US1990768A - Electrode apparatus - Google Patents

Description

Feb. 12, 1935. w. J. YOUDEN 1,990,758

ELECTRODE APPARATUS Filed Sept. 5, 1935 5 Sheets-Sheet 1 Feb. 12, 1935. w. J, YoupEN 1,990,768

ELECTRODE APPARATUS Filed Sept. 5, 1933 3 Sheets-Sheet 2 Patented Feb. 12, 1935 1,990,768

UNITED STATES PATENT OFFICE v ELECTRODE APPARATUS William J. Youden, Yonkers, N. Y., assignor to W. M. Welch Manufacturing Company, Chicago, Ill., a corporation of Illinois Application September 5, 1933, Serial No. 688,148

7 Claims. (Cl. 2045) The present invention has to do with a device vestigators to the present time have been of bulb used for determining the hydrogen ion concenshape, or have been bulbs with depressions t tration of solutions and relates particularly to hold the sample. All of these bulbs required athe electrode used therewith. considerable portion of the sample. Another For the purpose of understanding the origin type of electrode consisting of a hollow tube with 5 and development of thepresent device, a brief a thin glass membrane across its end is capable statement of the early history of glass electrodes of using as little as two drops of such sample. and their use is given. Each of the electrodes used required more skill In the development of means for determining in its preparation than the electrode to be dehydrogen ion concentration, the advent of the scribed herein. 10

quinhydrone electrode greatly facilitated the For the purpose of explaining the nature of a measurement of hydrogen ion concentration in glass electrode, a specific application will be used.

many solutions. It eliminated the bulky source When proper aqueous solutions are separated of hydrogen gas. It also eliminated the diiliby a thin glass wall, there exists a difierence in culties with solutions which foamed excessively, potential between the two solutions; this dif- 15 and the troublesome preparation of electrodes ference, as a rule, bears a Simple relationship which frequently become poisoned and useless. to the difierence in density of free hydrogen ions Especially gratifying was the diminished time (hereafter designated by the symbol pH) of the required for equilibrium. The quinhydrone solutions.

electrode was not a, perfect electrode by any If the pH of either of thesolutions iS known, 20

means, and it had its special utility in acid soluthe pH of t other y be obtai ed by us tions. In practice, it did not give accurate data already compiled from the use of the glas values in solutions more alkaline than pH 8.5. ectrode.

Repeatedly the question has arisen as to the Notwithstanding that .the glass electrode, like 5 possible interaction of the quinhydrone with the h hydrogen a d th quinhyd n electrode. is material in solution. an electrometric method, the apparatus usually The glass electrode is now on trial. The diflip y for measuring eleetl'omotive forces culty encountered in the glass electrode has been is not u ab The im d te d fi ou y nin the preparation of the electrodes themselves countered With the glass electrode, Which p and in the extreme fragility of the electrodes. rates the q is that the glass OfieIS Such a 30 In the device hereinafter described, these dish resistance to h pas a f rent hat advantages are fairly well eliminat d, I addieven a sensitive galvanometeris not equal to the tion, the quahtity of the material required for ta k of indicating the ineq y of the pp examination has been reduced below one one- Potentialshundredth of a cubic centimeter. Where a quadrant electrometer is employed 35 Up to the present time, in th use of th glass in place of a galvanometer, it is found that a. reelectrode, it would appear that more time has n d c que i nece y. One form of elecbeen used in developing a satisfactory voltagetrometer, however, has been found useful for this measuring device thaninproducingasatisfactory P p That is the Lindemahn electrometer,

