US1900893A

US1900893A - Automatic silver recovery control

Info

Publication number: US1900893A
Application number: US540620A
Authority: US
Inventors: Kenneth C D Hickman
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1931-05-28
Filing date: 1931-05-28
Publication date: 1933-03-07
Anticipated expiration: 1950-03-07

Description

EXAMINER AU ZDZ LDU'ZUL FIP8212 EX fJSS KtFERENCE 1,900,893

March 7, 1933. K. c. D. HICKMAN AUTOIA'I'IC SILVER RECOVERY CONTROL Filed lay 28, 1931 2 Sheets-Sheet l gwbenfoc,

H U n m GHHidnnm 5% Xanyo Z Z O U 14 U l CROSS REFERENCE EXAMINER March 7, 1933. K c D HICKMAN 1,900,893

AUTOMATIC SILVER RECOVERY CONTROL File d Kay 28. 1931 2 Sheets-Sheet 2 WI/6111mm C (to? acemploys opposed electro-motive forces, one

Patented Mar. 7, 1933 UNITED STATES PATENT oFFIcE KENNETH O. 1). mm, OI ROCHESTER, NEW YORK, ASSIGNOR '10 EASTMAN KODAK COMPANY, OF ROCHESTER, NEW YORK, CORPORATION OF NEW YORK AUTOMATIC SILVER RECOVERY CONTROL Application fled Kay 28.

My invention relates to an automatic silver recovery control and more particularly to an automatic control which regulates the plating current during electrolysis correspond ing to theplating ion concentration and rate of flow of the electrolyte and in accordance with the existing plating current.

The present invention has been developed with particular attention to the recovery of silver from a used photographic fixing solution by electroplating, which recovery requires a veryprecise and accurate control of the plating current in order to secure efliciency of operation and freedom from occasional failure.

The invention is particularly applicable to the method and apparatus for electroplating silver from used photographic fixing solu-. tious by electrolysis disclosed in the copending applications of Hickman and Weyerts Serial No. 540,622, filed May 28, 1931, and of Hickman and \Veyerts, Serial No. 510,621, filed May 28, 1931, respectively.

j The maximum safe current for plating the solutions contemplated is determined by the product of three variables, the plating ion or silver ion concentration of the solution, the rate of flow of solution through the apparatus and the plating capacity of the apparatus. In a permanent installation and with any particular type of plating cell the plating capacity is determined once and for all so that this variable becomes a constant and it remains necessary to devise apparatus for determining the other two variable factors at frequent intervals and continuously during operation.

' The primary object of my invention is the provision of an automatic control for the plating current of an electroplating appa ratus.

Another object of my invention is the pro-- vision of such an automatic control which regulates the plating current according to the plating or silver ion concentration of the electrolyte.

A further object of my invention is the provision of such an automatic control which corresponding to the plating ion concentra- 1931. Serial no.

tion of the'electrolyte and the other to the existing plating current and rate of flow of electrolyte, so that the plating current is increased ordecreased depending on the dominant electro-motive force.

Still another object of my invention is the provision of an automatic control for the plating current of a silver thio-sulfate electroplating apparatus which utilizes the optical covering power of colloidialeilver sulfide in a colorimeter to control an electromotive force in a Wheatstone bridge.

A still further object of my invention is the rovision of an automatic control which utilizes an electro-motive force from a shunt in the plating current circuit to oppose an electro-motive force from a bolometer, a' contacting galvanometer being moved to one of two posltions depending on which rof said electro-motive forces predominates.

Another object of my invention is the provision of a plating current control means in turn controlled by a contacting galvanomeier included in a control circuit containing 0 posed'electro-motive forces.

With'these objects in view, the present invention consists in certain features of novelty in the construction, combination and ary rangement of parts by which the said objects and certain other objects are effected all as fully described with reference to the accompanying drawings and more particularly pointed out in the claims.

Like reference numerals designate similar eiements in the accompanying drawings wherein: p 4

Figure 1 illustrates more or'less diagrammatically the preferred form of my automatic electroplating control means.

