leningrad State University) with a
sensitivity of 1.1 10-9 a, an internal resistance of 7800 ohms, a critical
resistance of 3020 ohms, and an oscillation period of 5.1 seconds. Through
experiments conducted on a series of sr'lutions (neutral, alkaline, and acid),
we succeeded in the attempt to obtain polarization curves whose curve charac-
teristics were not distinguishable from curves obtained with a mercury drop
cathode. This is sufficiently verified by the polarograms cited below.
The results of experiments to study the influence on polarograms of
the switching frequency of the electrodes permit it to be asserted that the
latter L.e., frequenc] has a rather narrow optimum which approaches in value
the velocity of dropping of mercury which is usually employed in polaro-
graphic analysis.
In Figure 2 are reproduced polarograms of an alkaline solution of lead
with a concentration of lc 10- N which were recorded for various velocities
of switching the electrodes: from 2.3 to 0.3 seconds for each switching.
It is not difficult to detect the general rule for the variation of these
curves where, with an increase of the frequency of switching, togethar with a
decrease of he period of oscillations, the current component which depends
linearly on the voltage increases, and the heights of the waves of electrolytic
reduction of the metals also increase.
We chose a switching period of the order of one second for each extreme
position of the switch.
The question of the influence of the surface dimensions of the small
electrodes on the polarization curves was considered for the present only
within the above-specified limits. It was shown that variation of the sur-
face area within these limits led only to a corresponding variation of the
strength of the current, but not to any variation of the character of the
polarogram. This is illustrated by Figure 3, in which are reproduced the
curves for lead and zinc in a 10% solution of Rochelle salt which were obtained
by using amalgamated platinum electrodes.
Curve I, corresponding to a lead concentration of(/72-lo-3 N, a zinc
concentration of v)7.10-3 N, and electrodes with a length of 6 mm and a diam-
eter of 0.5 mm, were recorded at a galvanometer sensitivity of'3.5/3020.
Curves II and III show the results of the electr-"lysis of the same solution
with another pair of electrodes of 0.3 mm diameter and v)1.5 mm.length. These
curves correspond to a 28/3020 galvanometer sensitivity, i.e., to obtain waves
approximating in amplitude those obtained with the first (large) i,sir of elec-
trodes, it was necessary to increase the sensitivity of the galvanometer eight
times.
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This demonstrates an increased possibility, compared with the method of
the mercury drop electrode, for the arbitrary choice of the strength of the
electrolytic current through a simple change of the surface area of the polar-
izable electrodes; this can be of interest from the point of view of the tech-
nical application of the method.
It is interesting to note that the current maxima characteristic of cer-
tain solutions which occur in electrolysis with the mercury drop cathode did
not appear in the work with the circuit described here; this is in agreement
with the new representations of tue theory of the nature of maxima auvanced by
A, N. Frumkin and Bruns (Acta Phys-Chim, URSS No 2, 1938 fIn Englis]).
The disadvantage of the method in the first stage of its development, in
comparison to the method of the mercury drop electrode, is the inferior defini-
tion of the development of the waves in the curves, which lowers the sensitiv-
ity of the analysis, particularly when some reducible components are present
in small concentrations in the solution.
The above is illustrated by the example shown in Figure 4, where there
are reproduced polarograms taken with a solution of 10% Rochelle salt which
contained copper, lead, cadmium, and zinc in concentrations of - 8.10-4 N with
the use of the described circuit of solid electrodes (curve I) and with a
mercury drop electrode (curve II).
For practical utilization of this method, it is necessary to further in-
vestigate and perfect it, and in particular to guarantee the possibility of
regulating the depolarizing current's density, the depolarization time of each
small electrode, and the time of its "rest" before it is connected for its
turn of polarization (note: the construction of a commutator which will satisfy
these conditions for a system of several solid electrodes can be successfully
accomplished in different variations of design).
Furthermore, the problem of the rational selection of electrode materials
for different electrolytic agents should be examined (we tested only platinum
and mercury).
Also, for any polarographic method of analysis the problem of compensation
for the current, which varies proportionally with the voltage, must be solved.
