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NEW EXPERIMENTAL METHODS FOR THE DROPPING MERCURY ELECTRODE

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Xerox University Microfilms
300 North Zeeb Road
A nn A rbor, M ichigan 48106
ld39°7
•G7
1940
•P4
*14
|Gr\Q7
Petras, John Francis.
\0* I ®j lAJ
New experimental methods for the
dropping mercury electrode...
New
York, 1940.
3p.1.,34 typewritten leaves, illus.,
tables,diagrs. 29cm.
Thesis (Ph.D.) - New York university,
Graduate school, 1940.
Bibliography: p.34.
Bound with this is a reprint of his
article A rapid method for traces of
metals by the
dropping mercury
electrode.
f
A54441
V
S:-.o!f List
Xerox University Microfilms,
Ann Arbor, Michigan 48106
THIS DISSERTATION HAS BEEN M IC R O FILM ED EXACTLY AS RECEIVED.
[R e p rin te d from th e J o u rn al of t h e A m erican C h e m ic a l Society,
60, 2990
(1938).]
[C o n t r ib u t io n f r o m t h e C h e m ic a l L a b o r a t o r ie s o f W a s h in g t o n S q u a r e C o l l e g e , N e w Y o r k U n i v e r s it y ]
A Rapid Method for Traces of Metals by the Dropping Mercury Electrode1
By
R a lp h
H.
M u lle r and J o h n
Introduction
In developing and testing the cathode ray tu b e
polarograph2 th e authors required som e means for
obtaining th e conventional Heyrovsky c u rren tpotential curves. I t is obvious t h a t these can be
obtained m anually and indeed the earliest studies
w ere made in this fashion. It was to relieve th e
tedium of th is procedure that Heyrovsky d e ­
veloped the autom atically recording polarograph.
T h e polarograph has th e further advantage of p ro ­
viding a perm anent record. On th e other hand,
th e “manual” curves m ay be obtained with rela­
tiv ely inexpensive and commonly available equip­
m en t. The m arked sym m etry of th e curves a t
once suggests a simple and ra p id increment
m ethod for determ ining th e concentration of a
given ion.1* T he object of this p ap er is to dem ­
onstrate the validity of th e increment method a n d
to illustrate its applicability.
Apparatus
I t is common knowledge th a t a potentiometer will de­
liver at its e. m . f. terminals the potential which is set on
th e dials. In our work a Leeds and N orthrup student(1) Presented before the Microchemical Division of the A merican
Chem ical Society, Milwaukee, W isconsin, M eeting, September, 1938.
(2) R. H. M uller, R . L. C arm an , M. E. D roz and J. F. P e tra s,
I n i , E x t. Chem., A n a l. Ed., 10, 339 (1938).
(2a) After this p ap er was su b m itted for publication the a u th o rs
learn ed of similar w ork by Petering and Daniels in which the in cre­
m e n t technique h a s been applied to the micro-analysis of oxygen.
T h e ir application undoubtedly precedes this contribution, and we
re g a rd our work a s a general confirmation of th e validity of th e in ­
crem en t principle. T he senior a u th o r is indebted to Professor D a n i­
els for helpful discussion and exchange of opinions a t the Milwaukee
m eeting and subsequently a t his laboratory in M adison.
F.
P e tra s
type potentiometer was used to deliver the desired poten­
tials. The working current of the potentiometer was bal­
anced against a standard cell in the usual manner. The
e. m. f. terminals were connected to the electrode vessel in
series w ith a wall-type galvanometer L and N Type P, 103
megohm sensitivity, resistance 126 ohms, period 8.9 sec.
The la tte r was used in conjunction with an Ayrton shunt
carefully adjusted to provide the critical damping resist­
ance. The suspension was turned so that readings could
be taken over more than half the scale length. The entire
assembly was calibrated for linearity of response and used
over th a t range. The electrode was of the type commonly
used in polarographic work,’ and consisted of a small
Erlenmeyer flask w ith a platinum wire inseal for making
connection with the mercury anode, and a bubbler inseal
for flushing the contents of the vessel with hydrogen. The
capillaries for the dropping mercury cathode were hand
drawn from 1-mm. capillary tubing. They were graded
for suitable lumen by examination under a low power
microscope fitted with a micrometer ocular. The vessel
was also provided with a salt bridge communicating with a
saturated calomel electrode. In this way the anode poten­
tial could be measured. A switching arrangement en­
abled th e operator to check the anode potential with the
potentiometer. The mercury dropping rate was con­
trolled b y the pressure unit previously described.* It was
found to be far more convenient and flexible.
Solutions
The solutions used in this work were prepared from re­
agent quality chemicals without further purification.
Eastman purified de-ashed gelatin was added to all solu­
tions to give a final concentration of 0.2%. A wide
choice of addition agents is feasible. In routine work,
(3)
J . Heyrovsky, in W. B5ttger, “ Physikalische M etboden der
chem ischen Analyse," Akademische Verlagsgesellschaft m. b. H.,
Leipzig, 1935; Hohn, "Chemische Analysen m it dem Polarograpfaen," V erlag von Julius Springer, Berlin, 1937.
Dec., 1938
T
races o f
M
etals by th e
common glue has been found satisfactory by some in­
vestigators. A fairly complete list of suitable supporting
solutions is given in H ohn’s monograph. The indifferent
electrolyte which was used in each case is indicated in the
appropriate place. Oxygen was removed from all solu­
tions just before use by bubbling pure hydrogen through
the vessel. The formation of persistent bubbles due to
the gelatin content was very annoying, but it was elimi­
nated completely by the addition of a trace of caprylic
alcohol. We were agreeably surprised to note th at neither
the dropping rate nor values of the potentials were ad­
versely affected.
E xperim ental R esults
A typical current-voltage curve is shown in
Fig. 1. In this case equal am ounts of cadmium
D
M
r o p p in g
ercury
E lectrode
2991
subtracted, yielding Cd = —0.64 v., and Zn =
—1.07 v.
Figure 2 shows a family of curves obtained in
this manner for cadmium a t various concentra­
tions. I t is custom ary in polarographic work to
draw the best straight line through each plateau
and then estim ate the difference in height (AI).
Alternative schemes for estim ating the correct
wave height are discussed in the above mono­
graphs and in th e paper by Borcherdt, Meloche
and Adkins.4 D ue to th e marked sym m etry of
the curves, it would seem th a t the current values
obtained for tw o potentials more or less equidistant
from the characteristic “ Halbwellen” potential
would yield a A / value which is equally reliable.
12
Zn
10
8
6
s 12
4
[.
2
0
0
0.4
1.2
0.8
1.6
2.0
Potential, volts.
Fig. 1.—0.001 M Zn(NOi),, 0.001 M Cd(NO,)Sp
0.1 A fKCl, 0.2% gelatin.
and zinc nitrates were used with 0.1 M potassium
chloride as th e indifferent electrolyte. A t each
applied potential the galvanom eter deflections are
pulsating due to the dropping of th e mercury a t
the cathode. The recorded values represent the
maximum “throw ” or excursion of th e galvanome­
ter. These are highly reproducible and it was
rarely necessary to observe more than tw o or
three “throws.” The “ Halbwellen” potential, de­
fined as th a t potential o n the curve corresponding
to one-half th e distance between th e horizontal
plateaus, is indicated in Fig. 1, for each ion. From
each potential the anode correction of 0.04 v. was
0
0.4
0.8
1.2
Potential, volts.
Fig. 2.—Concn. CdCl,: A, 30 X 10“*
M; B, 27 X 10~* M; C, 23 X 10~» M;
D, 19 X 10-* M; E, 15 X 10“* M ; F,
11 X 10-* M ; G, 7.5 X 1 0 M ; H,
4.0 X 10-* M . All 0.1 M BaCl;, 0.2%
gelatin.
A cross plot of Fig. 2 is shown in Fig. 3. By
inspection it w as decided to select 0.6 and 0.8 v.
For each concentration of cadmium th e difference
in current obtained a t 0.8 an d 0.6 v. was interpo­
lated. These AI values were plotted against the
(4)
n a l,
G . P. B orcherdt, V. W. M eloche end H. Adkins, T h is J o u r ­
09 2171 (1937).
2992
R a lp h
H.
M O lle r a n d Jo h n
10
/
/
/
■3 6
/
/
/
/
//
0.8
1.6
2.4
32
Concn. Cd, M X 10*.
Fig. 3.—Cross plot of d ata in Fig. 2, il­
lustrating linearity obtained b y the incre­
m ent method.
0
concentration of cadmium. W ith one exception
th e points lie closely on a straig h t line. This
represents the w orst condition for checking the
relationship, in th a t considerable tim e elapsed in
taking th e whole family of curves. Succeeding
runs w ith th e simplified technique of merely meas­
uring th e respective currents for applied poten­
tials of 0.6 and 0.8 v., amply confirmed this point.
A typical example is shown in Fig. 4. In this
and all subsequent runs, a titra tio n procedure was
used to change th e concentration. Specifically
(Fig. 4), th e electrolyte contained 0.1 M barium
chloride as the indifferent dectrolyte, 0.2% gela40
>
32
(Cl
*
3 24
/
u 16
V
/
/ X
0
0
X
x
Zn
LX
s
4
8
12
16
Concn. i f X 10*.
Fig. 4.—U pper curve: 0.01 M CdCli in
0.1 M BaCl* + 0 2 % gelatin titrated into
0.1 i f BaCli + 0 2 % gelatin. Lower
curve: 0.01 i f ZnCl, in 1.0 I f KOH +
0.2% gelatin titrated into 1.0 i f KOH +
0.2% gelatin.
F.
Vol. 60
P e tra s
tin and to it were added from a m icroburet suc­
cessive portions of 0.01 M cadmium chloride in
0.1 M barium chloride containing 0.2% gelatin.
T he final concentrations of cadm ium ion were cor­
rected for th e small change in to ta l volume.
The m ethod is quite satisfactory for traces of
one ion in th e presence of a large am ount of other
ions, provided the la tte r are reduced a t higher po­
tentials, and further th a t th e interval betw een the
respective potentials is great enough. I n general
th e same limitations th a t apply to polarographic
m ethods apply here, and certain cases can only be
treated after preliminary separation or a fte r con­
version to suitable complex ions, etc.
32
/
24
<
If X
i 16
V
8
0X
X
0
4
8
12
16
Concn. Cd, i f X 10*.
Fig. 6.—Traces of Cd in a large amount
of zinc: 0.01 i f Cd(NO»)» in 0.1 i f
ZnCh + 0.2% gelatin titrated into 0.1 i f
ZnCli + 0.2% gelatin.
Figure 5 illustrates th e results for small am ounts
of cadmium in the presence of a large b u t constant
am ount of zinc. I t will b e observed th a t the
slopes for th e Al-concn. curves for C d ++ ion in
Fig. 4 and Fig. 5 are quite different. T h e actual
slope depends upon the size of the m ercury drop,
th e dropping rate, th e concentration a n d nature
of th e indifferent electrolyte, and the galvanome­
te r sensitivity. In a given ru n these factors are
constant. T o the extent th a t they m ight be re­
produced in subsequent runs, th e slopes would be
correspondingly similar. F o r routine w ork this
would seem to be a source of great trouble and in­
convenience. This is a general lim itation of all
existing polarographic m ethods; they all assume
th a t a preliminary calibration has been made
under conditions closely approxim ating th e in­
tended analysis.