Figure 2 illustrates also diagrammatically a modification of the means 1n the control apparatus for impressing an electromotive force on a control circuit which corresponds to the plating or silver ion concentration of the electrolyte.

Throughout the remainder of this 5 'fi. cation, the expression electro-motive iorce will be shortened to its accepted abbreviation E. M. F. The control apparatus of my invention will Parts Hypo 300 Sodium sulfite 10 Alum 20 Acid 5 Silver halide 10 Upon observation of the above composition of a used fixing solution, the variation of the conductivity with the silver concentration and of the silver electro-potential with the silver concentration seemed to present the most feasible methods of attack for controlling the plating current of the apparatus according to the silver concentration. However, neither of these methods have proved of any practical importance. Consequently, I have resorted to employing the optical covering power of silver sulfide and the plating rate of the silver ion corresponding to the silver concentration of the solution. These principles are embodied in my preferred and modified form of automatic control, respectively.

The electroplating apparatus which is to be controlled according to the present invention is composed of 'many well-known elements. The plating cells 10 have electrodes 11 which are connected alternately to opposite sides of a direct current generator 12. A variable shunt 13 is located in the circuit to the electrodes .11 and its function will be described hereinafter.

A field rheostat 14 is placed in one leg of an unidirectional source of electrical energy which is connected to the field windings of generator 12. The generator 12 is rotated in a known manner by any suitable prime mover such as a motor. The field excitation of the generator 12 may be varied by increasing or decreasing the portions of field rheostat 14 which are in the circuit to decrease or increase the current output of the generator. The movement of field rheostat 14 is accomplished 'by employing a split wound or reversible motor 15 which actuates a contactor arm 16 making contact withopposite points of the field rheostat 14 to increase or decrease the resistance thereof as required.

A wire 17 connects the center tap of motor 15 to one leg of an alternating current source while the other leg of the alternating current source is connected by a wire 17 to the contact 18 and armature 23 of

relays

20 and 21, respectively. A wire 19' connects one side of motor 15 to contact 19 of relay 21 and a wire 22 connects the other side of motor 15 to armature 22 of relay 20. Consequently, when relay 21 is energized, armature 23 is attracted and makes contact with contact 19 to complete the circuit from the source of alternating electrical energy through one winding of motor 15 and rotates the same in a clockwise direction as view from Figure 1. Also, if relay 20 is energized, a rmature 22 is attracted to complete the circuit through the other winding of motor 15 and rotate the same in a counterclockwise direction.

The coils of

relays

20 and 21 are energized by low voltage alternating current circuits through

trickle chargers

24 and 25 which are in turn energized by the aforementioned source of alternatin current energy and which are controlled by a set of

contacts

26, 27 and 28 on a contacting galvanometer 29.

The complete assembly above described, excluding the contacting galvanometer but including the contacts thereof, comprises the plating current control means referred to in the claims.

The supply of electrolyte, such as a used or exhausted photographic fixing solution, to the plating cells 10 will now be described. The solution is conducted from any suitable source to a filter box 32 by a pipe 33. The so lution will pass through a plurality of holes 34 in said filter box 32 and through any suitable filterin means such as a plurality of felt socks (not s own) and is discharged through a wier 35 into a box 36. A pipe 37 leads from box 36 to the ends of the plating cells 10. The electrolyte or hypo solution is withdrawn from the center of plating cells 10 by means of discharge pipes 38. The conduction of the electrolyte to the cells 10 and filtering of the electrolyte may be accomplished in any other suitable manner which includes a wier and the apparatus here described for that purpose is only by way of example.

