US2768135A - Electrolytic cell - Google Patents

Description

Oct. 23, 1956 S. L. ADELSON ELECTROLYTIC CELL.

Filed Aug. 4, 1955 IN V EN TOR.

United States Patent C) ELECTROLYTIC CELL Application August 4, 1953, Serial No. 372,308

6 Claims. (Cl. 204 359 This invention relates to electrolytic cells for measuring electrieally-determinable characteristics of liquids, such as conductivity, 0. R. P. (oxidation-reduction potential),

pH (hydrogen ion concentration) various ion concentrations, or D. 0. (dissolved oxygen). More particularly, the invention is concerned with an improved through-flow cell of the type wherein the liquid whose electrically-determinable characteristic is to be measured is a part of a closed pressure system.

It is an object of this invention to provide an improved electrolytic cell of the type including a noble metal electrode in direct contact with the liquid sample whose characteristic is to be measured, and a reference electrode, such as, for example, a calomel electrode, which is in ionic contact with the liquid sample through a salt bridge.

Another object is to provide in an electrolytic cell of this general type means to keep the noble metal electrode and the interface between the salt bridge and the flowing liquid sample free of deposits.

Another object is to provide an improved electrolytic cell of this general type which is suitable for measuring an electrically-determinable characteristic of a flowing liquid under pressure and necessitates a minimum of cleanmg.

Another object is to provide a through-flow electrolytic cell including means for keeping a clean interface between the flowing liquid sample and the salt bridge and preventing pollution of the salt bridge by the liquid sample.

Another object is to provide an electrolytic cell of this general type wherein means are provided to cause a slight, controlled flow or oozing of the electrolyte forming the salt bridge across the salt bridge-sample interface.

Other objects will become apparent upon consideration of the description and of the claims which follow.

It is well known to measure characteristics of a liquid, such as conductivity, 0. R. P., pH, or D. 0., by means of electrolytic cells and to utilize the potential dilference or current developed by the cell for indicating and for controlling the value of the characteristic measured. For example, the potential or current can be applied to a controller which actuates a feeder or a valve to provide the quantity of treating agent needed in order to maintain the desired value of the characteristic.

It has long been recognized that, in order to obtain accurate readings, the electrodes of an electrolytic cell must be kept free of deposits of foreign matter and of films of slime or the like. Many expediencies have been proposed to avoid the necessity of frequent electrode cleaning, such as projecting abrasive material against the electrode surfaces. When dealing with liquid containing relatively large quantities of suspended and dissolved organic matter, it is not only important to keep the electrodes clean, but it becomes also imperative to prevent deposits in all portions of the cell. Obviously, the decomposition of organic matter deposited in any part of the cell will alter the composition of the liquid sample and prevent accurate measurements. To keep the electrodes, as well 2,768,135 Patented Oct. 23, 1956 as the cell body, free of deposits, it has been suggested to provide through-flow cells and to establish a flow through the cell of sufficient velocity to continuously sweep the contact areas of the electrodes and prevent settling in the through-flow passage. In the operation of such through-flow cells it has been found that the usual gelatinous or fiber plug or wick, or other porous closure, constituting the interface between the liquid sample and the salt bridge, is subject to the deposition of organic films which interfere with exact readings and thus necessitate frequent cleaning of the cell.

Such filming can be prevented by causing a small, controlled flow, in the form of individual drops or oozing of the electrolyte forming the salt bridge through the porous closure separating the salt bridge from the liquid sample. Alternatively, the porous closure may be replaced by an open-ended capillary tube to establish direct contact of the electrolyte with the liquid sample, and a controlled flow can be induced therefrom.

To obtain a flow through the porous closure or from the capillary tube, I provide means in the through-flow conduit for reducing the pressure in the vicinity of the closure or capillary tube to a value below that of the head of the electrolyte on the closure or capillary tube. The reduced pressure at the point of liquid junction between the salt bridge and the liquid in the through-flow conduit serves the double purpose of causing the flow of electrolyte which keeps the junction clean, and of preventing the liquid sample from entering the porous closure or capillary tube and polluting the salt bridge.

