US2706712A - Portable polarographic half cell - Google Patents

Description

April 19, 1955 R K. LADISCH' 2,706,712

PORTABLE POLAROGRAPHIC HALF CELL Filed March 30, 1954 2 Sheets-Sheet 1 Fig.2.

[LEAR FRITTED GLASS wm+ HgCl-KIII PASTE CLEAR GLASS F 5. INVENTOR BY Wyw ATTORNEY N IiiHil n 'mlll Ill ilil April 19, 1955 R. K. LADISCH 2,706,712

PORTABLE POLAROGRAPHIC HALF CELL Filed March so, 1954 2 Sheets-Sheet 2 I I'I I LQ lllillllli' CL EAR GLASS H mill llnu "in iilll mmm A I PURE MERCURY Hal-.1 K0 PASTE CLEAR GLASS-K I -O.60O ids. vs.5 .CL.E., VOLTS INVENTOR Karl Ladisck ATTORNEY N 2 millimolar- Cadmium waves in O.ln KCl solu-l'ion wH-h +he cells o'F Fl'cbs. 20nd '7.

rates 1 2,706,712 PORTABLE POLAROGRAPHIC HALF CELL Rolf Karl Ladisch, Lansdowne, Pro, assignor to the United States of America as represented by the Secretary of the Army Application March 3t 1954, Serial No. 419,941 Claims. (Cl. zen-195 (Granted under Title 35, U. S. Code (1952), sec. 266) I. J. Lingane and H. A. Laitinen in Ind. Eng. Chem,

Anal. Ed., Vol. 11, p. 504 (1939) and G. S. Smith in The Analyst, Vol. 75, p. 215 (1950), cannot be moved about freely because shaking them sometimes causes inaccuracies of l--3 millivolts or even more, and full accuracy may not be restored until five or six hours have elapsed. Besides, these prior art structures must be kept in an upright position to main the original cleanliness of the platinum contact.

This invention aims to provide a non-polarizable, rugged half cell of low ohmic resistance, especially made .to confine the mercury in a rigid support, so that the electrical contact between the platinum wire and the mercury is not disturbed under the conditions of polarographic procedure. A specific object is to confine the mercury by material which is porous to the mercury when the latter is subjected to pressure. The preferred porous material is glass frit; when choosing a frit of the proper size the area of the mercury can be made equal to or several times larger than that of the mercury pool in a conventional half cell.

The present application is a companion to my pending applications Serial Nos. 372,411 and 373,928 filed respectively August 4, 1953 and August 12, 1953, each of which shows a portable half cell of different construction.

In the accompanying drawings forming a part of this specification,

Fig. 1 is a full size elevation of one form of the half cell, showing a conventional lead for the contact wire;

1 lgig. 2 is an enlarged longitudinal section, omitting the Figs. 3, 4 and 5 are respectively cross sections on lines 33, 44 and 55 of Fig. 2;

Fig. 6 is a reproduction of a curve made from actual tests with the half cell;

Fig. 7 is a longitudinal section through another form of the half cell; and

Fig. 8 is a diagrammatic sectional view partly in elevation showing a set-up, including the half cell of Fig. 7, for analyzing a solution by polarographic methods.

Referring particularly to the drawings, Fig. 1 shows the completed half cell 10 with a lead 11 coupled thereto. The half cell 10 comprises a generally tubular glass body 12 (Figs. 2-5) having a clear glass closed upper end 13, a fritted glass cylindrical body portion 14, and a clear glass lower end portion 15 which is open. In making the fritted glass body portion 12, fritted glass parts with nominal maximum pore sizes of 40 microns and 5 microns were used at random. A glass tube 16 of about half the diameter of the tubular end 15 is fused inside said tubular end 15 so that tube 16 is coaxial with the tubular end 15 but terminates short of the lower extremity of said tubular end. Calomel-potassium chloride paste is deposited within the porous fritted glass wall 14 by means of suction with a water injection pump, in a manner similar to ordinary filtration practice. After this depositing, the interior of the tubular cell is cleaned by washing with distilled water. Then air is sucked through the fritted glass until the latter becomes dry. Then the interior of the cell is filled with pure mercury 17 bypouring the mercury in through the open end of the body 12,

