US2728721A - Polarographic electrode assembly - Google Patents

Description

R. K. LADlscH ErAL 2,728,721

POLAROGRAPHIC ELECTRODE ASSEMBLY Filed May 29, 1953 Dec. 27, 1955 I" :'l ll x INVENTORS Rolf Karl LadScL Jl Sanley L.Kz@$back ATTORNEY PoLARoGRAPmC ELEcTRoDE ASSEMBLY Rolf Karl Ladisch, Lansdowne, and Stanley L. Knesbach, Philadelphia, Pa., assgnors to the United States of America as represented by the Secretary of the Army Application May 29, 1953, serial No. 358,578 4 Claims. (Cl. 204-195) (Granted under Title 35, U. S. Code (1952), sec. 266) The invention described herein if patented, may be manufactured and used by or for the Government for governmental purposes without the payment to us of any royalty thereon.

This invention relates to polarographic electrode assemblies of the dropping mercury type.

One of the objects of the present invention is to construct a dropping mercury electrode in such a way that the rate of flow of the mercury and the drop size are maintained very nearly constant. Another object is to simplify the construction. A further object is to construct the electrode so that a single filling of the mercury reservoir will serve for about two weeks in polarographic testing. Another object is to make it possible for the user to see what is happening inside the assembly. A specific object is to control drop times and the m2/3 t1/6 values with a precision of r0.5 per cent.

Other objects will be apparent from the following description of the preferred embodiment of the invention shown in the accompanying drawings forming a part of this specilication.

In said drawings- Fig. l is a perspective view of the assembly;

Fig. 2 is a longitudinal section through the assembly; and

Fig. 3 is a cross section on line 3 3 of Fig. 2.

Referring particularly to the drawings, a tubular body 5, preferably of glass, has a reduced lower end 6 in which a valve cock l is located. A capillary 8 is connected to end 6 by means of Tygon tubing 9. The mercury drops (not shown) or" course fall from the lower end of capillary 8 into the test solution. At its upper end, tubular body 5 merges with a reservoir 10 preferably cylindrical in form. Near its top, reservoir 10 has a filling hole or inlet 11 for introduction of the mercury 12. Coaxial with the cylindrical reservoir 10 is a barometric inner reservoir 13 having a port 14 in its bottom wall 15. The inner reservoir 13 is also preferably cylindrical, and it may have a diameter of about one-half the diameter of the outer reservoir 10. ln the drawings, the ratio of these diameters is about 4:7, which is satisfactory. Preferably inner reservoir 13 is of glass and it is fused at its upper end to the top wall 16 of the outer reservoir 10 so as to depend therefrom and provide an annular chamber 17 of substantial volume between the inner and outer reservoirs. The bottom wall of reservoir 13 lies above the bottom wall of reservoir 10 so that the mercury may flow freely from chamber 1'! through port 14 into reservoir 13 and in the reverse direction. The upper wall 16 is constricted as at 18 to form a truste-conical neck, and a tube 19 is joined to the upper, smaller end of neck 18. A rubber or other collapsible bulb 2i? is fitted on the upper end of tube 19. Near the top of inner reservoir 13 a capillary side arm 21 is attached, with its upper end communicating with the interior of reservoir 13 and its lower end drawn to a point or tip 22. A capillary passageway 23 extends the entire length of the side arm 21, and as shown, the lower pointed end 22 is located well above the bottom wall 15 of the inner reservoir 13. A wire or lead 24 is brought through the glass wall of reservoir 10 and through the wall of inner 2,728,721 Patented Dec. 27, 1955 ICC reservoir 13 and is bent down to make a good electrical contact with the mercury 12 in the inner reservoir. It will be understood that wire 24 is connected to a galvanometer (not shown) and the galvanometer is connected to a source of electric current such as a battery (not shown), while the battery is connected to a polarographic half cell, as in the usualpolarographic set-up. See Fig. 5 of the R. K. Ladisch pending application Serial No. 220,325, Vfiled April 10, 1951, now Patent No. 2,708,657,

issued May 17, 1955, for an illustration of the complete circuit.

To operate the described electrode, valve cock 7 is closed and mercury of the purity demanded forl polarographic use is introduced .through inlet 11 to a height corresponding approximately to half the length of. Athe capillary sidearm 21. Then the rubber bulb 20 is squeezed and released. This forces part of the air (which-was above the surface of the mercury confined in inner reservoir 13 out through the capillary sidearm; this airv escapes in bubbles to the surface of the mercury and enters annular chamber 17, which is open to the'atmosphere. Asthe air in the upper part of inner reservoir 13 is consequently of reduced pressure, the mercury level will rise in inner reservoir 13 to reach a state of equilibrium or a balancing of the pressures. The level in the outer reservoir comes into balance at a height h, which is the height of the lower tip 22 of the capillary sidearm; lthis tip acts as` a valve, permitting air to ow from the outer reservoir into the inner reservoir through the capillary sidearm until the rise in the mercury level in the outer reservoir seals off the tip. The described electrode may then be put in service by merely opening the valve cock 7, whereupon drops of mercury at a known rate will proceed to fall one by one into the test solution. Then readings are taken on the galvanometer in accordance with the well-known polarographic technique. During the course of this analysis, mercury is steadily lost to the electrode by the drops falling from capillary 8, but the level of the mercury in the outer reservoir is maintained at height h until, after many analyses, the mercury in the inner reservoir 13 has fallen close to the level of tip 22. Then the mercury supply may be replenished by introducing additional mercury through inlet 11, and analyses by and polarographic technique may proceed.