The means for reducing the pressure may take a variety of forms and be based on various flow principles or combinations of such principles. Thus, the flow area of the liquid sample may be reduced with resultant increase in velocity, or the flow may be turned around a corner. Various shaped bodies can be introduced in the flow stream with a pressure reduction occurring downstream thereof. A pressure decrease can also be obtained in a pump suction line or a siphon. Some means based on these principles are shown in the drawings while others will become apparent to those skilled in the art upon consideration of the detailed description and the drawings, wherein similar elements are designated by the same numerals.

Figure 1 is a diagrammatic vertical cross-sectional view of a cell according to the invention;

Figure 2 is a diagrammatic partial vertical cross-sectional view of another embodiment of the invention;

Figure 3 is a diagrammatic plan view of another embodiment of the invention; and

Figure 4 is a diagrammatic partial vertical cross-sectional view of still another embodiment of the invention.

In the figures the liquid whose characteristic is to be determined flows through a conduit 10 in the direction of the arrows. The conduit 10 is made of non-conducting material, such as glass, or plastic material. The liquid entering conduit 10 may be the entire flow through a treating plant; ordinarily, however, a sample flow will be by-passed from the main flow through the inlet end of conduit 10 and may be returned to the main flow at any suitable part of the plant, or in some cases be sent to waste, through the outlet end of conduit 10.

An electrode 15, preferably of a noble metal, such as platinum or gold, has a surface in a section of conduit 10 of suitable length. As shown in Figures 1 to 3, the electrode 15 extends only partway around the inner surface of the conduit 10; however, if a larger surface area is desired, it may be extended around the entire inner surface, as shown in Figure 4. The electrode 15 is shown for clarity as a plate, but it can be a thin metal foil, or a metal film deposited on the inner surface of the conduit it) in known manner. A wire 16 extends from the outside through the wall of the conduit and is connected to the electrode 15. When the cell is in use, the wire 16 is connected in an electrical circuit with wire 17 which is connected to a reference electrode 20 of suitable material, such as calomel.

As shown in Figure l, the reference electrode 20 extends through a plug 111 into a reservoir 22 which may be filled with potassium chloride or other electrolyte forming a salt bridge between the electrode 2%) and the liquid flowing through the conduit 10. The reservoir 22 may be of sufficient size to hold a large supply of electrolyte, or, as shown in Figure l, a supply tank 23 may be connected to the reservoir 22 by a valved pipe 24.

The salt bridge and the sample liquid communicate by means of a capillary connection 25, which may be a porous closure 25:: with numerous minute openings, as shown in Figure 2, or, as shown in the other figures, a single capillary tube 251) open to the reservoir 22 and to the conduit it). In either case, the connection 25 will be located in a zone of reduced pressure so that a small flow of electrolyte through the capillary connection is induced, which will keep the interface between the electrolyte and the liquid sample clean of films and deposits. Further, the liquid sample, which may be under a higher pressure than the head of electrolyte over the capillary, is prevented from entering the capillary and polluting the salt bridge by the reduced pressure at the point of capillary connection. The small amount of electrolyte which is continuously exuded from the reservoir 22 through the capillary connection 25 can be replenished from the supply tank 23, to maintain a substantially constant liquid level in reservoir 22.

In Figure 1 the means for obtaining a reduced pressure are shown in the form of a venturi tube 30 inserted in the conduit 16*. The noble electrode preferably is installed upstream of the throat 31 of the venturi while the capillary connection 25 shown in the form of a tube 25b opens to the venturi throat 31. The reduction in fluid pressure due to the reduced flow area at the venturi throat 31 induces a slight flow of liquid from the capillary tube 25b into the conduit 10. In this manner the liquid forming the junction between the salt bridge and the liquid sample is continuously renewed, and film formation and deposits are prevented.

In Figure 2 the liquid junction between the salt bridge and the flowing liquid sample is located on the suction side of a pump 35 installed on, or otherwise connected with, the conduit 19a. The conduit 10a may be of any desired configuration. The inlet end of conduit 18a is submerged below the liquid level L of the tank or pit from which the liquid is pumped, and extends preferably to a higher elevation than the level L to prevent a pressure buildup in conduit 10a in case the pump 35 accidentally fails to work.