2,706,712 Patented Apr. 19, 1955 ICC.

which is of course inverted for this step. Some of the mercury stands in tube 16 as shown. Then the contact wire 18 (platinum or tungsten) is inserted in the mercury, after having been electrically and mechanically connected to the end of lead 11 by means of soft solder 19. Finally, the lower end of the half cell is sealed by means of a mass of cement 20 which is placed inside the open tubular end 15 and inside the lower end of tube 16. Cement 20 should have good dielectric characteristics and when it sets or hardens it provides a rigid support or anchorage for the contact wire 18. The bottom of the glass tube is closed by a rubber or similar stopper 21 having a central opening 22 through which lead 11 passes, and having a circular flange 23 which surrounds the tubu lar end 15. When the parts are assembled, some of the cement 2!), while still plastic, will flow through opening 22 and into the space between flange 23 and the outer wall of tubular end 15; and when the cement hardens the rubber stopper will be secured tightly to the tubular end 15,- also lead 11 will be firmly secured to the rubber stopper and hence to the half cell assembly.

The modification shown in Figs. 7 and 8 comprises a half cell essentially the same as the one shown in Figs. l'-5 except that it has no open end through which the mercury may be poured, hence it is more difiicult to make. The half cell 30 has a generally tubular glass body including a clear glass closed upper end 31, a fritted glass cylindrical body portion 32, a tubular clear glass lower end portion 33, which is open, and a fused wall 34 closing and sealing the lower end but terminating short of the lower extremity of the glass body. In making the fritted glass body portion 32, fritted glass parts with nominal maximum pore sizes of microns and 5 microns were used at random.

To complete the half cell, the part delivered by the glass blower was placed in a desiccator and was evacuated by means of a high vacuum pump for at least an hour. Still under vacuum, triple distilled mercury was admitted through a funnel in the lid of the desiccator in such a fashion that the mercury filled the space around the wall of fritted glass. The mercury penetrated through the wall (when made of coarse glass frits) as soon as the desiccator was returned to atmospheric pressure, to fill the entire interior of the half cell, as indicated at 35. (If the frits were of 5 microns pore size, a pressure of 75 p. s. i. gage from a nitrogen cylinder was applied to the mercury to accomplish the same result. This latter operation was done in a stainless steel bomb, to which the glass half cell body, including the mercury,.had been transferred from the desiccator.) After filling the half cell, any excess mercury clinging to the outside walls was shaken 011. A paste made of KCl solution (special for calomel cells, into which 0.35 per cent by weight of agar had been dissolved) plus calomel (special for calomel cells) was brushed onto the outer surface of the fritted glass body portion 32. Electrical contact with the mercury is made by fusing a tungsten wire 36 through aperture 37in Wall '34, which is-accomplished before filling the half cell with mercury. A piece of soft solder 38 mechanically and electrically connects wire 36 to lead 11, and a mass of insulating cement, 39 (like cement 20) closes the lower end portion 33 and anchors the lead to the assembly. Finally, a flanged rubber stopper 40 (like stopper 21) is fitted on the lower end of the half cell body, being secured by cement 39 as Fig. 7 indicates.

Referring to Fig. 8, the half cell of Fig. 7 has its principal portion immersed in a sealed container 41 containing KCl solution 42, with a surrounding water jacket 43 (having connections 44 and 45 with a thermostated water bath) to keep the temperature of the half cell substantially constant. Also located in the sealed container 41 above the half cell is an open vessel 46 closed at the lower end by a very thin resinous membrane 47 whose under surface is in direct poptact with the KCl solution 42. My pending application Ser. No. 220,325 filed April 10, 1951. discloses vessel 46 in more detail. The open vessel 46 contains the solution to be tested by the apparatus (not shown) and a dropping mercury electrode 48' drops mercury 49 into the test solution in the well known manner. A battery 50 with a rheostat 51, 'a 'galvanometer 52, and a lead 53 to the dropping mercury electrode, are also shown. Thecircuit is completed by lead 11 which is connected to the rheostat 51. As the technique of using the described polarographic apparatus is well understood, no description thereof will be undertaken.