40 form of glass electrode. which is rugged, very compact, and requires no 40 At least-four methods of measuring the voltage levelling. Its v n y m is s small that the have been advocated. Early workers used the entire instrument may be Placed on the Stage usual types of quadrant electrometers. Then of a microscope Where the movement f t e came the methods which employ a thermionic indicator needle yb Observed (along a m valve.- These were very bulky. The construccr e scale) h h an ey piec 45 tion of tube equipment in the laboratory a With the introduction into the system of an also difiicult. electrometer that is sufficiently sensitive to be ac- One investigator used and advocat d th baltuated by the minute currents passing through listic galvanometer. Other of the investigators the walls of the glas Capillary, the p s 01 depended upon other types of galvanom ter satisfactory shielding and insulating the system 50 Efiorts have been made to reducethe resistance have become of paramount importance. Evidentof the electrode system to the point that th crly if the set-up requires a potentiometer circuit dinary galvanometer could be used but without in which no deflection of the electrometer is the great success. indication of perfect balance, the slightest static Most of the electrodes employed by the ineffects must be eliminated. The metal box, which 5 is described later and in which allof the parts of the apparatus are housed, furnishes the shielding required. The switches, which form the control parts of the electrometer circuit and provide means for grounding and charging. the quadrants and the needle of the electrometer, must bebuilt with proper insulation of quartz and of bakelite or other similar dielectric substance so as to avoid the slightest leakage of the charges on these parts of the electrometer while observations arebeing taken. The glass-electrode set-up that includes the glass electrode, the connecting vessels and the accompanying calomel .or other half cells, and because it is electrically connected to the needle of the electrometer, must be well insulated by quartz or the like so that, when desired, the charge on the needle may be maintained at a constant magnitude fora period of time.

With this brief statement concerning the field and the prior art'in the scope of the present invention the plausibility of the various objects will be recognized.

It is one object of the present invention to provide a new and improved device or system for the determination of the hydrogen ion concentration of solutions and to make a more rugged and compact device for this purpose than has heretofore been practicable.

Another object of the invention is to provide a new and improved apparatus for the detection of minute difi'erences in electric potentials of solutions whereby the hydrogen ion concentration of one of those solutions may readily be determined.

Another object of the invention is to provide a special three-circuit switch having an especially high insulation factor by the use of quartz and bakelite' or other phenol preparation so that the plates of the Lindemann electrometer may be charged by a 3" battery or grounded at will and the needle of the electrometer charged by the glass electrode cell and also grounded at will.

A still further object of the invention is to provide a unique and improved device in which minute electrical phenomena may be observed and measured free from the influence of outside electrical forces or the like.

These objects, and such other objects as may hereinafter appear are obtained by the novel construction, unique arrangement, and improved combination of elements described in the accompanying specification and illustrated in the attached drawings, hereby made a part of this specification, and in which:

Figure 1 is a vertical section through a complete device embodying the subject matter of the present invention, the arrangement being generally as the apparatus is used;

Figure 2 is a schematic representation of the electric circuits used in the device illustrated in Figure 1;

Figure 3 is a schematic representation of the circuit employed in the electrometer shown in' Figures 1 and 2;

Figure 4 is a view in perspective illustrating a typical glass electrode such as is used in the present apparatus, and the method of cleansing such electrode;

Figure 5 is an enlarged sectional view of the glass electrode shown in Figure 4; and

Figures 6, -7 and 8 are respectively, top, side and end views of the high insulation switch employed in the present apparatus.

Like reference characters are used to designate or it may be entirely of metal.

similar parts in the drawings and in the description of the invention which follows.

For housing the apparat a box 10 is provided. Such a box may be of w interlined with metal In the present instance, the box or cabinet shown in Figure 1 comprises walls of wood with a metal outer casing 11, a metal inner lining 12, and-a metal bottom 13, the metal forming a shi d from foreign electric fields. I;

For convenience in the asse bly of the apparatus and for purposes of inspection, ,the box is provided with a removable cover or top 14. The cover or top is also of wood with metal inner and outer plates and 16 respectively. The electric circuits to be later described are arranged on the sides of the box, being placed on panels which are attached to either side of the box. Stems 1'7 for potentiometer knob 18 extend to the exterior of the box on one side. One such stem and knob are shown in Figure 1; the view of the others is obstructed by those shown. Push buttons 19 and 20 extend through a side of the box at a position above the knobs 18. Suitable openings in the walls of the box and through which the stems and buttons project, permit free manipulation thereof. An opening 21 in the top of the box is provided for the eye-piece 22 of the microscope 23.