I t is always possible, however, to include within
th e solution of the indifferent electrolyte a suitable
“indicator” ion in known am ount, preferably one
Dec., 1938
T
races o f
M
etals by th e
D
r o p p in g
M
ercury
E
lectrode
2993
which is n o t likely to be present in th e “unknown.”
T he indicator ion m ay then be used to evaluate the
prevailing constants of th e apparatus, thus fur­
nishing a factor for th e observed slopes.
Figure 6 shows results obtained for lead in
strong alkaline solution. A complete curve for
lead is shown merely to illustrate th e choice of the
tw o symmetric potentials which were selected for
th e analysis by th e increm ent m ethod. T he ad­
joining curve shows th e AT values as a function of
lead concentration.
0
4
8
12
16
Concn. Pb, M X 104.
Fig. 7.—Traces of Pb in a large amount
of zinc (alkaline solution): 0.01 M Pb(NO,), + 0.1 M Zn(NO»)» in 1.0 M KOH
-I- 0.2% gelatin titrated into 0.1 M
Zn(NO,)t in 1.0 M KOH + 0.2% gelatin.
f
40
A
.
v/
24
16
8
V
/
/
'
0
0
0.4
0.8
1.2
1.6
Concn. Pb, M X 104.
Fig. 6.—Upper curve:
typical currentvoltage curve for lead in alkaline solution.
Lower curve: increment method, 0.01 M
Pb(NO»)i in 1.0 M KOH + 0.2% gelatin
titrated into 1.0 M KOH
0.2% gelatin.
Figure 4 is the increm ental plot as a function of
zinc concentration in alkaline solution an d Fig. 7
shows th e behavior of small am ounts of lead in the
presence of a large b u t constant am ount of zinc,
again in alkaline solution.
D iscussion
The increment m ethod which h as been sug­
gested for the evaluation of current-potential
curves for the dropping m ercury electrode has
been shown to be reliable for three commonly oc­
curring ions and m ixtures of th e sam e in neutral
and alkaline solutions. In principle it is exactly
similar to th e practice of evaluating curves which
have been recorded on a polarograph. I t is ex­
trem ely simple and rapid and m erely assumes a
reasonable degree of sym m etry in th e curve. Its
applicability can be ascertained very quickly in any
case. For cases in which th e deposition potentials
are too dose, difficulties will be encountered to
the same extent th a t they are in the conventional
method. T he use of gelatin o r related substances,
and the de-oxygenation by a stream of hydrogen
are essential to success; the well-defined plateaus
are largely dependent upon these factors.
For anyone slightly acquainted with electrical
instrum ents, it will be apparent th a t a good po­
tentiom eter is not essential for this method. Any
simple voltage divider with suitable means for
adding and subtracting the required v .’s will suf­
fice. In this general investigation we retained
the more d e g a n t arrangem ent because of its
greater convenience and flexibility.
Sum m ary
1. C urrent-potential curves m ay be obtained
from the dropping m ercury electrode with very
simple equipment.
2. The m arked sym m etry of these curves sug­
gests a simple increment m ethod in which the
change in current is noted for tw o applied poten­
tials more or less equidistant from the character­
istic “H albw dlen" potential. The current incre­
m ents are a linear function of the concentration
of the given ion.
3. The presence of other ions does n o t interfere
w ith this relationship to any greater extent than
it does with conventional polarographic methods.
4. The m ethod has been illustrated w ith lead,
zinc and cadmium ions, and pairs of these in neu­
tra l and alkaline solution.
N e w Y ork, N . Y .
R e c e i v e d A u g u s t 19, 1938
Reprinted from Analytical Edition, INDUSTRIAL AND ENGINEERING CHEMISTRY, Vol. 10, Page 339, June 15, 1938
The Cathode Ray-Tube Polarograph
T heory o f M ethod
R. H. MULLER, R. L. GARMAN, M. E. DROZ, a n d J . PETRAS
Chem ical Laboratories of W ashington Square College, New York University, New York, N. Y.
HE polarograph as developed by Heyrovsky and his co­
as performance of the record, etc. I t would seem natural to
workers is an instrument well known to electrochemists
utilize the cathode ray oscillograph for this purpose, but in
and analysts. The theory and applications have been sum­practice a number of difficulties arise. Oscillograph practice
marized in several monographs (I, 2). The recording of
requires rapid recurrence of the phenomenon if a persistent
current-potential curves of a dropping mercury electrode may
stationary image is desired. I t is true that transient images
be accomplished in a number of ways. Heyrovsky gives
can be photographed, but this procedure would nullify the
adequate reasons for preferring the photographic method, such
advantage of a continuous picture of what is going on. If
we attempt to sweep through the range of
potentials very rapidly in order to produce a
persistent stationary pattern, the question arises
whether the electrode equilibria can keep pace
with the rapidly changing potentials.
The authors have found a solution to this
problem and the instrument based on this
method yields values identical with those based
upon the conventional Heyrovsky method.
T
I
Theory
Let curve OAHBC of Figure 1 represent an ideal­
ized Heyrovsky polarogram for a certain ion. The
potential, V, corresponding to point H, is the
HaUneeUenpotential and represents a characteristic
identifying value, for the given ion. Now imagine
a small sinusoidal alternating potential of peak
value, A V , applied to series with the main poten­
tial, V. The current, I, will now vary about the
mean value, H, to produce a wave, S, of the same
wave form and frequency, but with an amplitude
which depends upon the steepness of curve AHB.
If the main direct current potential, V, is now
shifted the sine wave, S, will become distorted at
its upper or lower portion because of intersection
with the nonlinear portions of the curve at B or
A. If this curve, S, is continuously viewed on an
oscillograph screen it will be almost perfectly sinu­
soidal ana undistorted when and only when V has
F ig u r e 1
CATHODE
RAY
OSCILLOG RA PH
| u
1
1
i
j
c
u
u
PB
R,'
aV w vat-a .5 v .-»
no v.
A.C.
F ig u r e 2 .
C i r c u i t (L e t t ) a n d D ia g r a m o r A p p a r a t u s ( R ig h t )
340
INDUSTRIAL AND ENGINEERING CHEMISTRY
VOL. 10. NO. 6
a value corresponding to the mid-point of the current-potential
curve (at JET). Conversely, the appearance of such undistorted
waves, as V is varied from zero to the maximum value of deposi­
tion potentials, will serve to detect and identify the characteristic
potentials.
The Instrument
The circuit is shown in Figure 2, left. Battery B supplies the
potentials through regulating resistor R, and voltage divider Rt.
The voltmeter, V, indicates the applied potential The small
alternating potential in series with tne direct current potential is
supplied by step-down transformer T, and voltage divider fi«.
The lead to the dropping mercury cathode passes through the
high-gain, low primary-impedance transformer, Tt. The sec­
ondary of this transformer is connected to the vertical deflector
plates of the cathode ray oscillograph. If the oscillograph is not
provided with a built-in amplifier or one of sufficient gain (3000
to 6000 X) it must be preceded by a voltage amplifier stage. The
horizontal deflector plates are driven by the usual sweep circuit
and in most cases means are provided for locking in the sweep
with the phenomenon under investigation (synchronizing con­
trol).
Tne authors have eliminated the customary leveling bulb for
supplying mercury to the dropping electrode in the interest of
compactness and convenience of manipulation and to facilitate
careful electrical shielding of the electrode assembly.
Figure 2, right, shows a simple arrangement of pressure bottle
PB, rubber bulb B, and two-way stopcock S with a micro bubble
regulator, R. Manometer M gives a rough indication of the
driving air pressure. Actually, the rate of dropping of mercury
is the best criterion of satisfactory operation, ana this is quickly
adjusted by means of the stopcock by-pass. Since very little
mercury is used, the air reservoir requires very infrequent at­
tention.
Figure 3 shows a photograph of the instrument. The oscil­
lograph is on the right. The main case on the left contains the
circuit and controls. The vol tmeter indicates the critical direct
current potentials. The left hand dial controls the voltage
divider, Rt. The right-hand dial, Rt, governs the magnitude of
the alternating current potential. Toggle switches are provided
for the battery and alternating current supply. Tne small
copper case mounted on the right side of the instrument contains
the electrode assembly and can be tightly closed by means of a
copper door. The electrode connections pass directly through
the wall through insulated connectors (‘‘banana plug” type).
The case is grounded during operation. Connection to tne os­
cillograph is made through shielded cable. Reasonably careful
shielding and the absence of loose, rambling wires are essential
for satisfactory operation.
Operation
A typical polarogram as obtained by this instrument is
shown in Figure 4. In this case the solution contained a
small amount of cadmium ion (5 mg.), 0.002 M. At an ap­
plied potential of 0.63 volt the oscillograph pattern is as shown
in a. Potentials slightly less than this value yield the dis­
torted curve, 6, whereas at slightly higher potentials another
distorted curve, c, results. This behavior is explained in the
Fiotraa 3
F racas
4.
T y p ic a l P o la ro g ra m
JUNE IS, 1938
ANALYTICAL EDITION
discussion of Figure 1. On a complete analysis the operator
merely increases the potential, V, manually from zero to the
maximum and notes the potentials at which symmetrical
waves appear. The process can be repeated as often as de­
sired. For feeble curves (traces of ion) the gain control may
be stepped up in order to miss none. Under these circum­
stances the maxima due to large amounts of other ions will
produce high deflections, beyond the edge of the screen, but
the instrument is not damaged as a delicate galvanometer
would be.
The entire pattern disappears when a mercury droplet
falls from the capillary. A new curve appears almost im­
mediately, and the momentary interruption is not disturbing,
inasmuch as the general technic requires fairly slow dropping
rates.
The observed potentials are very reproducible and vary by
only a few millivolts—0.627 to 0.629 in the above case. Fur­
thermore they are identical with the values obtained in the
conventional way—with a voltage divider and galvanometer.
In all cases in which the new instrument was compared
with the “manual” method it was absolutely necessary to cor­
rect the observed potentials for the anode potential as meas­
ured against the solution with a calomel electrode in the con­
ventional way. Authorities (1, 2) agree that this is necessary
to obtain the standard value for each ion as recorded in the
literature. Thus for zinc ion (0.001 M) the authors observed
a value of —1.110 volts, and the anode potential correction
was 0.041 volt yielding —1.069 volts for the Hcdbwellenpotential. The accepted value is —1.06 volts.
Discussion
So far no mention has been made of the quantitative as­
pects of the instrument. Reference to Figure 1 will show that
the final deflection of the cathode ray beam at the Halbwellenpotentiai depends upon the gain of the amplifier, the value of
341
V, and the height of the “Heyrovsky curve” for the particu­
lar ion under observation. The gain of the amplifier may
be held constant and AF adjusted to some predetermined
value. Investigations are in progress for the determination
of suitable values of the voltage under various conditions of
operation, so that quantitative estimation may be accom­
plished with the instrument.