For this an ohmic resistance was connected in parallel with the electrolyzer,
the terminals g galvanometer! on the polarograph were short-circuited, and
the windings ofa differential galvanometer were connected to both parallel
branches of the circuit (electrolyzer and ohmic resistance). Synchronization
of the connection and disconnection of the electrolyzer and rheostat was accom-
plished by changing the double-pole switch to triple-pole, as shown in Figure
5 (note: it is evident in Figure 5 that this simple circuit not only permits
the ohmic resistance R to be connected to compensate for a linearly growing cur-
rent; in addition to R a second electrolytic cell with any composition of elec-
trolyte can be connected).
For recording the current a "Hartman and Braun" differential galvanometer
of type 172 B, with an internal resistance of 60 ohms, critical resistance of
400 ohms, half-period of oscillation of 4.5 seconds, and sensitivity of 75.10-10a
was used..,
An example of the compensation obtained through this circuit is shown in
the polarograms cited in Figure 6, where curves I and II represent a lead nitrate
solution with a concentration of 7.10-4 N, the polarograms being taken without
the use of compensation (at various sensitivities) with amalgamated platinum
small electrodes and a large mercury electrode. Curve III was obtained as a
result of connecting the compensation circuit.
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Curves IV and V represent the same solution and were taken with small and
large platinum electrodes, without and with compensation for the linear in-
crease of current, respectively.
Utilization of the proposed circuit permitted.the determination in in-
dividual cases of metal in concentrations down tocn 2.10- N.
In conclusion, we ought to devote some time to the direct determination
of cations of precious metals (note: the mercury drop electrode does not'
allow this possibility, for ions of metals more noble than mercury (Ag, Au)
are reduced by mercury itself; moreover, ions of mercury are also very diffi-
cult to locate polarographically by use of a mercury electrode).
The possibility of using electrodes of a more noble metal than those
which were being determined made this pr'-lem easily solvable. The experiment
for the polarographic determination of silver, gold, and mercury is illustrated
by Figures 7, 8, and 9.
Curve I in Figure 7.shows the polarogram taken with a 10% solution of
sodium nitrate, with a silver content of c/25?10 3 N and an HNO3 content of
10-1 N. Curve II corresponds to the same solution, to which is added silver
up to a concentration of about 10-2 N. Curve, III was taken following the
addition of silver up to c-1.7-10-2 N.
In Figure 8 are shown polarograms of gold.
Curve I corresponds to the original solution, containing 9 cc of a 10%
solution of potassium chloride and 1 cc of a 1% solution of gold chloride in
0.1 hydrochloric acid.
The other curves (II, III, IV, and V) were taken with the original solu-
tion after the addition of new portions of gold chloride.
Mercury also was determined satisfactorily with platinum electrodes, as
is illustrated by the examples of curves which are cited in Figure 9. The
first four of these correspond to the joint determination of mercury and lead
in a 5% solution of sodium mitrate. Curve V shows the results of the joint
determination of mercury, lead, and copper at ionic concentrations of.mercury
_10-2 N, copper v,5.10-3 N, and lead -)1.5-lo-2 N.
1. Solid metal electrodes were tested by using a circuit providing for
the periodic' depolarization of the surface area of the polarizable electrodes
by means of an electrochemical process.
2. Favorable results were obtained in the polarographic determination of
metals.
3. The proposed method of polarographic analysis can expand the area of
the application of this method significantly; in particular, it makes possible
direct polarographic determination of metals more noble than mercury, as well
as polarographic investigation of molten electrolytes.
4. The aim of further research should be the study of optimum conditions
of electrolysis to obtain the greatest reliability, accuracy, reproducibility,
and sensitivity from the method`.
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Figure 1. Principal
Circuit of Cathode
Polarization With Two
Small Solid Electrodes
Figure 2. Polarogram of a 0.01N Alkaline Solu-
tion of Pb at Various Velocities of Switching
the Electrodes
Figure 3. Curves for Pb and Zn in O.OlN Solution
of Rochelle Salt With the Use of Amalgamated Hg
Electrodes
Figure 4. Curves for Cu, Pb, Cd, and Zn in
10% Solution of Rochelle Salt
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Figure 5. Principal Compen-
sation Circuit of Cathode
Polarization
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Figure 6. Polarogram of Pb, Taken Without Com-
pensation for Current (curves I, II, IV), and
With Compensation for current (curves III) V)
Figure 7. Polarogram of 10% NaNO3 With
a Varied Content of Ag
d
Figure 8. Polarogram of Au in 10% Solution
KC1 + 0.1N HC1
Figure 9. Polarogram for Hg, Pb, and Cu in 5%
Solution of NaNO 3
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