'A window 24 is placed in the side of the box for illuminating the needle and scale of an electrometer 25 by permitting the reflection of light in a mirror 26 of the microscope. A millivoltmeter 27 forming a part of the circuit used in the device may be disposed on the under side of the removable top. Reading of the millivoltmeter is had through a window 28. Access to the interior of the box from the top, and by means of a hinged door (not shown) at the front, may be had without disturbing the assembly of parts because of the orderly arrangement thereof.

In the device described, there are three electric circuits, shown diagrammatically in Figure 2. In the first circuit, a known potential is set up by an ordinary dry cell 29 of one and one-half volts acting through fixed resistances 30 and 31 in series with two potentiometers 32 connected in parallel and manipulated by the knobs 18.

The fixed resistances 30 and 31 are of twenty ohms and two ohms respectively, and the two potentiometers 32 are each twenty ohms. The millivoltmeter 27 is connected commonly across the terminals of the potentiometers 32 at the binding posts 33 and 34. The millivoltmeter which has proved highly useful has a double scale, the

lower scale reading to three hundred millivolts and the higher scale reading to twelve hundred millivolts. When the high range scale is to be used, the positive lead of battery 29 is transferred to the binding post 35 at the extreme right of the panel 36, thus cutting out the twenty ohm resistance 30. The electric circuit just described is completed through the metal lining 12 of the cabinet to which one side of the potentiometers 32 and one side of the battery 29 are grounded. The binding post 34 is also grounded to the lining of the cabinet so that the millivoltmeter will read the voltage drop across the potentiometers 32.

In another circuit including the leads 37 and 38, Figure 2, one pair 39 of the electrometer quadrants, Figure 3, is brought to approximately twenty-two volts above ground and the other pair 40 to about twenty-two volts below ground by means oi blocks of B".and C batteries, 41 and 42, acting through the high insulation switch ill) shown in detail in Figures 8, 7 and 8. This switch is capable of charging the quadrants and the electrometer needle 43 or grounding them as desired by the operator. Grid leaks 44 and 45, Figure 2, are mounted on the high insulation switch to prevent damage to the electrometer by limiting the flow of current in case of a short circuit thereacross.

The C"- batteries are included in the twentytwo volt battery blocks 41 and 42 so that they may be removed and replaced to change the potential of the electrometer quadrants by reasonably small units. It has been found convenient to connect a one thousand 'ohm rheostat (not shown) of the potentiometer type across a C battery (not shown) that is connected between the battery blocks 41 and 42. to place the singlepole switch 46 at one side of this parallel arrangement of the battery and rheostat and to connect the contact arm of the rheostat to the ground in place of the ground connection shown. In this way, the relative voltages impressed on the two sets of electrometer quadrants may be adjusted more delicately than by inserting or removing units of C batteries.

The third circuit includes the electrometer needle 43, (see Figure 3) and the glass electrode set-up. The needle 43 is connected to a singlepole double-throw switch 47, Figures 2, 6 and 7, having a movable arm 48, so that the needle 43 may be connecigldirst directly to the ground, and then to the ground through a' series connection with the glass electrode system. Although this circuit appears to join the circuit heretofore termed number one, which contains the dry cell 29 and the variable resistances 32, the E. M. F. of this third circuit opposes that of the first circuit. Therefore, if the voltages drop across the potentiometers 32, caused by the current flowing in the first mentioned circuit, is equal and opposite to the voltage of the electrode system, the position of the needle remains unchanged from that assumed when it is connected directly to the ground.

The high-insulation switches before mentioned, and shown schematically in Figure 2, are really combined into one switch with three flexible arms 48, 49 and 50, see Figures 6, 7 and 8.