The complete instrument, including the oscillograph but
not labor, costs $150.
Summary
Current voltage curves taken with an oscillograph using a
small series alternating current potential yield patterns which
are interpretable on the basis of the conventional Heyrovsky
method.
The polarograms are viewed continuously and require no
photographing or recording.
The actual identification is in terms of the same potentials
used by the classical methods.
The introduction of the small alternating current compo­
nent does not give rise to any complications; the observed
values are the same as those obtained with direct current.
The analysis can be repeated indefinitely and the results
are continuously visible to the operator.
Sensitivity control is not hampered by possible damage to
the recording instrument.
Literature Cited
(1) Heyrovsky, J., in W. Bottger, “Physikalische Methoden der
chemischen Analyse/* Leipiig, Akademiache Verlag, 1935.
(2) Hohn, “ Chemische Analyaen mit dem Polarographen/’ Berlin,
Julius Springer, 1937.
R bckiykd M ar oh 30,1938. Presented by the senior author a t the New York
Microchemical Society November 19, 1937; th e N orth Jersey Seotion,
American Chemical Society, February 14, 1938; and th e M etropolitan
Section, Electrochemical Society, February 21.1938.
P rutted in U. S. A.
L ib r a r y
N . Y. U m y?
NEW EXPERIMENTAL METHODS
for the
DROPPING MERCURY ELECTRODE
John Francis Petras, A.B*
Submitted In Partial Fulfillment of the Requirements
for the Degree of Doctor of Philosophy
at New York University
April 1940
Acknowledgment
The author wishes to express his sincere thanks and
appreciation to Professor Ralph H. Mttller for the
suggestion and direction of this research.
vi o 4 \ ?
TABLE OF CONTENTS
Page
1
PURPOSE
PART I
INTRODUCTION
1
APPARATUS
3
SOLUTIONS
5
RESULTS
System One: Manual curve for cadmium and sine.
6
System Two: Family of cadmium curves*
7
System Three: a) Lead in baslo solution by
Increment method*
8
b) Zinc in basie solution by
Increment method*
9
System Four: a) Traces of cadmium in a large
amount of sine*
b) Traces of lead in a large
amount of sine*
9
10
System Five: a) Copper* cadmium and sine with
eopper as "pilot" Ion*
10
b) Copper ., cadmium and sine with
sine as "pilot" ion*
11
PART II
INTRODUCTION
12
APPARATUS
12
RESULTS
System One:
System Two:
Copper* bismuth* lead* cadmium and
sine as tartrates*
14
Half wave potentials of thallous
thallium using the three types of
calomel cells*
15
Page
System Three* Constancy of half wave potential
with ooneentratlon using cadmium.
System Four:
Oxygen in solution hy the Increment
method.
16
17
PART III
INTRODUCTION
18
THEORY OF METHOD
18
APPARATUS
19
PROCEDURE
20
RESULTS
System One*
Half wave potential of cadmium.
22
System Two*
Half wave potential for lead,
oadmlum and sine in a mixture of
the three.
23
System Three* Lead and cadmium as tartrates.
26
Thallous thallium in neutral solution 28
System Fours
System Five*
Sensitivity of the method using
cadmium.
29
Trace of cadmium In a large amount
of oopper.
30
SUMMARY
32
BIBLIOGRAPHY
34
NEW EXPERIMENTAL METHODS
for the
DROPPING MERCURY ELECTRODE
PURPOSE
The purpose of this work was twofold*
1.) To investigate the possibility of a simple and
rapid increment method for the quantitative interpretation
of current-voltage curves obtained with the dropping mercury
electrode*
2.) To develop a new electrical method for the determi­
nation of the characteristic half-wave potentials obtained
from the above curves*
PART I
INTRODUCTION
The electrolysis of solutions containing electroreducible or electro&xidizable substances in a cell, in which
one electrode consists of mercury falling slowly in small
drops from a capillary, was invented by Jaroslav Heyrovsky
in 1922 (1)*
In 1925 Heyrovsky and Shlkata (2) developed
an Instrument, the polarograph, which takes current-voltage
ourves, wpolarograms", automatically and records them on
photographic film.
As most chemists know, in the intervening eighteen
years, it has been shown by many workers that these currentvoltage curves, when obtained under appropriate conditions,
will serve for the identification and quantitative estimation
of a large number Of Inorganic and organic substances*
De­
spite the many assertions to the contrary it is not to be
assumed that the subject rests on an insecure theoretical
foundation*
Equations have been derived whloh quantitatively
predict the identifying potentials and the magnitude of the
diffusion currents which two factors are the sole criteria
of qualitative identification and quantitative determination*
This is perhaps sufficient Justification for a method whioh
has proven Itself emminently practical in analytical chemistry*
While there are some four hundred and fifty papers
published on this method of analysis we find that quanti­
tative analysis has been neglected with emphasis on the
proof of reduction or qualitative detection of a great va­
riety of substances*
The notion has also prevailed that
quantitative analysis necessitates a polarograph*
This is
nicely refuted by the recent appearance of the simple ar­
rangement of Petering and Daniels (3) who utilise two heavyduty cells of definite potential and a galvanometer and that
of Kolthoff and Llngane (4) who make use of ordinary potentiometrio equipment*
In the present work, standard laboratory equipment was
used in conjunction with a simple, rapid Increment technique
for the quantitative interpretation of current-voltage curves
eliminating thereby the use of a polarograph and obviating,
moreover, the necessity for a complete manually recorded
curve,
APPARATUS
Figure 1 shows the principle of the circuit.
Since the
currents obtained in this method of electrolysis are of the
order of microamperes, indicating an effective resistance of
one megohm, a Leeds and Northrup, student-type potentiometer,
E, was used to deliver at its E.M.F. terminals the potential
which is set on the dials.
The working current of the po­
tentiometer was balanced against the Weston standard cell, D,
by thePoggendorf method through resistances A and B.
The
currents were measured by a Leeds and Northrup, Type P, wall
galvanometer, 103 megohm sensitivity, internal resistance 126
pihms, period 8.9 seconds and a critical damping resistance of
30,000 ohms.
The latter was used in conjunction with a shunt
H of two Leeds and Northrup, 4 dial precision resistance boxes
(9999 ohms),
and R£*
The total resistance of this shunt
was kept constant at 500 ohms at all times.
The latter value
was chosen as most suitable from the standpoint of convenience
of measurement.
With this shunting arrangement the sensi­
tivity of the galvanometer was computed from the resistance
ratios.
The suspension of the galvanometer was turned so that
-
3-
readings could be taken over more than half the scale
length.
The entire assembly was calibrated for linearity
of response and used over that range. At each applied po­
tential the galvanometer deflections are pulsating due to
the dropping of the mercury at the oathode.
The reoorded
values represent the maximam "throw" or excursion of the
galvanometer.
These are highly reproducible and that value
was selected where three readings agreed exactly.
Figure 2 is a schematic diagram of the electrode as­
sembly which was that of the type commonly used in polaro­
graphic work (1).
It consisted of a 125 cc. Erlenmeyer
flask with a platinum wire inseal, C, for making connection
with the mercury pool, A, serving as anode, and a bubbler
inseal D, for the dual purpose of flushing the contents of
the flask with hydrogen and stirring the electrolyte after
successive additions of solution from a 10 ml. microburette,
H.
In the Interest of convenience of manipulation, the
customary leveling bulb for supplying mercury to the dropping
electrode was replaced by the pressure bottle PB of two and
one half liter capacity, rubber bulb B, and a two-way stop­
cock S, with a micro bubble regulator R.
Manometer, M, with
a millimeter scale gave an indication of the driving air
pressure.
To obtain a strict linear relation between the
diffusion current and the concentration of a given reducible
substance, the time of formation of eaoh mercury drop, i.e.,
the drop-rate, should be about three to six seconds.
-
4-
The air
pressure was quickly adjusted to give the desired drop-rate
by means of a by-pass stopcock S, when the dropping electrode
was in the electrolyte.
Since very little mercury is used,
the air reservoir required infrequent attention.
The capil­
laries were hand drawn from commercial thermometer tubing of
circular bore as described by Heyrovsky (5) and graded for
suitable lumen by examination under a low power microscope
fitted with a micrometer ocular using axial illumination.
Whenever the value of the anode potential was desired, a salt
bridge, filled with the same solution as in the cell and
communicating with a saturated calomel electrode was used.
Solutions:
The solutions used in this work were prepared from
reagent quality chemicals.
In all cases the maximum amount
of electroreducible impurities which could be present were
a thousand times smaller than the detectable limit using
this method.
In all cases the solutions oontalned Eastman,
purified de-ashed gelatin to give a final concentration of
0,2% (6 ).
The nature of the indifferent electrolyte in a
concentration of 0.1 molar is indicated in the appropriate
place since it was necessarily different depending upon the
system studied.
Because oxygen is readily reduced at the
dropping electrode (7) and interferes with the currentvoltage curves of other substances, it is necessary to re­
move dissolved air from the solution to be electrolysed by
flushing with an inert gas before electrolysis.
In this
work pure electrolytic hydrogen from a tank was bubbled
through the solution, fifteen to thirty minutes usually
being sufficient.
The gas stream was stopped before e-
lectrolysis since its stirring effect causes irregular
fluctuations in the current.
The passage of hydrogen
caused persistent bubbles to be formed due to the gelatin
content but this effect was completely eliminated by the
addition of a trace of normal capryllc alcohol.
RESULTS
System 1.
A typical complete manually recorded current-voltage
curve is shown in Figure 3. The 50 ml. of solution con­
tained gelatin as a maximum suppressant and 0.1 molar KC1
as Indifferent electrolyte.
The metallic ions, cadmium and
zinc were present as nitrates to the extent of 0.0010 molar.
The galvanometer deflections which are a measure of the dif­
fusion current are plotted as ordinates and the applied
E.M.F. as abscissae.
throughout this work.
This method was used in all curves
The half wave potential, defined as
that potential on the curve corresponding to one-half the
distance between the horizontal plateaus (8 ), is indicated
for both ions.
From each half wave potential the anode
correction of 0.04 volts, referred to a 0.1 normal calomel
electrode, was subtracted (1) giving Cd** * -0.64 volts
and 2n++ a
-1.07 volts.
The accepted values are -0.63 and
-1.06 volts respectively.