In this embodiment the liquid in the reservoir 22 communicates with, and is exuded through, a porous plug or closure 25a, which may be a gelatinous or fiber plug or the like; but it will be understood that a capillary tube, as shown in the other figures, could be used instead. As the pump 35 is operated, a small amount of electrolyte is oozed through the porous plug 25a into conduit 10a, whereby the surface of the plug is continuously washed and freed of deposits and films.

In Figure 3 the means for obtaining a reduced pressure comprises an elbow-shaped portion 49 in the conduit 10. The reservoir 22 is connected to the elbow 40 by a capillary tube 25b, as shown. The electrode 15 may be arranged just upstream of the junction of the capillary tube 25b with the elbow 4d. The pressure reduction due to the liquid changing its direction of flow exudes a small flow from the capillary tube, so that the liquid junction etween the salt bridge and the flowing sample is continuously reformed by fresh electrolytic liquid.

Figure 4 shows still another means for obtaining a pressure reduction in the vicinity of the point of ionic communication between the liquid sample and the electrolyte forming the salt bridge. In this figure the capillary tube 25b and the surrounding tube in which the capillary is sealed are extended into the conduit 10 in the direction of flow, whereby a reverse Pitot tube 45' is formed. The resultant pressure reduction in conduit 10 downstream of the tube 45 will suck a small quantity of electrolyte from the capillary tube 25b and keep the interface between the salt bridge and the flowing liquid sample clean.

While the above means for obtaining a pressure reduction have been shown and described for purposes of illustration in separate embodiments, several of these means can be combined with advantage in a single installation. Thus, for example, when the pump 35 of Figure 2 is used, an additional reduction in pressure can be obtained by a slight restriction of the conduit 10a in the vicinity of the porous closure 25a. The same is true of the embodiment of Figure 4, where a slight restriction of the conduit 10 around the reversed Pitot tube 45 will provide an additional slight pressure reduction. Similarly, while the conduit of Figure 4 has been shown for purposes of exemplification as a straight tube, it could be in the form of an elbow, as shown in Figure 3. Other combinations will be obvious to those skilled in the art. The choice of the particular means, or combination of means, for obtaining a pressure reduction depends on the value of the reduction needed and other features of individual installations. Thus, where the liquid sample flow must be pumped, utilization of the pump suction, as in Figure 2, for obtaining the pressure reduction will be in order, while in a gravity flow system the venturi of Figure 1 might be preferable.

While the noble metal electrode 15 has been shown in Figures 1 and 3 for purposes of illustration upstream of the capillary connection between the electrolyte forming the salt bridge and the liquid sample, it may be located in the conduit just opposite the capillary connection, as shown in Figures 2 and 4 as the velocity in this vicinity is sufiicient to immediately divert the small flow of electrolyte in downstream direction. Further, the noble metal electrode 15 need not form a part of the inner surface of the conduit 10, as shown in the drawings, but can take any suitable shape as it is continuously washed by the liquid flowing through the conduit 14). This is particularly true if the electrode 15 is installed in the area of reduced pressure and high velocity flow.

It will be obvious to those skilled in the art that the electrolytic cell shown and described herein will be enclosed in a suitable casing, not shown, so that it may be installed as a unit.

Various modifications can be made without departing from the scope and spirit of the invention. Thus, the conduit 10 could be a siphon and the capillary connection be located at its top. It will, therefore, be understood that I do not wish to limit myself to the exact structural features shown in the drawings for purposes of exemplification but not of limitation.