A base 51 for the switch is made from a heavy bakelite sheet and is mounted on the shield cabinet 10 by means of studs 52 and screws 53. The studs 52 are made of a material adapted to insulate the base from the metal wall of the cabinet. The spring metal strip 48, shown at the lower left in Figure 6, is securely held beneath the heads of bolts 54 and 55 encased in tubular pillars 56 of quartz that may be cemented in the bakelite plate 51 with litharge or other cement. The other end of screw 54 serves as a binding post to which is connected a flexible conductor 57 leading to the electrometer needle. This strip 48 carries at its extended end two tungsten contact points 58 and 59, the first of said points firmly touching a similar contact 60 attached to the end of a rod 61 that extends through another quartz pillar 56. A firm contact between the points 58 and 60 is so important that a special adjusting screw 62 is provided so that the tension of the spring 48 may be regulated. To the other end of the rod 61 is attached a lead 63 connecting terminal 64 of the calomel cell 65. If the binding post 54 is electrically connected to the electrometer needle 43 and contact 60 is electrically connected to the glass electrode system through the calomel cell 65, the electrometer needle will of any electric charges.

be charged to the potential developed by the glass electrode set-up when contacts 60 and 58 are together.

The other contact 59 attached to strip 48 opposes, but does not normally touch the contact 66 on the end of a shorter spring-metal strip 67 mounted on a metal bridge 68. A flexible metal strip 69 is also connected to the metal bridge 68, see Figure 7. This bridge 68 is permanently grounded to the metal shield of the box by a metal strip 70.

When the button 19, which projects outside of the wall 10 of the shielded box, is pressed inwardly, the rod 71 that is free to move in the metal sleeve 72 displaces the strip 67 'so that contact 66 touches contact 59 concurrently to separating contacts 58 and 60. This establishes a direct ground connection to the needle 43 to relieve it When the pressure on button 19 is removed, contacts 58 and 60 come together again, the ground connection is broken and a charge is restored on the-electrometer needle. Thus, at the will of the operator, 9. charge can easily be placed on the electrometer needle or removed therefrom.

The circuit just described comprises strip 48, which is the uppermost of the three parallel strips 48, 49 and 50, as illustrated in Figure 7. In Figure 7 it can be seen that strips 49 and 50 are adapted to be commonly pressed by the spring strip 69 to be connected to the grounded bridge 68. This double spring strip 69 is manipulated by the push button 20.

The spring strips 49 and 50 are anchored at an end in the same manner as is the strip 48. Quartz bushings 56 are adjacent theanchored ends of the strips 49 and 50, there being rods 75 and 76 within the bushings and in electrical contact with the strips. Circuit legs 77 and 78 connect the rods 75 and 76 to the binding posts 79 and 80 of the electrometer and hence independently to the pairs of quadrants in the electrometer.

The switches comprising strips 49 and 50 are manipulated for charging and discharging the quadrants of the electrometer in the same manner as is the switch for charging and discharging the electrometer needle. Normally the free end of the contact strip 50 is in contact with the positive electrode 81 of one group of B batteries 41 while the contact strip 49 is in contact with the negative electrode 82 of the group of 3" batteries 42, the positive and negative charges of the batteries being, therefore, spread on the two pairs of quadrants 39 and respectively. The electrodes just designated by the reference characters 81 and 82, shown schematically in Figure 2, are mounted on the switch base 51 similarly to the contact point or electrode 60.