The constancy of the mercury level in the described assembly was checked during a series of test runs using a cathetometer. In no case did the deviation exceed 0.5 mm., according to our observation. The drop time t as well as the mass flow m as determined in a one-tenth normal KCl solution, held by a thermostat to 25 C: 0.05", remained constant within 20.5 percent. Some typical data, selected at random from one days operation of the described electrode assembly, are reproduced in the following table:

Table I.-Drop time and mass flow of mercury obtained from 3 capillaries in combination with new electrode assembly.

[Pio N KCI solution, 25;l;0.05 C. Room temperature not controlled] From these data the radii of the capillaries were calculated (Koltho and Lingane, Polarography, vol. I,

p. 80, Interscience Pub., New York, 1952). They were The values calculated by this formula for the capillaries 1, 2 and 3 of the table were 3.24, 5.18 and 6.26 seconds respectively, which is in good agreement with the drop times actually measured.

` The electrode assembly described above and illustrated in the drawings is simple, convenient to manipulate, and extremely reliable. With a given capillary it maintains a constant pressure due to head h overa period of several weeks oncontinuous operation with routine analyses.

What we claim is:

1. A dropping mercury electrode assembly comprising an outer lreservoir open to the atmosphere and having suicient volume to hold a substantial supply of mercury, an inner reservoir wholly enclosed by and spaced from the outer reservoir, said inner reservoir having a bottom wall with a port providing a passage for free How of mercury between the reservoirs, a suction member, the inner reservoir being sealed off from the atmosphere and having means connecting itwith the suction member, a capillary sidearm connected to the upper part of the inner reservoir and extending down in the space between theV inner and outer reservoirs, a valved tube connected to the bottom of the outer reservoir, a capillary, and means connecting the capillary and valved tube so that mercury ows through the valved tube to the capillary and is discharged in drops from the lower end of the capillary.

2. The invention defined in claim l, wherein the suction member is a collapsible rubber bulb, and the outer reservoir is entirely sealed off from the atmosphere except for a lling opening near its upper end.

3. A dropping mercury electrode assembly comprising an outer glass reservoir having a lling port for mercury and having a tubular extension extending downwardly from its lower end, a valve cock in said tubular extension for controlling llow of mercury, a capillary coupled to the lower end of the tubular extension to discharge the mercury in a series of drops for polarographic analysis, an innerglass reservoir fused at its upper end to the upper end of the outer reservoir and receiving its sole support fromits connection with the outer reservoir, there being a substantial space between the walls of the inner and outer reservoirs except at the aforesaid fused joint, the bottom walll of the inner reservoir having a passage for free flow of mercury, a capillary sidearm connected at its upper end to the interior of the inner reservoir and extending down alongside the outer wall of the inner reservoir with its lower end reduced to a ne tip which is spaced well below the medial horizontal plane of the inner reservoir, and a suction means connected with the upper part of the inner reservoir.

4. The invention defined in claim 3, wherein the suction member is a collapsible rubber bulb, and the outer reservoir has an open port near its upper end for introduction and replenishment of the mercury supply.

"Analytical Chemistry, vol. 22, No. 9 (September 1950), pages 1213 and 1214.

Claims (1)

1. A DROPPING MERCURY ELECTRODE ASSEMBLY COMPRISING AN OUTER RESERVOIR OPEN TO THE ATMOSPHERE AND HAVING SUFFICIENT VOLUME TO HOLD A SUBSTANTIAL SUPPLY OF MERCURY. AN INNER RESERVOIR WHOLLY ENCLOSED BY AND SPACED FROM THE OUTER RESERVOIR, SAID INNER RESERVOIR HAVING A BOTTOM WALL WITH A PORT PROVIDING A PASSAGE FOR FREE FLOW OF MERCURY BETWEEN THE RESERVOIRS, A SUCTION MEMBER, THE INNER RESERVOIR BEING SEALED OFF FROM THE ATMOSPHERE AND HAVING MEANS CONNECTING IT WITH THE SUCTION MEMBER, A CAPILLARY SIDEARM CONNECTED TO THE UPPER PART OF THE INNER RESERVOIR AND EXTENDING DOWN IN THE SPACE BETWEEN THE INNER AND OUTER RESERVOIRS, A VALVED TUBE CONNECTED TO THE BOTTOM OF THE OUTER RESERVOIR, A CAPILLARY, AND MEANS CONNECTING THE CAPILLARY AND VALVED TUBE SO THAT MERCURY

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