-6 -
System 2*
The basis of quantitative polarography is the fact that
the diffusion ourrent is directly proportional to the concen­
tration of the electroreduoible substance*
This is illus­
trated by the family of curves for cadmium at various concen­
trations in Figure 4*
The solution was 0*1 molar with respect to Ba&2 with
gelatin as maximum suppressant*
It was deoxygenated by passing
hydrogen through it for twenty minutes*
To this was added*
from a 10 ml* microburette* a deoxygenated solution containing
0*010 molar CdCl2 * 0*1 molar BaClg and gelatin*
Stirring was
effected after each addition by bubbling hydrogen for one
minute* after which a complete curve was obtained*
A plot of the "diffusion current" against concentration
gives a straight line*
It is customary in polarographic work
to obtain the diffusion current in the following way;
the
best straight line is drawn through each plateau and the
difference in height is estimated*
Obviously this method
requires as many curves as there are concentrations*
However*
the marked symmetry of the curves at once suggest that the
current values obtained for two potentials more or less equi­
distant from the characteristic half wave potential would
yield a "diffusion current" value which is equally reliable*
This is Illustrated by the cross-plot of the curves of Figure
4 in Figure 5* By inspection it was decided to select -0*600
and -0*800 volts and for each concentration of cadmium the
-
7-
difference In current In terms of galvanometer deflections
obtained at -0.800 and -0.600 was taken.
These values, which
represent an Increment proportional to the cadmium concen­
tration, were plotted against the oonoentratlon of cadmium.
With one exception the points lie closely on a straight line,
indicating a simple and rapid increment method for determin­
ing the concentration of a given electroreduoible metallic
ion, and obviating the necessity of a complete curve for each
concentration.
Figure 6 shows the results obtained for the same system
as above but using the increment technique directly.
The re-
deflections for the applied potentials of -0.6 and -0.8 volte
were measured and the increments plotted against concentration
of cadmium, whose final concentrations were oorrected for the
small change in total volume.
System 5.
The choice of the symmetric potentials must, however, be
done from a complete curve for the particular substance because
the spread of these potentials will depend upon the shape of
the curve.
This is strikingly Illustrated in the ease where
successive portions of 0.0100 molar Pb(H03)g in 1 molar KOH
containing 0.2£ gelatin were added to 50 ml. of 1 molar KOH
as indifferent electrolyte and the same concentration of gelatin.
Figure 7 shows the complete manually reoorded curve for ap­
proximately 0.001 molar lead.
This curve served as the basis
for the oholee of the two symmetric potentials of -0.400 and
« 8-
•0*900 volts*
Having determined the tvo potentials the Incre­
ment method was than used on the ahove system.
Figure 8 is
the Incremental plot for lead In strongly alkaline solution
as a function of the lead concentration*
The same Investigation was carried out for slno In
strongly alkaline solution over a somewhat larger range of
concentration*
To 60 ml* of 1 molar KOH containing 0*2#
gelatin were added,from a microburette, successive portions
of 0*0100 molar ZnClg In 1 molar KOH containing 0*2£ gelatin*
Figure 9 shows the Incremental plot as a function of the sine
concentration*
As before, In the case of lead, a complete
curve for sine in approximately 0*001 molar concentration was
taken in order to determine the two symmetrle potentials of
•1*000 and -1.500 volts*
System 4*
The increment method is satisfactory for traces of one
Ion in the presence of a larger amount of other ions provided
the latter are reduced at higher potentials*
This was illus­
trated for a system which contained small amounts of cadmium
in the presence of a larger but constant amount of slno*
Figure 10 is the Incremental plot of cadmium as a function of
the cadmium concentration*
Specifically, the Indifferent e-
leetrolyte was 0*1 molar ZnClg with gelatin Into which, from
a microburette, were added successive portions of 0*0100 molar
CdtHOjJg In 0*1 molar ZnClg with gelatin*
The two symmetric
potentials for cadmium were again -0*600 and -0*800 volts,
-
9-
obtained by Inspection from a complete manually recorded
curve*
The same procedure was followed In the case of traces
of lead In a large amount of sine*
In this Instance, uti­
lizing the titration procedure successive portions of 0*0100
molar PblNO^g in 0*1 molar Zn(103)2 made 1 molar with re­
spect to KOH and 0.2j£ gelatin were added to a solution con­
taining 0*1 molar Zn(N03)g in 1 molar KOH and gelatin*
Figure 11 shows the incremental plot for lead as a function
of the lead concentration*
System 6*
A further simplification of the increment technique
suggested itself Involving the use of a calibrating or "pilot"
ion*
Since the "diffusion current" is directly proportional
to the concentration of the electroreduclble ion, when two
electroreduclble ions with sufficiently different half wave
potentials are present, It should be possible to keep the
concentration of one constant (the "pilot" ion) while vary­
ing the concentration of the other (the unknown ion)* A
plot of the ratio of the diffusion currents of unknown ion
to "pilot" ion as a function of the concentration of unknown
ion should give & straight line*
Two studies were made on a
system containing the three electroreduclble ions, Cu++, Cd++
and Zn++*
In the first study Zinc was used as the "pilot" ion* The
solution in the eleotrolysing vessel contained 50 ml* of 0*1
-
10-
molar RaROg with 0.2# gelatin and 0*00100 molar with respect
to Zn(H03 )2 * Sato this was added, from a mloroburette, a
solution of 0*1 molar NaNOg also oontaining slno, eadmlmnm
and copper nitrates in concentrations of 0*00100 molar, 0*100
molar and 0.100 molar respectively.
Readings were taken at
four potentials, -0.05Q, -0.550, -1.100 and -1*650 volts re­
spectively.
The choice of these potentials was made from an
examination of a complete manually obtained curve shown in
Figure 12*
Curves B and D on Figure 13 are a plot of the
ratios of cadmium-aino and copper-sine as a function of the
concentration of cadmium and copper.
In the second study copper was made the "pilot” ion.
The solution in the electrolysing vessel contained 50 ml* of
0*1 molar RaROg with 0*2£ gelatin and was 0*00100 molar with
respect to Cu(803)2 * 3fcto this was added, from a mloroburette,
a solution oontaining 0.1 molar RftROg, 0.00100 molar Cu(803)2 ,
0.100 molar Cd(H0g)2 and 0.100 molar Zn(H03)2 * The readings
were taken at the same four applied potentials as in the previ­
ous study.
Curves A and C of Figure 13 are a plot of the
ratios of cadmium-copper and zinc-copper as a function of the
concentrations of cadmium and zinc*
In each case the under­
scored species represents the "pilot” ion.
The curves are
displaced along the ordinate for the sake of clarity.
-
11-
PART II
INTRODUCTION
The studies made with standard and generally available
equipment show the relative ease and simplicity of obtaining
polarographic curves. Upon the publication of the increment
technique we were invited by the Fisher Scientific Company
to design a compact and portable Instrument whioh would be
suitable for chemical analysis utilising the increment and
"pilot" ion technique.
Their instrument, called the
"ELECDROPODB", embodies the following features: a eompaot
assembly of the necessary components which are suitable for the
manual recording of current-voltage curves as well as the
Increment and "pilot" ion technique.
APPARATUS
The Instrument is shown in Figure 14.
It oonslsts es­
sentially of a simple voltage divider, a galvanometer and
the dropping electrode assembly.
Two dry cells supply the
potentials and a simple resistor network provides potentials
0 - 1 volt, 1 - 2 volts, 2 - 3 volts.
A uniform slide wire
resistor marked "Potential", subdivides each of these ranges
making it thus possible to read the potentials to the nearest
millivolt. A gang switch marked "Functions" provides for the
following operations: (1) "SBT" illuminates the taut-suspenslon
type galvanometer. (Optical magnification with two mirrors
-12
throws a hair-line image on the translucent scale*)
At this
stage the mechanical sero of the galvanometer may be ad­
justed by means of a slow motion screw at the right side
of the case.
(2) "STD*" provides for adjustment of the
potentiometer working current by balancing the latter agalnst a standard Weston cell in the usual manner*
adjustment is made by the rheostat marked STD*
This
(3) "GAL."
enables the operator to measure the potential of the mercury
anode with respect to the solution using a normal calomel
electrode*
The last three functions select the three po­
tential ranges, 0 -1, 1 -2, 2 - 3 volts*
The selector
switch marked "Sensitivity" operates a universal shunt,
whereby the galvanometer currents are reduced in known
functions*
panel*
The multiplying factor is indicated on the
Banana-plug conneotors are employed for connecting
the dropping cathode, anode and calomel cell*
The mercury
reservoir and connecting tube of neoprene are supported on
the instrument case as shown*
Details of the electrode as­
sembly are shown in Figure IS* All accessories and con­
nections to the cell are mounted on a rigid bakellte bracket*
The glass cell is brought up from below and secured with a
small swinging shelf with attached locklng-sorew*
The
bracket holds the dropping electrode capillary, connection
to the anode, the calomel cell and a glass tube for flushing
the solution with a gas for the removal of oxygen*
13 -
nitrogen
or hydrogen may he used*
The glass tuhe is provided with
two outlets controlled by a two-way stopcock, one for bub­
bling the gas through the solution and a by-pass for steam­
ing gas over the surface of the solution to prevent re­
entrance of air after deoxygenation of the sample.
The
bakelite bracket is also provided with a rubber gasket on
its under side to engage the lip of the glass cell*
cells are used for the potentiometer*
Dry
The galvanometer is
illuminated with a small lamp operated from a small stepdown transformer*
An independent switch is provided for
the galvanometer*
A switch is also provided to reverse
potentials on the two mercury electrodes, i.e., anode and
cathode*
The rheostat marked "Bias" may be used to supply
opposing potentials, i.e* to reduce any initial galvanometer
deflection to sero*
RESULTS
SYSTEM 1.
Figure 16 shows a complete manually recorded curve ob­
tained with the instrument*
The solution contained the nitrates
of copper, bismuth, lead, cadmium and zinc in a concentration
of 0*0010 normal*As an indifferent electrolyte, tartaric acid
in a concentration of 0*1 normal was employed and adjusted to
pH 5*1 with 0*5 normal ammonium acetate using bromcresol greenmethyl red (0.04£) as a mixed indicator (9) which has a neutral
gray color at this pH value*
The indicator also served as a
maximum suppressant (10 )*
14
System 2.
Figure 17 illustrates the use of the Instrument in quali­
tative polarography.
The solution contained 0.1 normal LiCl
as an indifferent electrolyte and was 0.0010 molar with re­
spect to thallous chloride.
No maximum suppressant was neces­
sary.
As an anode a heavy duty normal calomel cell ( area *
O
21.2 cm) was connected to the solution with a salt bridge
one limb of which contained agar agar made up in half-satu­
rated KC1.
The purpose of the heavy duty calomel cell was to
obtain the half wave potentials referred directly to a defi­
nite potential.
sample.
The curve was taken three times on the same
The half wave potential was estimated in the usual
manner and found to have an average value of -0.497 t 0.001
volts.
The height of the wave which is a measure of the
diffusion current was found to be 47.2 1 0.3 scale divisions.
The three curves are included on a single graph, each one
being displaced along the abscissa for the sake of clarity.
Figures 18 and 19 are the results obtained for the same ion
except that heavy duty saturated and o.l normal calomel cells
were used as anodes.
The solutions in these two Instances
also contained a trace of sodium methyl red which, as can be
seen, made the curves more symmetrical.
-15-
The following table susmarises the results:
*
H
Calomel Cell
Bi/o for T1
potential (volts)
'fvolts)
with hydrogen - 0.000
Ex/g for Tl+
referred to..„
S.C.E.
1.0 normal
+ 0.281 v.
-0.497 v.