There is a maximum plating current which the plating cells will carry for any particular silver content of solution. It may be arranged to su ply this maximum current when the solutlon flow is also at a maximum; then for any lesser rates of flow at this concentration proportionall less current will be needed to deplete the ath of silver. Examples will make the point clear. Suppose used fixing solution containing 6 grams of silver per liter is flowing at 20 liters per minute, requiring 1500 amperes for removal of the metal, 1500 amperes being the maximum safe current and 20 liters a minute the atest flow ever encountered; then, when the flow falls to 10 liters per minute 750 amps.

will be suflicient. and at liter per minute not more than 75 amps. should be passed. Similarly, solution containing only 2 grams per liter cannot tolerate more than 500 amperes in the same apparatus at liters a minute flow, and this must be cut to 50. amperes at 2 liters a minute. The adjustment is made automatically by using a variable shunt which is operated by a flow meter.

The flow meter includes wier and a float box 39 which is fastened to filter box 32 at the same level as box 36, being connected hereto by means of a pipe 40. The wier 35 is cam shaped so that the level in box 36 rises in direct relation to the rate of flow, the same level also existing in float box 39. A hollow, hard rubber float 41 is mounted on an arcuate arm 42 fulcrumed to the float box 39 at 43, while the variable shunt comprises a contacting arm 44 carried on and insulated from arcuate arm 42 and making contact with a plurality of copper segments 45 which are held before contacting arm 44 by means of a bracket 46 attached to the float box 39. Individual wires are attached to each of the segments 45 to form a cable 47 leading to the shunt 13, the other ends of these individual wires being successively connected at intervals spaced longltudinally along shunt 13 so that movement of contact arm 44 in a clockwise direction will decrease the effective length or potential drop of the shunt 13. A flexible wire 48 extends from the contact arm 44 to one side of the coil in contacting galvanometer 29.

The function and purpose of the flow meter and variable shunt just described will be more fully developed in the explanation of the operation of my control apparatus.

The automatic control means according to my invention is completed in its preferred form by a bridge resistance means a siphonic mixing means and an illuminatmg means.

Resistances

49 and 50 form two arms of a Vheatstone bridge with their juncture 51 connected to one side of shunt 13 by a wire 56, while their opposite extremities 52 and 53 are connected through switch 54 to a battery 55. The other two arms of the Wheatstone bridge are formed by the elements of a bolometer comprising a glass bulb 57 enclosing a pair of nickel elements or

cones

58 and 59.

Said

cones

58 and 59 should have a resistance of at least 100 ohms and may be made up of #40 pure nickel wire covered with a thin coating of bakelite varnish and wound conveniently into a 90 cone till a resistance of 150-160 /ohms has been attained. The element is then covered with cellulose acetate dissolved in a solvent which does not soften the bakelite, is allowed to dry and is stripped from thesupport. The

cones

58 and 59 are mounted within bulb 57 with their apeces adjacent each other, the base of element 58 being adjacent a mica window 60 in one end of bulb 57 to eliminate drafts on element 58. The

apeces of

cones

58 and 59 are connected to each other and to one side of the coil of con-.

tacting galvanometer 29 by a wire 61, the base edges of

cones

58 and 59 being connected to extremities 5:2 and 53 of the

bridge resistances

49 and 50 by

wires

62 and 63, respectively.

The siphonic mixing means includes a flask 67 which has a siphon tube 68'attached to the bottom thereof and which is supplied with water through a pipe 69 regulated by a valve 70 and overflowing to a waste through pipe 71. As a matter of hydraulics it is well established that, when the level of water in flask 67 increases to such a height that the upper elbow of siphon tube 68 is filled, the whole quantity of water will be siphoned or drawn out of flask 67.

A constant level bulb 72 is intermediately connected to siphon tube 68 by a capillary tube 73. A bottle 74 contains a suitable quantity of sodium sulfide and has the bottom thereof connected to a pipe 7 6 extending into vessel 78. An inverted U-tube 77 extends from the top of bottle 74 to a bell jar 75 the end of pipe 76 being even with the bottom edges of the bell jar'75. The pipe 79 leads from the bottom of vessel 78 to the constant level bulb 7 '2 which has an air vent 80. Also as a matter of hydraulics, it should be apparent that the sodium sulfide from bottle 74 will be supplied to vessel 78 to maintain a definite level therein. By virtue of the connection through pipe 79. the constant level bulb 72 will have ailevel of sodium sulfide equal to that existing in vessel 78.