Pressure on the button 20 will ground the strips 49 and and consequently the electrometer quadrants to remove the electric charges therefrom. The high resistance grid leaks 44 and 45 are connected in series with electric circuit including the electrometer quadrants to prebrackets 8'7 and are for the support of the calomel cells 65 and 91; the brackets 88 and 89 are for the support of the vials 92 and 93 in which the glass electrode proper 94 is immersed. In each of the four brackets, the connecting arm to which the supporting cup is attached is made 'of quartz, thus effectively insulating the glass electrode from the metal. box upon which the tripod rests. The calomel cells 65 and 91 are identical. Their structure is shown in detail in Figure 2. 7

In the bottom of each of the calomel half cells is a layer of mercury 115. Above the mercury are layers of calomel paste and saturated calthe tip extends into the vessel 92 containing saturated potassium chloride solution 101. In this way the sample within the tube 94 is completely set apart from the external fluid 99 by the thin walls of the capillary tube while contact of the sample is established with the solution 101. The result is the separation of sample and reference buffer by a glass membrane which is the wall of the capillary tube, and the formation of an electrical potential across said membrane.

Thus, it is manifestthat an electric cell is set up. The E. M. F. developed between terminals 64 and 102 by the two half-cells acting through cium chloride denominated by the reference fi e glass electrode 94, when an unknown liquid characters 116 and 117 respectively. An apertured stopper 118 is inserted in the mouth of the calcium half cell vessels, the apertures accommodating bridges 95 and 96 and the electrodes 64 and 102. The bridges 95 and 96 extend only far enough into the vessels to reach the calcium chloride for making electrical contact therewith, the electrodes, however, extend to the bottom of the vessels where an effective contact with the mercury is insured by flattened sections 119. Flattehed sections 119 are pr ferably made of platinum. Glass rods 120 en elop the metal electrodes 64 and 102 toinsulate t ein from the half cell layers 116 and 117.

The calomel half cells 65 and 91 are electrically connected to the solutions in the glass electrode vials 92 and 93 by glass bridges 95 and 96 containing either a liquid potassium chloride solution or the usual potassium chloride and agar agar filler. If desired, simpler half cells with an acid buffer and quinhydrone in place of the calomel and mercury may be used.

The structure of the glass electrode will next be described. A thin walled soft glass test tube is used to prepare a capillary tube 94 having a bore 97 not over one-half millimeter in diameter. The thickness of the wall of the capillary tube will usually average about twenty microns. The ratio of the wall thickness to the bore diameter is substantially that of the original tube. The volume of the capillary tube is usually one-hundredths cc. or less.

The electrical resistance of the electrode or the wall of the tube 94 is several hundred megohms. The use of special glasses that have been found particularly adapted for preparing other types of glass electrodes would tend to diminish this value. Because a satisfactory resultmay be had from capillary tubes drawn from soft glass tubes, it is unnecessary to employ special glasses for all ordinary work performed with the device underdiscussion.

The tube which is but a few centimeters long may be bent into the shape of an exaggerated s, as shown in Figure 4. No difficulty arises in making the necessary bends if the glass is first softened by heat. A small electric heater is useful for this purpose. Sharp bends are to be avoided, for if they are avoided, the capillary is practically immune from breakage. The capillary sections readily fill themselves when brought in contact with the sample of the material to be tested. makes possible the collection of a fraction of a drop of the sample in a manner to avoid the transfer of other material and hence contamination of the sample of the fluid.

After the tube 94 is filled with a sample of solution to be tested it is placed so that the bend at 98 rests within the reference fluid 99 while is contained in the latter, .will be different from the E. M. F. developed when either the reference phthalate solution, or a different unknown liquid is contained in the capillary. These differences in potential may be observed by reading the millivolt meter for each change of liquid at the time a balance is obtained between the potential across the potentiometer and the potential developed by the electrode system. The glass wall of the tube 94 separating the liquids has such a high resistance that only minute currents can float therethrough. It is for this reason, as well as for the reason that should any appreciable current be taken from the cell the potential thereof would be altered, that the very sensitive electrometer and potentiometer system is necessary for the measurement of the potential of this cell. i

In making a determination, the capillary tube 94 is first filled with a solution of known acidity and the resulting electromotive force in the glass electrode assembly determined.