- 0.462 volts
Saturated
+ 0.246 v.
-0.462 v.
- 0.462 volts
0.1 normal
+ 0.336 v.
-0.551 v.
- 0.461 volts
*Bl/ 2
- symbol for the "half wave potential"
S.G.E. - saturated calomel electrode
The results Indicate the change in half wave potential
(®i/2) with type of standard cell used.
The values when
referred to the saturated calomel electrode give an average
value of -0.462 t 0.0003 volts.
The value of Kolthoff and
Lingane (4) for approximately the same concentration (i.e.
0.001 molar) is -0.460 volts.
System 3.
Figure 20 shows the negligibly small change In half wave
potential over a four-fold change in concentration, the devi­
ation from the average value of -0.597 was i 0.0003 volts and
illustrates how this constancy of the half wave potential is
one of the most important characteristics of these eunrwntvoltage curves from the standpoint of qualitative polarography.
The solution electrolysed contained 0.1 normal KC1 as in­
different electrolyte and concentrations of Cd(105)2 of 0.00060,
0*0010 and 0*0020 normal with a trace of sodium methyl red*
Each curve was taken only once*
The straight line at the
left shows the proportionality of the current Increment to
the concentration*
The two symmetrical potentials were -0*500
and -0*700 volts* a separation of 200 millivolts*
System 4.
To Illustrate the utility Of the instrument In quanti­
tative polarography using the increment technique the follow­
ing study was made*
Into 50 ml* of deoxygenated 0*1 normal
KC1 solution containing methyl red* successive portions of
a 0*1 normal KC1 solution that had been saturated with oxygen
from a commercial tank at a pressure of one atmosphere were
added from a 10 ml* mloroburette* After each addition the
solution in the electrolysing vessel was mechanically stirred*
The two symmetric potentials were chosen from a complete manu­
ally recorded curve for a 0*1 normal solution of KC1 satu­
rated with air*
Figure 21 is the curve which exhibits two
characteristic waves* the first is the reduction of oxygen
to hydrogen peroxide and the second is the reduction to water
(11)*
The two symmetric potentials chosen were -0*100 and
-0*650 volts respectively*
Figure 21 shows the plot of the
increment for oxygen as a function of the concentration of
oxygen*
The curve in this instance is not a straight line
but curves slightly at the lower concentrations*
agrees with that of Petering and Daniels (3)*
-17
The result
PART III
INTRODUCTION
We have seen that the pioneer work In polarography was
done with the recording pol&rograph of Heyrovsky and Shlkata
and our own researches dealt with the manual method, with
the development of oertain refinements and simplifications*
It ooeurred to us that the use of the cathode ray oscillo­
graph might permit the instantaneous recording of polarograma*
During the course of the work with the oscillograph,
about to be desorlbed, Matheson and Niools (12) of the Dow
Research Laboratories took up the same problem from a point
of view differing somewhat tram, our own*
The method consists of the insertion of a small 60 cycle
a*o* voltage in series with the main d*o* potential which is
being applied to the cell*
The resultant polarographle
currents vary approximately sinusoidally about the mid-point
of the current voltage curve*
These ourrents when amplified
and applied to the vertical deflection plates of a cathode
ray oscillograph will yield a sine wave trace, if and only
if the correct d*e* potential for the given ion has been ap­
plied*
For the d.c* potentials above or below the correct
value, distorted wave patterns will result*
It is therefore
possible to rapidly Identify any reducible ions in the system*
THEORY OF THE METHOD
Let curve QAHBC of Figure 23 represent an Idealised
•18*
eurrent-voltage curve for a certain ion*
The potential, V,
corresponding to point H, if the "half wave” potential for
the ion. Now imagine a small sinusoidal alternating potential
of peak value, AV, applied in series with the main direct po­
tential V*
The current, 1, will now vary about the mean value,
H, to produce a wave, S, of the same wave form and frequency,
but with an amplitude which depends upon the steepness of the
curve ABB*
If the main direct current potential, V, is now
shifted, the sine wave, 3, will become distorted at its upper
or lower portion because of intersection with the non-linear
portions of the curve at B or A*
If this curve, S, is con­
tinuously viewed on the oscillograph screen it will be almost
perfeetly sinusoidal and undlstorted when and only when V has
a value corresponding to the midpoint of the current-voltage
curve (at H)*
Conversely, the appearance of sueh undistorted
waves, as V is varied from zero to the maximum value of depo­
sition potentials, will serve to detect and Identify the
characteristic half wave potentials*
APPARATUS
The circuit used is shown in Figure 24*
It consisted of
the electrode assembly B and two 1*5 volt dry cells B which
supply the direct current potentials through a regulating re­
sistor, radio volume oontrol type Rg, 200 ohms, and a Leeds
and Northrup 100 d m uniform slide wire voltage divider Ri
which was made direct reading in volts*
The small alternating
potential In series with the direct eurrent potential is
supplied by a step-down transformer,
, and a 100 ohm radio
volume control type voltage divider 1*2 * The lead to the
dropping mercury cathode passes through the high gain, low
Impedance (200 ohms) transformer, T2, which was built into
the amplifier A**
The modified alternating current develops
an alternating potential across the secondary of transformer
Tg which after suitable amplification drove the vertical de­
flector plates of a DuMont type 168, nine inch oscillograph*
The horizontal deflector plates were driven by the usual saw­
tooth 60 cycle sweep circuit provided with look-in for the
phenomenon under investigation*
In order to out down pick-up of stray alternating po­
tentials to a minimum all electrloal parts Including the electrode assembly and the lead from the dropping mercury electrode were provided with electrical shielding*
PROCEDURE
Since an undistorted sine wave depends upon a symmetrical
eurrent-voltage curve it was again necessary to eliminate
maxima by including, in all solutions electrolysed, which
with one exception where gelatin was used, was the sodium
salt of methyl red (4) to the extent of about 0,2 ml* of a
0,04% solution*
Nitrogen from a commercial tank was used to
«In the design and building of the amplifier, the helpful ad­
vice of Dr* R.L*Carman, of this department, was greatly ap­
preciated*
20-
deoxygenate all solutions * the tine of flashing being approxi­
mately thirty minutes*
The electrode assembly was the same
as that in the first part of the work*
The small alternating
potentials varied from 20 to 70 millivolts*
In Investigating
a system an alternating potential of approximately 10 milli­
volts from the voltage divider Rg was applied and then the
dlreot current potential from the voltage divider
was in­
creased manually from sero to the half wave potential*
The
dropping rate was adjusted to a somewhat slower value than
that used In the first part of this work* namely* to about
one drop every six seconds*
This was necessary in order to
satisfactorily photograph* all patterns whioh are not
stationary but disappear to give a horisontal straight line
when a mercury droplet fell from the capillary*
As the suo-
eeedlng droplet lnoreases in slse the pattern corresponding
to it begins to lnorease in stature reaching its maximum
height at the instant the droplet falls from the capillary*
The photographs* in all cases* are for the maximum height
of the pattern*
To eliminate measurement of the anode po­
tential wherever possible the solutions were made 0*1 molar
with respect to KC1 and saturated with reagent grade HggClg
thereby forming an internal 0*1 normal calomel electrode
whioh acted both as anode and as standard oell*
The half
wave potentials oould then be referred to the half wave po­
tentials obtained by the usual method by other investigators*
notably Kolthoff and Llngane (4)
* m the photography of these patterns* the suggestions and
helpful advice of Dr* M* B* Dros were greatly appreciated*
-21-
RESULTS
System 1,
The first system studied was a solution containing
cadmium as the nitrate in a concentration of 0V001 normal
with 0.100 normal KC1 to investigate both the reproducibili­
ty of the method and to determine what complications, if any,
arise from the Introduction of the small alternating current
component.
No anode potential existed using a 0.1 normal
calomel cell as one electrode either before or after the de­
terminations whose values are given in the table below.
Applied E.M.F.
(volts)
Average
Deviation from Average
(volts)
-0.688
+ 0.001
0;690
+ 0.003
0i686
- 0.001
0.685
- 0.002
0.686
- 0.001
0.687
0.000
0.688
0.688
+ 0.001
+ 0.001
0.683
- 0.004
0.688
+ 0.001
-0.687 t 0.002 volts
Half wave potential for Cd** referred to saturated calomel
electrode - -0.687 - 0.092 = -0.595 £ 0.002 volts.
The above value of -0.595 compared favorably with that of
Kalthoff and Llngane who give -0.593 at the same concen­
tration.
As can be seen the maximum deviation was 0.004
volts indicating the fairly high reproducibility of the
method.
-22-
System 2.
The second system studied was to show the effeot on the
pattern by keeping the alternating current component constant
while varying the direct current potential.
To 100 ml. of
0.1 normal KC1 was added 1 ml. of a 0.10 normal CddOglg so­
lution.
Referring to the idealized curve of Figure 23, if we
have the d.c. potential set approximately midway between points
0 and A then the current will not vary with time and we should
obtain a straight horizontal line as a pattern.
no. 1 shows the actual pattern obtained.
Photograph
It is not a straight
line but is a modified sine wave form which is due to pick-up
of stray a.c. potential by the amplifier.
This pattern, how­
ever, served as a very satisfactory criterion of the absence
of any reduction prooess occurring at the dropping mercury eleotrode.
It is smaller than the pattern obtained when the
d.c. potential corresponded to point A in the above figure,
which, as one would expect is taller and at the same time is
distorted at its lower portion.
no. 2.
This is shown in photograph
The same is true for the pattern obtained at point B
as photograph no.3 shows, except that now the wave form is
distorted at its upper portion.
Approximately midway between
B and C one obtains the pattern shown in photograph no.4 which
is of the same general character as photograph no.l but smaller
due possibly to the fact that the slope of portion BC is
smaller than that of OA.
Photograph no.5 shows the wave form
obtained at the half wave potential of cadmium.
-23-
The wave form
compares favorably with that of the sine wave form In photo­
graph no.5 which is that obtained by applying a 60 cycle a.e*
to the vertical deflector plates of the oscillograph.
The
half wave potential was determined five times and the results
are indicated below.
Applied B.M.F. (volts)
Deviation from Average (volts)
-0.694
0.698
0.690
0.694
0.694
Average
0.002
0.006
0.002
0.002
0.002
-0.692 i 0.003 volts
Corrected Average
Va
+
+
+
+
-0.683 t 0.003 volts
for Gd++ referred to saturated calomel electrode:
-0.591 1 0.003 volts
The value of -0.591 volts is in satisfactory agreement
with the value of Kolthoff and Lingane of -0.593 volts.
Photograph no. 6 shows the alteration that the pattern at
the
*or cadmium underwent when too great an alternating
potential was used.
This Immediately suggests a way of getting
the correct a.o. component, namely, by first applying a small
a.o. and then at the Bj/ 2 increase it to a point not quite suf­
ficient to give the distortion shown in photograph no.6 . This
procedure was followed throughout all the investigations.
To illustrate the unique characteristic of this method,
namely, that the previous discharge of one ion is not super­
imposed on the discharge of a second when the latter is reducible
-24-
at a more negative potential, 1 ml, of 0*10 normal Zn(N03)2 ,
acidified to prevent hydrolysis, was added to the system used
above.