The half cell of Figs. 7 and 8, like the half cell of Figs. l5, even when handled frequently during an analysis, will perform satisfactorily. Both cells are obviously rugged and compact and are easily handled and packaged. With the conventional mercury pool electrode, great care had to be exercised to arrive at equally precise results, but in routine polarographic analysis, precise results cannot be expected from the conventional electrode.

The potential of the half cells described herein was checked in saturated KCl solution against a saturated calomel electrode, in combination with a potentiometer and a galvanometer. The a 'erage deviation of all cells tested was 0.3 rnillivolt; these small deviations decreased even further after the cells came to equilibrium over night.

Polarograplric analyses of 2.00 millimolar cadmium sulfate in 0.1 normal KC]. solution were conducted in a Lingane-Laitinen H-cell. The test compartment was sepparated from the reference electrode by an agar plug as usual. For comparison, a conventional mercury poolcalomel reference electrode in saturated KCl solution was placed in the bottom of the H-cell adjacent to the test compartment, the half cells herein described being likewise immersed in the saturated KCl solution above the mercury pool electrode. The surface area of the mercury pool was 3.8 sq. cm. In view of the fact that the poterilial of the pool electrode may become inaccurate under certain conditions, this electrode was prepared with extreme care, and once it had been set up in the thermostated H-cell, it was neither removed nor mechanically disturbed. The pool electrode was renewed whenever significant changes in its potential (as measured. against a calomel electrode) became apparent despite the precautions taken. Removal of the test solution and clearing of its compartment were done with a suction tube. The test solution was free from oxygen by purified nitrogen prior to the analysis, and nitrogen was passed over the solution during the analysis as is usual. The drop time of the capillary used was checked during each run at the half wave potential; it maintained a value of 4.89:0.01 sec. The m t value was found to be 1.83 at an applied potential of 0.70() v. versus SCE, at which the magnitudes of the diffusion currents were determined. The capillary cell equipment was kept at 25:O.1 C. by means of a thermostat control. A well known commercial manual polarograph was employed. polarographic circuit Was measured. All data were corrected for the IR drop and the residual current.

To detect possible time-dependent changes in potential of the cells herein described, five curves were drawn consecutively with readings based on the same test solution. Approximately 45 minutes elapsed between the first and the last measurements. The heights of the diffusion currents at an applied voltage of O. 60,0 v. versus SCE (i. e., close to the half wave potential) agreed with each other to better than :05 per cent.

Fig. 6 shows the 2 millimolar cadmium sulfate curves obtained with the conventional mercury pool-calomel reference electrode and the two half cells described herein. The values measured for the curvesoften coincided.

The diffusion currents measured at an applied potential of -700 mv. with the hereindescribed half cells were within the ranges of 13.05:0.05 microamperes for the 2 millimolar solution. The half wave potentials were read from individual curves for each reference cell at /2 id (where 'id is the average diffusion current in microamperes during the life of the drop of mercury). The readings agreed with each other within 597:0.5 millivolts. The comparative resistances in ohms were as follows:

Conventional Half Cell Half Cell 'iost Solution g Pool Electrode Call Fig. 2 Cell Fig. 1

2 millimolni l, 160 1,120 1,140

The IR drop across the 1.83. The electrolysis was not diffusion controlled, since no maximum suppressor was present. The value found in this manner for Ia was 3.58, which is in very good agreement with the data of Buckley and Taylor (Res. Natl. Bur. Stand. Vol. 34, p. 97, 1945) who obtained 3.54 for cadmium ion in the absence of a maximum suppressor. The half Wave potential of 59710.5 mv. agrees well with Linganes value of 5991-2 mv. (I. Am. Chem. Soc, Vol. 61, p. 2099, 1939).