A convenient solution for this reference solution is M/20 normal solution of potassium acid phthalate. The electrode 94 is then removed, washed externally and internally dried, and filled with the unknown solution.

The electromotive force is again determined/1 and the difference between this value and that of the first.electromotive force obtained. This difference is millivolts, if obtained from the data taken when the solutions are at 25 C., and when divided by the factor 59.1 gives the difference in pH between the phthalate solution and the unknown. The factor 59.1 is taken from a previously prepared chart.

If the solution which bathes the exterior of the capillary tube is a neutral buffer, the voltage obtained with the phthalate in the capillary tube is in the neighborhood of one hundred eighty millivolts. Solutions more alkaline than the phthalate give values less than this and those more acid give greater values.

The difference in millivolts, after converting to pH by dividing by. the proper factor, is added to or subtracted from 3.98 (the pH of the phthalate solution), depending on whether the voltage obtained with the unknown is smaller or larger than the voltage set up by the phthalate solution. It follows that the voltage becomes smaller as the solution becomes more alkaline. Near the neutral point, the observed voltage is zero and beyond. this the potential increases in the opposite direction, requiring that the terminals 64 and 102 be interchanged.

A voltage so obtained is marked with the negative sign, and added to the voltage recorded between the phthalate solution and the solution bathing the capillary tube. The purpose of using the intermediate solution instead of comparing the unknown and phthalate solutions directly by placing the phthalate in the cup is the elimination of sources of error. It is essentially a method of substitution. In the process of taking differences any constant errors which appear in the observed voltages will disappear, or be automatically cancelled. These errors are such as an inaccurate zero setting of the voltmeter, inequality of the two calomel half cells or liquid junction potentials at the half cells.

To determine the voltage of an unknown system with the apparatus shown schematically in Figure 2, the switch 103 which is connected to the dry cell29 and the switch 46 are closed. The millivoltmeter 27 then assumes a position which may be varied by adjusting the potentiometers 32. The double- pole switch arms 49 and 50 are momentarily thrown to ground by pressing the button 20. This relieves the quadrants of the electrometer of any electric charge. When the button 20 is released, the quadrants are connected to the battery blocks 41 and 42 for a recharge.

The needle of the electrometer grounded by pressing the push button 19 for depressing the grounded contactor 66 against the contaotor 59. Whilethe electrometer needle is grounded, and hence at zero potential, the position of the needle image on the scale in the eyepiece of the microscope is noted.

Upon releasing the spring strip 67, the needle 39 of the electrometer is automatically connected through the post 61 with the electrode system, which is in series with the known voltage across the potentiometers 32 and the ground. unknown voltage of the electrode system which is in opposition to the potential across the resistance 32 does not cancel that known voltage, as measured by the millivoltmeter 27, the net unbalanced voltage causes the electrometer needle to take another position. The resistance 32 is then adjusted until the voltage drop thereacross, due to the current from the battery 29, is-just equal and opposite to the potential of the electrode system.

When this is accomplished, there will be no de- :fiection of the electrometer needle when the grounded contactor spring er is removed from the spring 48 to permit the spring id to again become electrically connected with the electrode 60 because the electrode 6G is at that time at ground potential. The voltage of the electrode system is at this time equal to that shown on the millivoltmeter scale. The sensitivity of the electrometer is such that the voltage may be easily adjusted to one half millivolt. Using a 16 MM objective and a 15m: ocular, a sensitivity of ten eyepiece divisions for an electromotive force of thirty or forty millivolts is possible.

The sensitivity of the electrometer increases as the potentials imposed on the quadrants of the electrometer approach the critical values furnished by the makers of the instrument.

The main object of this type of glass electrode has been to obtain a rugged and compact electrode assembly rather than to investigate the nature of the glass electrode. No effort has been made to determine the limitations of glass electrodes. In keeping with the effort to obtain a rugged and sturdy piece of apparatus, the apparatus herein described was, on one occasion, transported for several hundred miles in an automobile. Within one hour after the completion of the journey, the apparatus was set up and accurate measurements made therewith.

is next.