The values of Kolthoff and Lingane show that the E^yg
of zinc is 0,396 volts more negative than that of cadmium.
Photograph no,7 shows the pattern obtained at E^yg for zinc.
Five readings were taken as indicated below.
Applied B»M,F, (volts)
Deviation from Average (volts)
- 1.096
1,094
1.096
1.096
1.096
Average -1,096
Z
0.000
- 0,002
0,000
0,000
0.000
0,0004 volts
Corrected average
-1,087 ± 0,0004 volts
Bjyg fop Zn++ referred to S.C.B,* -0,995
Z
0,0004 volts
The value of -0,995 agrees fairly well with that of
-0,989 determined by Kolthoff and Lingane,
The separation of
the two potentials as determined by the oscillographic method
came out to be 0,404 volts Instead of 0,396 volts.
Photographs nos, 8 , 9 and 10 show the patterns obtained
when the d.c. potential was at points A, B and midway between
B and C respectively for zinc ion.
As can be seen, they re­
semble very closely the corresponding photographs obtained
for cadmium,
Kolthoff and Lingane give a E^yg for lead in a concen­
tration of 0.001 normal of -0.396, approximately 200 milll-
* Saturated calomel electrode
-25-
volts loss negative than cadmium.
Accordingly, 1 ml, of
0.10 normal Pb(N03)g was added to the solution above which
already contained cadmium and zinc.
Photograph no, 11 shows
the pattern obtained at the E^yg *or load.
The results of
five determinations are given below.
Applied E.M.F,(volts)
Deviation from Average (volts)
0,490
0;484
0,492
0,496
0.492
Average
+ 0.001
+ 0,007
+ 0,001
+ 0,006
+ 0.001
-0,491 i 0,003 volts
Corrected average -0,482 t 0,003 volts
E^yg for Pb44 referred to S,C,E,
-0,390 t 0,003 volts
At approximately midway between E^yg for Pb+4 and
Sjy2 for Cd44 the pattera looked as shown in photograph no, 12,
It shows a complete separation of lead and cadmium.
System 3.
Following the satisfactory separation of lead and cadmium
with the preceding system, the next two systems were studied
in order to establish how dose the two half wave potentials
could be and still give a practical separation on the oscillo­
graph,
The first one studied was lead and cadmium in a
KNaC^H^Og solution (13) that was 0,1 normal with respect to
KC1,
*
Figure 25 shows the manual curve obtained for this system,
5
—
—
"
All manual curves described in this part were taken with the
"BLSCDROPODB" described in Part II,
-26—
The cadmium E^/g
millivolts more negative than the
lead with its bottom portion merging into the top portion of
the lead curve.
It should be noticed that there is no "pla­
teau" separating the ions.
Photograph no, 13 shows the pattern obtained at the £1/2
for lead.
The results are indicated below.
Applied E.M.F. (volts)
Deviation from Average (volts)
- 0,580
- 0,679
0,581
0.583
0.580
-0,001
-0,002
0,000
+0.002
-0.001
Average -0,581 ± 0,001 volts
The average value of -0.581 volts agrees exactly with the
one obtained from the manual curve in the usual manner.
Photograph no, 14 shows the pattern obtained at the E3./2
for cadmium.
The values of the five determinations are listed
below.
Applied E.M.F. (volts)
Deviation from Average (volts)
- 0.732
0.731
0.732
0.730
0.729
+0.001
0.000
+0.001
-0.001
-0.002
Average -0,731 4 0,001 volts
An estimation of the E^yg for Cd44 from the same manually
recorded curve gave -0,737 volts which agrees fairly well with
the oscillographic value.
At a d.c, potential of -0,656, mid­
way between the two half wave potentials, the pattern was as
shown in photograph no, 15 whioh is less than one half the size
of either of those corresponding to the B^yg for Pb44 and Od44.
-27
It is unmistakably distorted and similar to that of a pattern
obtained on a "plateau" as shown In photograph no* 16*
She
latter pattern was given at a d*e* potential of -0*845 volts*
of 114 millivolts above the Xj/g Ta^ua of 0d*
The other system studied* to see whether lead and
thallous ions could be separated on the oscillograph* gave
negative results because In 0*1 normal KC1 their X^yg P°“
tentials are separated by only 61 millivolts*
In a 100 ml*
of 0*1 normal KC1 solution containing thallous Ion In a
concentration of 0*0010 normal the Xj^g was -0*549* as
Indicated In the data below*
Applied X.M.F* (volts)
Deviation from Average (volts)
♦ 0*002
+ 0.002
0*550
0*550
0*547
0*545
0*548
-
0*001
- 0*003
0*000
Average -0*548 t 0*002 volts
The value of -0*548 when referred to the saturated
calomel electrode (no measurable anode potential was ob­
served) gave a value of -0*456 whieh agrees well with that
of Kolthoff and Lingane of -0*457 at the same concentration*
The pattern obtained at the Xj^g potential Is shown in photo­
graph no* 17*
However* In the solution containing both lead and
thallous Ions In 0*001 normal concentrations only one sine
wave form was obtained as shown In photograph no* 18 at a d*e*
-28-
potential of -0*615 volte (average of 5 settings). Indicating
that the two current waves merge into each other firing differ­
entiation impossible* An examination of the couplete manu­
ally recorded curve (Figure 26) for the system reveals that
the manual method is equally incapable of distinguishing be­
tween two ions whose Bj/ 2
The
ere so closely situated*
f°r the combination from the manual curve was -0*528
as compared to -0*515 for the oscillograph*
System 4*
The next system studied was to determine the lowest
concentration of a bivalent metallic ion that could be de­
tected by the oscillographlo method*
Starting with 50 ml*
of 0*1 normal KC1 with cadmium in a concentration of 1 x 10
—5
normal, the concentrations of cadmium ion were increased by
adding 1 ml* portions of a 0*0010 normal cadmium nitrate
solution in 0*1 normal KC1 from a 10 ml* mleroburette* After
the third 1 ml* portion, which made the concentration of Cd++
6*6 x IQ' 5 normal, a pattern shown in photograph no* 19 ap­
peared,
The pattern indicated beyond a doubt that a re­
duction process was taking plaoe at the mercury cathode*
The values of five settings are given below*
Applied B*M.F* (volts)
Deviation from Average (volts)
- 0*690
+ 0*001
0*686
- 0.003
0*689
0.000
0*686
- 0*003
+ 0*003
0*692
Average -0*689 t 0*002 volts
-29
Kolthoff and Lingane do not give a value for cadmium
in this low concentration.
Their average value of -0.599
over a fifty fold change in concentration agrees with the
oscillographic value of -0*597 volts.
The pattern at
while not as symnetrioal is still larger than the one ob­
tained at -0.850 above the Bjy2 Ta^u® afl 18 shown in photo­
graph no. 20.
The pattern obtained below the B^y2 T&lu®
0.550 while almost the same size as the
pattern did
not alter its distorted form upon varying the d.e. potential
as did the Kjyg pattern. Indicating that the size was due
solely to the excessively high amplification necessary to
identify the small modified a.o. component.
The oscillo­
graphic value of -0.689 compared favorably with -0.693 ob­
tained from a manually recorded curve shown in Figure 27.
As has been shown, the individual
potentials can
be determined independently in a mixture containing two or
more ions, when these ions have B^/2 potentials about 160
millivolts apart.
system studied.
This fact formed the basis of the last
To 100 ml. of a 0.1 normal KC1 solution
were added 10 ml. of a 0.20 normal copper sulphate solution
and 1 ml. of a 0.10 normal cadmium nitrate solution.
Gela­
tin to the extent of 0 .2J6 final concentration was used to
eliminate the very great maximum due to copper.
plete manually recorded curve is shown in Figure
The com­
28.
It
was taken at 1/50 sensitivity, beeause copper, present in
large concentration, gave a very large diffusion current.
-30
The concentration of the oopper was 18.0 x 10“® normal and
the concentration of cadmium was 9*0 x lO"4 about onetwentieth that of the copper*
Photograph no* 21 shows the
pattern obtained at a d.c* potential of -0*150 volts.
At
-0.525 volts a pattern (photograph no. 22) characteristic
of the "plateau" was obtained*
At -0*733 volts a pattern
characteristic of a reduction process appeared although
somewhat small because the concentration of copper being
very high, the amplification had to be cut down* However,
now backtracking was resorted to starting at -0.900 (photo­
graph no. 23) with a higher amplification.
At the Bx/2 *>or
cadmium we now have a larger pattern as shown by photo­
graph no. 24.
Backtracking further down to -0*150 caused
such a larger pattern for oopper that it moved off the
screen, giving such & low intensity that it could not be
photographed*
At the same time no damage was suffered by
the oscillograph* An estimation of the Bjyg ^rom the manu­
al curve (Figure 28) gave -0*739 volts while the oscillo­
graphic value was -0*732 volts, an average of the five
readings listed below*
Applied B.M.F. (volts)
Deviation from Average (volts)
- 0*732
0*736
0.730
0.733
0.731
+
+
-
Average -0.732 * 0*002 volts
-31-
0.000
0*004
0.002
0*001
0*001
SUMMARY
1*
Two new methods have been developed for measuring
and interpreting reduotlons at the dropping mercury cathode.
The first, or increment method, is based on a recognition
and proof of the essential symmetry of the current voltage
curves, thus leading to the choice of two symmetrically
disposed potentials and using the resultant current incre­
ment as an accurate measure of the concentration of the electroreducible species.
The extension of this idea to
the use of the ratio of two increments between the unknown
ion and a reference ion of known concentration resulted in
a pilot ion technique which is of very great convenience in
practical analysis.
2.
The instrumental simplifications and Improvements which
resulted from the work permitted the design of a compact
and portable instrument which is now widely used for analy­
sis with the dropping mercury electrode.
The instrument
is primarily suited for the manual recording of the com­
plete curve or for the Increment method or the pilot ion
technique.
3.
Studies with the cathode ray osoillograph have shown
the feasibility of obtaining continuously visible instan­
taneous "polarograms" • This method is primarily suited
for rapid qualitative identification and is characterised
by a wide range of sensitivity and is almost wholly free
from possible damage by overloading.