Iclaim:

1. An electrolytic cell for measuring an electricallydeterminable characteristic of a flowing liquid comprising a conduit for flow of the liquid whose characteristic is to be determined, a first electrode having a contact area in communication with the liquid flowing through said conduit, .a second electrode, a body of electrolyte in communication with said second electrode and also in ionic communication with the liquid flowing through said conduit, and means connecting said electrodes in an electrical circuit, characterized by means for continuously keeping said first electrode and the point of ionic communication between said body of electrolyte and the liquid flowing through said conduit free of deposits, said means comprising a device effective to lower the pressure in a portion of said conduit below the head of said body of electrolyte on said point of ionic communication, said first electrode and said point of ionic communication being located in the said portion of said conduit wherein the pressure is lowered.

2. The apparatus of claim 1 wherein said device effectivetglgwer the pressure is a venturi tube forming at least part of said conduit, said first electrode is located within said venturi tube upstream of its throat and said point of ionic communication of said body of elecrtolyte with the liquid flowing through said conduit is at the throat of said venturi tube.

3. The apparatus of claim 1 wherein said device eifective to lower the pressure comprises a pump installed on said conduit With its suction side downstream of said first electrode and of said point of ionic communication.

4. The apparatus of claim 1 wherein said device effec tive to lower the pressure is an elbow section in said conduit, said first electrode is installed in said elbow section, and said body of electrolyte is in ionic communication with the liquid flowing through said elbow.

5. The apparatus of claim 1 wherein said ionic communication comprises a capillary tube extended into said 20 conduit in the direction of flow, and said first electrode is located in said conduit in the zone of reduced pressure created by said capillary tube.

6. In an electrolytic cell for determining an electricallydeterminable characteristic of a flowing liquid, said cell being of the through-flow type and including a liquid flow conduit, a first electrode having a contact area adapted to be in communication with liquid flowing through said conduit, a second electrode, a salt bridge in contact with said second electrode and in ionic communication with liquid flowing through said conduit, and means connecting said electrodes in an electrical circuit, a venturi tube forming at least part of said conduit, said ionic communication comprising a capillary connection with the throat of said venturi tube, said venturi tube being shaped to cause a sutficient reduction in pressure at said throat to induce a flow from said salt bridge through said capillary connection, said first electrode being mounted in the zone of reduced pressure in said venturi tube.

References Cited in the file of this patent UNITED STATES PATENTS 667,559 Neubauer Feb. 5, 1901 1,513,558 Parker Oct. 28, 1924 1,951,205 Rather et a1 Mar. 13, 1934 2,219,616 Bradshaw et a1. Oct. 29, 1940 2,289,687 Stuart -a July 14, 1942 2,382,735 Marks Aug. 14, 1945

Claims (1)

1. AN ELECTROLYTIC CELL FOR MEASURING AN ELECTRICALLYDETERMINABLE CHARACTERISTIC OF A FLOWING LIQUID COMPRISING A CONDUIT FOR FLOW OF THE LIQUID WHOSE CHARACTERISTIC IS TO BE DETERMINED, A FIEST ELECTRODE HAVING A CONTACT AREA IN COMMUNICATION WITH THE LIQUID FLOWING THROUGH SAID CONDUIT, A SECOND ELECTRODE, A BODY OF ELECTROLYTE IN COMMUNICATION WITH SAID SECOND ELECTRODE AND ALSO IN IONIC COMMUNICATION WITH THE LIQUID FLOWING THROUGH SAID CONDUIT, AND MEANS CONNECTING SAID ELECTODES IN AN ELECTRICAL CIRCUIT, CHARACTERIZED BY MEANS FOR CONTINUOUSLY KEEPING SAID FIRST ELECTRODE AND THE POINT OF IONIC COMMUNICATION BETWEEN SAID BODY OF ELECTROLYTE AND THE LIQUID FLOWING THROUGH SAID CONDUIT FREE OF DEPOSITS, SAID MEANS COMPRISING A DEVICCE EFFECTIVE TO LOWER THE PRESSURE IN A PORTION OF SAID CONDUIT BELOW THE HEAD OF SAID BODY OF ELECTROLYTE ON SAID POINT OF IONIC COMMUNICATION, SAID FIRST ELECTRODE AND SAID POINT OF IONIC COMMUNICATION BEING LOCATED IN THE SAID PORTION OF SAID CONDUIT WHEREIN THE PRESSURE IS LOWERED.

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