If the Another important feature of the invention is the ingenious arrangement of the electrical system so that all external rheostat knobs and switches are grounded to themetal wall or lining of the cabinet so that the potential thereof will not be changed when touched by an operator. Hence, this very sensitive apparatus is unaffected by the operator in the process of taking measurements. The hands of the operator naturally rest on the box and .do not introduce to the systern any undesired electrical charges.

What is claimed as new and is desired to be secured by Letters Patent of the United States is:

1. For use with a device for determining the ion concentration of a solution, an electrode comprising a capillary tube of a dielectric material and containing the solution during such determination.

2. For use with a device for determining the hydrogen ion concentration of a solution, an electrode comprising a glass tube of dimensions to draw such solution therein by capillary action and containing the solution during such determination. v

3. For use with an apparatus for determining the hydrogen ion concentration of a solution, an electrode comprising a capillary tube of dielectric material containing such solution, a second solution in contact with only the exterior walls of said capillary tube, a support for said electrode and said solutions, and means for insulating said electrode and said solutions from said support.

4. An apparatus for determining the hydrogen ion concentration of a solution comprising the combination of a cell having a capillary tube of dielectric material enclosing such solution, a ves sel containing abody of saturated potassium chloride solution, a second vessel containing a body of reference solution, a section of the exterior of said capillary tube being in electrical contact with the body of reference solution and an open end of said tube extending into said body of rive-semen: chloride, the potassium chloride solution and the reference solution being of opposite polarity in said cell, a source of electrical energy, means for ascertaining the potential of said source of energy, means for modifying the potential of such source, electrical conductor means connecting the reference solution to the side of said source of energy of like polarity, and means for detecting equalization of the potential of the body of potassium chloride solution and or the other side of said source of energy.

5. In an apparatus for determining the hydrogen ion concentration of a solution, 'a cell comprising a capillary tube of dielectric material containing the solution under determination, a vessel containing a body of electrical conductor solution, a second vessel containing a body of reference solution, a section of the exterior of said tube being in electrical contact with the body of reference solution and an open end of said tube extending into the body of electrical conductor solution, said bodies of conductor solutionand reference solution being terminals of opposite polarity of said cell, in combination with a source of electrical energy of variable potential, means for changing the potential of said source of energy, means for ascertaining the potential of said source of energy, electrical conductor means connecting said body of reference solution to said source of energy at the side of like polarity, means for detecting when said body of electrical 'shaped bend therein for immersion in a conductor solution and the other side of said source of energy are of the same potential.

6. Apparatus for determining the hydrogen ion concentration of a solution and comprising a capillary tube of insulating material containing such solution duringdetermination of the ion concentration thereof, said tube having a U- reference solution.

'7. An apparatus for determining the hydrogen ion concentration of a solution and comprising the combination of a cell having a capillary tube of dielectric material enclosing such solution, a vessel containing a body of saturated potassium chloride solution, a second vessel containing a body of reference solution, a section of the exterior of said capillary tube being in electrical contact with the body of reference solution and an open end of said tube extending into said body of potassium chloride,\the potassium chloride solution and the reference solution being of opposite polarity in said cell, a standard half cell, a conducting bond of potassium chloride solution between the saturated potassium chloride in the first vessel and said half cell, a second standard half cell of potential equal to that of the first half cell, a conducting bond of potassium chloridesolutionbetween the reference solution in said second vessel and said second half cell, the whole cell thus formed providing for a given observation an invariable source of electromotlve force, and a second source of electromotive force opposing said first source, means for ascertaining the potential of said second source of electromotive force, means for modifying the potential of said second source, electrical conductor means connecting said second half cell to the side of like poiarity of said second source of electromotive force, and means for detecting equalization or the potential of said first half cell and of the other side of said second source of electromotive force.

WILLIAM J. YOUDEN.

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