4«
These various methods while developed primarily for the
practical demands of analytical chemistry yield values for
the identifying potentials and for their quantitative esti­
mation somewhat superior in precision to the prevailing
values which are to be found in the literature*
-33-
BIBLIOGRAPHY
(1) Heyroraky* J*:
Phil* Mag* 45, 309 (1923)
(2)
Heyrovaky, J* and Shikata, M* t Rae* frav, tide* 44,
496 (1925)
(3)
Petering, H.G* and Daniela, F* : J* A. C* 3* 60, 2796
"” (1930)
(4) Kolthoff, I.M* and Lingane, J,J* t Chem* Rots*, 24,1
(33fc9)
(6)
HeyroTaky, J*; In V* B&ttger "Physlkallaehe Methoden
dar Chenlsohen Analyse", yo I* 2,
pp* 260-322, Akadanisohe ‘tferlagsgesellaeh&ft n*b*H*, Lelpalg, 1936*
(6) Hohn, H* : "Chenlsohe Analyaan nit den Polarographen",
Jhllna Springer, Berlin (1937)
(7)
Vitek, V* t Coll* Cseoh* Chen* Com* 7, 537 (1935)
(8)
Heyrovaky, J* and UkoYie, D* tColl* Cseoh* Chen* Conn*
7, 198 (1935)
(9)
Kolthoff, I*M* and Sandall, E*B*i Textbook of Quanti­
tative Inorganic Analyala, pp 429 (1937)
(10) Raynan, B* t Coll* Cseoh* Chen*Coom* 3, 314 (1951)
(11) Raaoh, J* t Coll* Cseoh* Chen*Conn* 1, 560 (1929)
(12) Matheaon, L*A* and Nlchola, H* t Trans* Bleotrochen* Soo*
75, 193 (1938)
(13) Suohy, K«i Coll* Cseoh* Chen* Coast* 5, 354 (1931)
54-
R
■m-
n
LEGEND FOR FIGURE 1
A - Leeds and Northrup, 4 dial precision resistance box
( 9999 ohms )
B - 3 ohm radio-type potentiometer
C - Double-pull, double-throw switch
D - Standard Weston Cell
E - Leeds and Northrup student-type potentiometer
S - Switch
P - 0*1 megohm protecting resistance
F - Electrode assembly
G - Wall galvanometer, Leeds and Northrup Type P
103 megohm sensitivity, internal resistance « 126 ohms
period 8*9 seconds, C.D.R*X* * 30,000 ohms
H - Galvanometer shunt of two Leeds and Northrup
4 dial precision boxes ( each 9999 ohms )
I - Saturated calomel reference electrode
/
LEGEND POE FIGURE 2
A - Pool of mercury earring as anode
B - Rubber bulb
C - Platinum wire inseal to anode
D - Hydrogen gas inlet
E - Hydrogen gas outlet
P - Mercury reservoir
G - Platinum wire inseal to cathode
H - 10 ml., capacity micro-burette
M - Manometer and scale
PB- Presstire bottle
R - Micro bubble regulator
S - Two-way stopcock
20
F ig . 3
1.11
deflection
16
Zn
12
0.68
•
Cd
-0.4
'
T
-0.8
1.2
•
APPLIED E.M.F. <VOW’S)
1.6
Data for Figure 3
Applied E.M.F.
(volts)
Net Galvanometer Deflection
in cma._________
-0.130
0.0
0.200
0.4
0.300
0.400
0,500
0.600
0.650
0.675
0.700
0.750
0.800
0.900
1.000
1.050
1.075
1.100
1.126
1.150
1.176
1.200
1.300
1.400
1.500
0.8
0.9
1.0
1.1
2.5
6.0
10.1
12.5
12.6
12.7
13.0
13.5
14.5
16.5
19.2
21.5
22.6
22.9
22.9
22.8
22.7
Galvanometer sensitivity 3 maximum
*The dropping mercury electrode was the cathode
throughout this work.
24
20
P ig . 4
MET OALV. DEFLECTION
16
12
8
4
0
0
1.2
APPLIED S.U.F. (VOLTS)
Data for Figure 4
Net Galvanometer Deflections.in ems. at
__________ Molea of OdClo « 10*________
Applied E.M.F.
(volts)
-0.200
0.500
0.400
0.500
0.600
0.650
0.675
0.700
0.750
0.800
0.900
1.000
1.100
Curve
0.40 0.75
1.1
1.5
1.9
2.3
2.7
3.0
0.6
1.1
0.4
0.9
0.3
0.1
0.1
0.1
0.2
0.6
1.3
1.4
1.5
1.0
1.2
1.2
0.3
0.7
0.9
0.7
0.3
0*5
0.3
0.4
0.5
0.3
0.4
0.4
0.5
1.6
1.4
1.9
1.9
2.4
2.8
2.9
3.1
3.2
H
1.0
1.1
1.2
2.0
0.8
0.6
0.9
0.7
1.1
2.0
1.0
3.5
3.6
3.8
4.0
4.2
3.4
4.3
4.5
4.6
4.8
5.0
3.8
5.1
5.2
5.4
5.5
5.7
0
F
B
2.8
0.6
0.6
1.1
2.8
0.6
6.4
6.4
6.5
2.5
5.2
7.0
7.3
7.5
7.6
7.7
8.7
0.7
1.3
3.3
6.7
9.2
9.5
9.6
9.7
9.8
D
C
B
A
2.3
4.5
6.0
6.2
0.6
1.1
5.9
8.1
8.4
8.5
8.6
8
Pig. 6
INCREMENT
6
4
2
0
0
0.8
1.6
2.4
Cone. Cd, Moles X 104
3.2
Data for Figure 5
Concentration of Cd,
Moles x 104
Increment in Galvanometer
Deflection in caa.
0.40
1.4
0.75
2.4
1.1
3.4
1.5
4.3
1.9
5.5
2.3
6.7
2.7
7.8
3.0
8.8
40
Fig. 6
52
OMLVm INC
24
16
0
4
8
Cone. Cd, Moles X 104
12
Data for Figure 6
Concentration of Cd,
Moles x 104____
Galvanometer Increment In ems.
at -0.600 and -0.800 volts
1.3
4.6
2.4
8.4
3.6
12.0
4.8
15.7
6.0
19.2
7.1
22.6
8.1
25.6
9.1
28.9
10.0
32.0
11.1
35.2
12.1
38.2
APPLIED B.M.F. (VOLTS)
Data for Figure 7
Applied E.M.F.
(volts)
-0*033
0.100
0.200
0.300
0.400
0*500
0.600
0.626
0.650
0.675
0.700
0.750
0.800
0.850
0.900
1.000
1.100
1.200
Net Galvanometer Deflection
in ei
0.0
10.2
12.0
12.7
13.0
13.4
14.4
17.1
23;9
33.6
41.4
46.8
47.8
47.9
48.0
48.0
47.9
47.7
32
fi«.e
GALV. INCREMENT
24
16
8
0
16
Cone. Pb, Mol©a X lo4
V . .•./
Data for Figure 8
Concentration of Pb,
Moles x 10*____
Galvanometer Increment in one*
at -0«400 and -0«90C volts
3*9
7.4
7*3
14.2
10*6
20*6
13.8
26*4
16.6
31.4
Cone. Zn, Holes X 10
Data for Figure 9
Concentration..of Zn,
Moles x 10*_____
a&lT&noneter Increment in one*
at -1.000 and "*1,500 volts
0.64
2.4
3*23
6.2
5.44
9.3
7.32
12.1
8.87
14.4
11.4
17.8
13.5
21.0
15.1
23.2
16.4
25.0
•H
N
tO
rl
CO
Data for Figure 10
Concentration of Cd,
Moles x 10*_____
Galvanometer Increment in eaa.
at -0.600 and -0.800 volts
1.6
1.2
2.6
1.8
3.8
2.9
5.6
4,0
7.5
5.1
9.4
6.3
11.6
7.6
13.9
9.1
16.5
10.5
19.2
12.4
22.4
14.8
26.1
16.6
29.5
S2
24
16
8
0
4
8
Cone* Pb, Moles X 10^
12
Data for Figure 11
Concentration of Pb,
Molee x 10*_____
Galvanometer Increment in one*
at -0.400 and -0.900 volte
3.8
7.4
7.4
14.0
10.7
20.2
13.8
25.9
16.6
30.6
APPLIED E.K.F. (VOLTS)
rl
to
Honoa'idaa ‘Amro
00
o
Data for Figure 12
Applied B.M.F*
(volte)
-0*000
0*050
0*100
0*150
0*200
0*220
0*240
o;26o
0*280
0*300
0*550
0*450
0*550
0*650
0.700
o;7so
0*800
0*820
0;840
0*860
0;880
0*900
0*940
0*980
1*000
1*050
1*100
1*150
1*200
i;250
1*300
1*320
1*350
1*380
1*400
1*420
1*450
1*500
1*540
1*560
1*580
1*600
1*650
1.700
1*750
1*800
1*860
Net Galvanometer Deflection
In cma*
-1.4
—1*2
-1*0
-0.3
1*6
4*2
6*7
8*0
8*4
8*5
8*6
8*7
8*8
8*8
8*8
8*9
9*5
10*5
12*1
13.6
14*6
15*1
15*7
16*0
16*1
16*3
16*3
16*4
16*5
16*6
17.3
17.9
19*1
20*3
21*1
21.7
22*3
22*9
25*2
23*3
23*3
23*4
23*4
23*4
23*5
23*6
23*9
FIG. 13
"PILOT"
ION
COPPER - ZINC
C
UNKNOWN
TO
ZINC - COPPER
CADMIUM-ZINC
RATIO,
B
A
DEFLECTION
CADMIUM - COPPER
0
2
4
6
CONCENTRATION
8
10
MOLAR x
12
I0 4
14
Data for Figure 13
982
982
33.2
7.4
6.3
982
10.8
10.1
5.7
3.7
982
34.1
14.9
14.0
10.
6.2
34.6
18.9
18.0
10.
34.5
22.5
10.
10.
10.
34.1
10.
0.10
0*08
0.22
0.19
0.32
0*30
0.44
0.41
0.65
0*62
0.65
0*68
0.76
0.72
0.98
0.98
2.4
2.4
5.2
8.5
6.5
7;e
7.6
35.1
26.5
25.2
10.
35.1
30.6
29.2
10.
10.2
10.2
0.87
0.83
35.1
35.2
33.1
10.
11.8
11.8
1.00
0.94
35.1
40.7
39.1
10.
1.16
1.12
gss
?83
20.1
Ratio of
ZiV^Cu
for
Curve C
&8§? PS8
982
32.8
3.3
2.7
982
Copper as "pilot" ion
Ratio of
Ret Galvanometer
Cono. of Ions,
Cd/Cu
Deflection in oas. Moles z 104
for
_____________ _ _______________ Curve A
8.9
8.9
13.7
13.7
Data, for Figure 13
Zine aa "pilot" ion
820
10.
28*6
7.3
6.7
10.
28.6
11.4
10.
10.0
Ratio of
Cd/Zn
for
Carre B
Ratio of
Cu/Zn
for
Carre D
.07
•06
1.4
1.4
.
0.26
0.23
0.40
0.35
0.55
0.47
0.71
0.61
0.86
0.72
0.96
0.80
2.7
2.7
4.1
4.1
28.6
15.7
13.4
10.
28.3
10.
820
17.2
880
28.4
24.0
20.4
10.
880
28.0
26.8
22.4
10.
800
28.4
29.2
24.4
10.
10.2
10.2
1.03
0.86
SS0
5.6
5.6
28.0
31.6
26.4
10.
11.1
11.1
1.13
0.94
S00
820
820
29*2
3.7
3.6
820
let Oalranometer
Cone* of lona,
Deflection in eaus. Moles x 10*
28.4
34.8
29.2
10.