A second constant level bulb 81 is connected by a capillary tube 82 to siphon tube 68 at a point which is opposite the connection of tube 73 to tube 68. A pipe 83 extends from the bottom of box 36 to constant level bulb 81 and contains a valve 84. The box 36 is preferably located at a higher level than bulb 81 so that electrolyte or used fixing solution will flow by gravity from box 36 and its introduction into bulb 81 may be controlled by valve 84. Bulb 81 is also provided with an overflow pipe 85 so that although the solution is constantly flowing through bulb 81 its level will never exceed that of pipe 85. An air vent 86 is attached to the top of bulb 81.

1 A receptacle 87 is placed below the lower end of siphon tube 68 and is connected by a pipe 88 to a colorimeter tube 89 which has an air vent 90 and an outlet pipe 91. Receptacle 87 is preferably located above the level of outlet pipe 91 so that solution can flow from the receptacle 87 to the colorimeter tube 89 by gravity. The colcrimeter tube 89 is cylindrical in form and is located with its ends parallel to the mica window 60 of the bolorneter. A branch pipe 92 with a valve 93 leads from the water supply pipe 69 into the receptacle 87.

The operation of the siphonic mixing QUU of contactin means and colorimeter will now be explained. It has been established that the 0 tical covering power of colloidal silver sul de solutions can be duplicated with accuracy if the conditions of precipitation and the age of the solution at the time'of viewing are kept uniform. The conditions are simple, involving little more than rapid mixing in the presence of a small amount of gelatine and certain quantities of electrolyte, both of these latter materials being provided with sufiicient accuracy by the used fixing solution itself. As previously stated, the

constant level bulbs

72 and 81 are filled to definite levels representing the proper proportion to each other for precipitation of silver sulfide in the solution resulting from the mixture of sodium chloride and used fixing solution. A constant level is maintained above the valve by the water supply, said valve 70 allowing a small, approximately regular, trickle to fill the flask 67 until the upperbend in the siphon tube 68 is filled and a unit volume of water flows through tube 68. The volumes of water, flowing periodically through tube 68 under such conditions, vary only by extremely small amounts in volume from each other. The unit volume of water which flushes through the siphon tube at regular intervals creates a vacuum within capillary tubes 73 and 82 and acts to draw the sodium sulfide from bulb 72 and the fixing solution from bulb 81 so that all are mixed in the siphon tube 68 or ultimately in the receptacle 87. A bafile plate 94 is positioned within receptacle 87 to break the force of the solution entering the same. Obviously, the mixed solution now contains an opaque precipitate proportional to the plating ion or silver concentration in the fixing solution and is conducted by gravity into the colorimeter cell 89, from which it is conducted to waste by the overflow pipe 91.

The illuminating means, which functions in conjunction with the siphonic mixing means and bolometer,-consists of an incandescent lamp 95 located in a housing 96 in front of a mirror 97 and having a filament 98 radiating light which passes directly and by reflection through a condenser 99, through colorimeter cell 89, through mica window 60, and into the interior of the bolometer cone 58.

The complete function of the preferred form of my control apparatus will now be described: i a

Preliminary to operation of the control apparatus valve 70 water supply is opened so that pure water flows through the colorimeter cell '89. The

resistance arms

49 and 50 of the Wheatstone bridge are balarced so that contact arm 27 galvanometer 29 assumes a neutral position between

contacts

26 and 28 and so that the bridge resistance means is balanced with maximum illumination on is closed and valve 93 of the bolometer element 58. The electrolyte is now is now passed through the filter box 32 into the plating cells and the plating current is applied to the cells 10. The positions of valves 7 0 and 93 are reversed and the siphonic mixing means functions as previously described to introduce a solution into the colorimeter which varies in opacity according to the plating or silver ion concentration in the electrolyte. The illumination on the interior of bolometer cone 58 will be reduced in proportion to the opacity of the solution in the colorimeter to correspondingly reduce the resistance of bolometer cone 58 and unbalance the Wheatstone bridge so that an E. M. F. is impressed upon a control circuit including the contacting galvanometer 29.