Although the portable calomel half cells of this invention have been described with particular reference to their use in polarographic analyses, because of the great importance of having a reference electrode in such analyses which is very stable, it is to be understood that the portable hair" cells of my invention may be used wherever calomel reference electrodes are needed.

What I claim is:

l. A portable polarographic half cell comprising a unitary generally tubular body having an upper wall providing a closed upper end, a lower end, and a chamber on the inside which is completely filled with mercury, the side walls of the tubular body being principally of porous fritted glass, and a calomel-potassium chloride paste all of which is on or in said porous fritted glass walls; a conductor entering the l wer end of the tubular body and making electrical contact with the mercury in the cha rnber; and means to secure the conductor immovably upon the half cell.

'2. A portable polarographic half cell comprising a unitary tubular body having a closed upper end of clear glass, a main body portion of porous fritted glass, calomelpotass-ium chloride paste all of which coats or impregnates the fritted glass, and a lower end of clear glass; the interiorv of the body providing a chamber, and mercury completely filling said chamber; a conductor extending through said lower end into the chamber and making electrical contact with the mercury therein; and sealing means closing said lower end and securing said conductor against movement within the chamber.

3. The invention defined in claim 2, wherein the sealing means includes a mass of cement principally contained within the lower end of the body and surrounding said conductor, said sealing means also including a rubber stopper fitting over the lower end of the tubular body and confining the cement, said rubber stopper having a central aperture through which the conductor extends, part of the cement forming a layer or film between the rubber stopper and the lower extremity of the tubular body and another portion of the cement surrounding the conductor at the area where it passes through said central aperture.

4. A portable polarographic half cell comprising a generally tubular body having a closed upper end made of clear glass, a porous fritted glass portion extending for the principal length of the body, a clear glass lower end portion which is open, and an internal tubular portion fused to the walls of the lower end portion and extending coaxially therewith, said tubular portion having a diameter materially less than the diameter of the lower end portion and terminating short of the extremity of said lower end portion, the interior of the body being hollow, mercury completely filling said interior, a paste of calomel and potassium chloride all of which coats or impregnates the porous fritted glass portion, a conductor in contact with the mercury and extending out through said lower end portion, and means sealing the lower end portion and securing said conductor.

5. A portable polarographic half cell comprising a generally tubular completely closed body having a closed upper end made of clear glass, a porous fritted glass portion extending for the principal length of the body. a clear glass lower end portion which is closed, the interior of said body being hollow, mercury completely filling said interior, a paste of calomel and potassium chloride all of which coats or impregnates the porous fritted glass portion, a conductor in contact with the mercury and extending out through said closed lower end portion, and giec'ims securing said conductor to the lower end of said References Cited in the file of this patent UNITED STATES PATENTS 2,672,441 White Mar. 16, i954 FQREIGN PATENTS 733.;630 Germany Mar. 31, 19,43

Claims (1)

1. A PORTABLE POLAROGRAPHIC HALF CELL COMPRISING A UNITARY GENERALLY TUBULAR BODY HAVING AN UPPER WALL PROVIDING A CLOSED UPPER END, A LOWER END, AND A CHAMBER ON THE INSIDE WHICH IS COMPLETELY FILLED WITH MERCURY, THE SIDE WALLS OF THE TUBULAR BODY BEING PRINCIPALLY OF POROUS FRITTED GLASS, AND A CALOMEL-POTASSIUM CHLORIDE PASTE ALL OF WHICH IS ON OR IN SAID POROUS FRITTED GLASS WALLS; A CONDUCTOR ENTERING THE LOWER END OF THE TUBULAR BODY AND MAKING ELECTRICAL CONTACT WITH THE MERCURY IN THE CHAMBER; AND MEANS TO SECURE THE CONDUCTOR IMMOVABLY UPON THE HALF CELL.

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