12.1
12.1
1.23
1.03
20*0
7.1
7.1
8.4
8.4
9.2
9.2
CALOMEL
F is h e r S c ie n t if ic C o
P i t t s b u r g h ,p a .u .S. A.
VOLTS
N 0U 03U 3Q
U313W0NVA1V9
Data for Figure 16
Applied B.M.F. (volte)
-0.160
Seale Reading (div.)
- 0.8
0.200
0 .0
0.225
0.260
0.275
-*■1.5
6.5
18.1
15.0
15.7
15.8
16.3
18.3
24.5
27.9
29.6
30.0
30.2
33.0
40.0
44.8
46.2
46.4
47.1
50.1
57.0
60.1
61.0
61.2
61.2
61.2
61.1
61.0
61.0
62.0
65.0
0.600
0.325
0.350
0.375
0.400
0.425
0.460
0.600
0.550
0.600
0.650
0.675
0.700
0.725
0.760
0.800
0.825
0.850
0.875
0.900
0.950
1.000
1.050
1.100
1.150
1.200
1.260
1.275
1.300
1.325
1.350
1.375
1.400
1.450
68.6
71.7
73.6
74.6
75.1
76.1
Sensitivity of Galvanometer z
2.75 x 10“® amps./div.
H
Nonoa'idaa *aivo
APPLIED
E.M.F.
(VOLT;
Data for Figure 17
Curre A
Curve B
Applied
Seale
l.M.F.
(volte) Reading
-0*000
o;ioo
0,200
0*300
0*400
0*440
0*470
0*500
0*530
0*560
0*600
0*660
0.700
0*800
0*900
1.000
-6*8
3,2
0*9
+0.7
3*3
8*0
16*0
28.0
39*1
46*0
49*2
50*1
so;s
51*2
52*0
52*2
Applied
Scale
E.M.F*
(volte) Reading
-0.000
0*100
0*200
0*300
0*550
0*400
0*430
0*460
0*500
0*530
0*560
0*600
0*650
0.700
0*800
0*900
1.000
Half wave
Potential
-0*496 volts
-7.0
4*5
1.0
+0*7
1.7
3*8
6*2
12*0
28*2
39*4
46*7
49*5
50.3
50*8
51*9
52*8
52*8
-0*496 volts
Curve C
Applied
B.M.F.
(volts)
-0*000
0*100
0*200
0*300
0*350
0*400
0*430
0*460
0*500
0*530
0*560
0*600
0*650
0.700
0*800
0*900
1*000
Scale
Reading
-6*9
3*3
0*9
+0*9
2*0
4*0
6*9
12*0
28*1
40*0
46;9
50*1
51*1
51*2
52*0
53*3
53*6
-0*498 volts
Average
Half wave
Potential s -0*497 t 0*001 volts referred to 1*0 N Calomel Cell
Sensitivity of Galvanometer s one-fifth
Heavy duty 1*0 H Calomel Cell as anode
'1
\
CO
(VOLTS)
?
E.M.F.
?
APPLIED
tO
CM
?
o
c
*
$
s
Moiioa’id a a • atto
Data for Figure 18
Curve A
Curve B
Applied
Seale
B.M.F.
(volts) Reading
0.000
0.100
0.200
-0.8
0.3
0.275
0;350
0.380
0.420
0;450
0.500
0;530
0.660
0.600
0.650
0.700
0.800
0.900
+0.2
0.1
1.0
2.5
8.9
18.2
36.5
41.8
44.0
45.0
45.2
45.2
45.2
45.2
Curve C
Applied
Seale
E.M.F.
(volts) Reading
0.000
0.100
o;20o
0.275
0.330
0.370
0.410
0.450
0.470
0.500
0.530
0.670
0.610
0.660
0.700
0.800
0.900
-0.9
0.4
0.1
+0.2
0.7
1.8
6.6
18.2
25.8
36.3
41.9
44.3
45.0
45.2
45.2
45.2
45.2
Applied
Seale
E.M.F.
(volts) Reading
0.000
0.100
0.200
-0.9
0.4
0.275
0.320
0.360
0.390
0.420
0.450
0.480
0.620
0.560
0.600
0.650
0.700
0.800
0.900
+0 .2
0.1
0.6
1.3
3.6
8.8
19.0
30.4
40.6
44.0
44.9
45.1
45.1
45.1
45.1
Half
Potential = -0.462 volts
Average
Half wave s
Potential
-0.463 volts
-0.461 volts
-0.462 ± 0.001 volts referred to Saturated Calomel Cell
Sensitivity of Galvanometer s one-fifth
co
<0
APPLIED
E.M.F.
?
(VOLTS)
?
N
q
K o iio a r m a *a it o
q
Data for Figure 19
Curve A
Applied
E.M.F.
Seale
(volte) Reading
0.000
0.100
o;2oo
0*300
o;s50
0*400
0.440
0;460
0.510
0;540
0.570
0*500
0*630
0;670
0.710
0;760
0.800
0.660
1.000
Half wave
Potential
-2*5
0*8
0*3
0.1
+0*1
0*6
1*3
4.2
io;i
20.7
32*0
42*1
46.6
48*8
49*3
49.3
49*4
49*3
49*3
-0*551 volte
Curve B
Curve C
Applied
Applied
Seale
JLxaite) Reading
(volts)
E.M.F.
0*000
0*100
0.200
0*300
0*350
0*400
0*460
0*500
o;s30
0*560
0*600
0;630
0*650
0;680
0.710
0*750
0*800
0*900
1*000
-2*4
0*9
0*3
0.1
+0*1
0*6
2*1
7.7
15;9
28*3
42*0
46*7
48*1
49*1
49*3
49*3
49*4
49.3
49*3
-0*551 volts
E.M.F.
0*000
0*100
0*200
0*300
0*350
0*400
0*430
0*470
0*500
0*530
0*560
0*590
0;620
0*650
0.680
0*710
0*750
0.800
0.900
1*000
Seale
Reading
-2.4
o;8
0*3
0.1
+0.1
0.5
0*9
3.2
7.7
is;9
28*3
39.3
45*3
48.1
49.2
49;s
49.5
49;3
49.3
49*3
-0*552 volte
Average Half wave Potential z -0*551 t 0*003 volts referred to
0*1 M Calomel Cell
Sensitivity of Galvanometer Z one-fifth
o
o
to
o
<0
N
GALVANOMETER DEFLECTION
O
o
o
o
o
eg
co
o
<•
<0
eg
o
eg
8*0-
0
eg
1
90-
in
8*0-
MOLAR
CONC. Cd
O
eg
O
V0
m
!N3W 3dO NI
lN 3 d d D 0
( 3 O S) S 1 1 0 A
x 10
VO-
in
eg
Data for Figure 20
Cone*
Curve A
of Cd++ H Z m B O Normal
Applied
B.M.F.
Seals
(volts) Reading
Curve B
"77.TOlTJ"Normal
Applied
E.M.F.
Seale
(volts)
Reading
0.700
0.720
0.740
0.760
0.780
0.800
+1.0
2.0
2.6
3.0
3.2
3.3
3.6
3.7
3.8
4.0
4.2
4.4
5.1
6.2
7.8
11.7
18.6
23.3
29.1
34.7
41.2
46.4
52.3
56.5
58.6
62.5
63.8
66.7
67.6
68.4
68.8
69.0
69.1
69.2
69.2
69.3
69.4
69.5
Applied
E.M.F.
il.
One-half
Sensitivity • One
-0.560
0.400
0.430
0.450
0.460
0.470
0;480
0.490
0.500
o;sio
0.520
o;53o
0.540
0.550
0.560
0;570
0.580
0;585
0.590
0.595
0.600
0.605
0.610
0.615
0.620
0.625
0.630
0.640
0.650
0.660
0.670
0.680
Curve C
*TO025 Normal
-0.350
0.400
0.460
0.480
0.490
0.500
0.510
0.520
0.530
0.540
0.550
0.560
0.570
0.580
0.585
0.590
0.595
0.600
0.605
0.610
0.620
0.630
0.640
0.650
0.660
0.670
0.680
0.700
0.730
0.770
0.800
+0.2
0.6
1.2
1.8
1.8
1.9
2.1
2.3
s;e
3.1
4.2
5.8
9.7
16.7
21.0
26.8
32.2
38.5
43.4
49.4
55.8
61.2
64.6
65.8
66.3
66.7
66.9
67.0
67.1
67.5
68.0
Seale
Reading
One-fifth
-0.300
0.400
0.450
0.480
0.500
0.510
0.520
0.530
0.540
0;550
0.560
0.570
o;s8o
0.585
0.590
0.695
0.600
0.605
0.610
0.620
0.630
0.640
0.650
0.660
0.680
0.700
0.740
0.780
0.830
+0.2
0.5
0.7
0.8
0.9
1.0
1.2
1.4
1.8
2.8
4.1
7.3
12;8
16.4
20.5
24.7
29.6
33.6
37.8
43.0
47.7
60.5
57.4
52.3
52.8
53.0
53.2
53.3
53.7
APPLIED
<M
HI
E.M.F,
(VOLTS)
(O
•
rH
I
CO
?
O
tO
Noiioariaa •a i v o
0
H
1
Data for Figure 21
Applied E.M.F*
(volte)
-0*0
0*050
0*100
0*200
0*260
0*500
0*400
0*500
0*600
0*700
0*800
0*900
1*000
1*100
i;eoo
1*300
1*400
1*500
1.600
Galvanometer Deflection
_____
-1.3
-0.7
40*9
16*3
20.3
21*5
22.7
23*5
24*0
25*3
27.0
30*7
35*9
40*8
41*5
42*2
42*5
42*3
41*8
60
FIG. 2 2
CURRENT
INCREMENT
50
40
30
20
10
2.0
3.0
MICROGRAMS OXYGEN PER CC.
4.0
Data for Figure 22
Applied E.M.F*
(volte)
-0*100
-0*650
Net Galvanometer
ml. of
Mlorograme of'
Deflection
solution added Oxygen per ml*
6*9
0.00
0*00
-0*650
11*6
1*62
0.42
-OilOO
-0*650
15*5
2*92
0*74
22*6
5*40
1*34
28*5
7*39
1*80
35*5
9*83
2*34
43*3
12*56
2*92
52*3
15*98
3*62
62*2
19*42
4*26
- 0.100
- 0*100
-0*650
- 0*100
-0*650
- 0*100
-0*650
- 0*100
-0*650
- 0.100
-0*650
- 0.100
-0*650
Fig. 23
B
H
o
E
\r
o
70
•
Pig. 25
GALV. DEFLECTION
50
■0.737
Cd
30
10
10
- 0 .2
-0.4
-
0.6
APPLIED E.M.F. (VOLTS)
•
•
Fife. 26
-0.528
40
GALV.
DEFLECTION
60
r
20
y
0
-0 .2
—0.4
-0.6
APPLIED E.M.F. (VOLTS)
20
F ig . 27
GALV.
DEFLECTION
- 0.603
40
30
20
0
-0.2
-0.4
APPLIED E.M.F. (VOLTS)
-0.6
NO. 14
No# X15
N o » 2 4-
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