At the same time the float 41 has assumed a position corresponding to the level of electrolyte in box 36 and contact arm 44 has taken a definite position with respect to the segments 45 so that a certain portion of the variable shunt 13 is in the control circuit. The potential drop along the variable shunt 13 will also depend upon the value of the plating current determined by the position of field rheostat 14. Consequently, the E. M. F. which is imposed on the control circuit including contacting galvanometer 29 in opposition to eter is a function of the rate of flow of electrolyte and the existing plating current for the latin cells 10.

I? the M. F. from the bolometer predominates indicating that the plating or silver ion concentration of the electrolyte has increased and requires more plating current, the

contacts

27 and 28 of the contacting galvanometer will make. Relay 20 will be energized, armature 22 will be magnetically drawn to contact 18 and motor 15 will rotate in a counter-clockwise direction to decrease the resistance of field rheostat 14 and increase the field excitation for generator 12 so that more plating current is applied to the cells 10. Also, if the rate of flow of electrolyte is decreased with any specified plating current still existin the float 41 will be lowered to make the variable shunt 13 efl'ectively longer with ail/increase in the E. M. F. 'in the control circuit which is in opposition to the E. M. F. of the bolometer. The E. M.- F. from the shunt means will now predominate causing

contacts

26 and 27 of the contacting galvanometer to make, energizing relay 21, drawing armature 23 to contact 19 and rotating the motor 15 in a clockwise direction to increase the resistance of field rheostat 14 and decrease the field excitation of generator 12 so that the plating current is reduced.

In case the concentration of the plating or silver ion in the electrolyte should decrease, then the precipitate or opacity of the solution in the colorimeter would also decrease. Whereupon the resistance of bolomthe E. M. F. set up by the bolometer element 58 would be increased and the electro-motive force in the control circuit from the variable shunt would predominate to make

contacts

26 and 27 of the contacting galvanometer 29 and to result in the decrease of the plating current to the cells 10 as just described in detail above.

It is now apparent that the operation of the control apparatus according to my invention is fully automatic, inasmuch as the plating current for the electroplating apparatus is varied in the proper direction and in proper proportion with variation in the plating or silver ion concentration of the electrolyte and rate of flow thereof through the plating cells.

The means for impressing an E. M. F. corresponding to the plating ion concentration on the control circuit may alternatively be made up of a resistance bridge means which utilizes the precision with which the plating ion is deposited by electrolysis according to the ion concentration of the electrolyte. Although other forms of so impressing an E. M. F. on the control circuit are deemed to be within the scope of my invention, I have found that one arm of the resistance bridge means may be formed by a continuous wire from an auxiliary plating cell.

The auxiliary plating cell includes a container 100 having an inlet pipe 101 which is supplied with a flow of electrolyte from a pipe such as 83, said container 100 also having an outlet or overflow pipe 102 discharging electrolyte to waste. A hollow anode 103 is mounted within container 100 and connected through a variable resistance 104 to the positive side of a battery 105. The cathode of the auxiliary plating cell is formed of a continuously moving high resistance wire 106 such as a nichrome wire. A reeling means including a spool 107 contains a coil of high resistance wire 106 and is rotatably mounted. The wire 106 extends through the hollow cathode 103, through the electrolyte within container 100 and over a pair of spaced

contacts

108 and 109 to any suitable winding means 110, such as a telechron motor. The speed at which the winding means 110 draws the high resistance wire 106 through the elec-, trolyte and hollow anode 103 of the auxiliary plating cell .is approximately one to two inches per minute. The battery 105 has its negative side connected to contact 108 by a wire 111. A pair of resistance arms 112 and 113 are connected together at 114 and across the battery 105. A third resistance-arm 115 is connected to the battery 105 and

resistance

113 and 116, while the other end of resistance 115 is connected to contact 109.

This entire apparatus is adapted to replace the siphonic mixing means, colorimeter and bolometer of the preferred modification. wire 117 leads fr Wheatstone. bridge to one side of the shunt 13 s. om the point 114 of the in the plating circuit from the direct current generator 12 and a wire 118 extends from the opposite point of the Wheatstone bridge 119 to the side of the contacting galvanometer 29 previously connected to the bolometer.

The operation of the modified form of automatic control for electroplating apparatus is as follows:

The Wheatstone bridge is first balanced by variation of the

resistance

112, 113 and 115 so that there is no deflection of the galvanometer 29 when bare high resistance wire 106 extends between

contacts

108 and 109. This balancing of resistances should be accomplished when pure water is flowing through the container 100 instead of used photographic fixing solution from the pipe 83. The drawing power of most electrolytes and especially silver thio-sulfate solutions, is so great that small cathodes in uniformly stirred solutions build up adherent deposits at a rate which varies directly with the plating or silver ion concentration of the electrolyte. Thus with variation of the plating or silver ion concentration of the used photographic fixing solution corresponding deposit is made upon the high resistance wire 106 to vary the conductivity thereof in proportion to the plating or silver ion concentration of the electrolyte.

If the silver ion concentration is increasing, indicating the need for a greater plating current at the cells 10, the conductivity of the portion of wire 106 between

contacts

108 and 109 is proportionately increased. This sets up an E. M. F. in the control circuit which predominates over the E. M. F. from the shunt means and causes deflection of the contacting galvanometer 29 to make

contacts

27 and 28 with consequent rotation of motor 15 in a counter-clockwise direction and increase in the field excitation of plating generator 12. Conversely, if the plating or silver ion concentration of the electrolyte decreases, then the conductivity of the bridge arm between contacts 108 and 109'will also decrease to decrease the E. M. F. in the control circuit and allow the E. M. F. from the variable shunt to predominate and to deflect galvanometer 29 so that

contacts

26 and 27 are made to decrease the lating current given out by generator 12. fn this modified form of the control apparatus, as well as in the preferred form,there is a clash between the E. M. F. set up by variation of the platin or silver ion concentration and the E. M. which is a junction of the existing plating current and the rate of within the control circuit which includes the coil of the contacting galvanometer 29, the cable and wire. to the variable shunt means flow of electrolyte and. the connections to the Wheatstone zooments, it is obvious that anyone of these elements may be replaced within the combination by an equivalent without exceeding the scope of the invention. Therefore, the disclosure or description of my invention is to be construed in an illustrative sense and limited only by the scope of the appended claims.

Having now particularly described my invention, what I claim and desire to secure by Letters Patent of the United States is:

1. In an automatic control for an electroplating apparatus adapted to receive an electrolyte, the combination with a plating current control means adapted to vary the plating current supplied to said apparatus, and a control circuit for said plating current control means, of means for impressing an electro-motive force corresponding to the plating ion concentration of the electrolyte on said control circuit, and a shunt means for impressing an opposed electro-motive force corresponding to the plating current on said control circuit, whereby the plating current is varied directly with the plating ion concentration of the electrolyte.

2. In an automatic control for an electroplating apparatus adapted to receive an electrolyte, the combination with a plating current control means adapted to vary the plating current supplied to said apparatus, and a control circuit for said plating current control means, of a resistance bridge means including balanced resistance arms, a means for varym the resistance of one of said arms correspon ing to the plating ion concentrat1on of said electrolyte to im ress an electromotive force on said contro circuit, and a shunt means for impressing an opposed electro-motive source on said control circuit corresponding to the plate current whereby the plating current is increased or decreased with increase and decrease in the plating ion concentration of the electrolyte.

3. In an automatic control for an electroplating apparatus adapted to receive an electrolyte, the combination with a plating current control means adapted to vary the platmg current supplied to said apparatus, and a control circuitjor said plating current control means, of a shunt means for impressing an electro-motive force on said control circuit corresponding to the plating current and rate of flow of electrolyte, including a variable shunt and a flow meter for varyin the same, a bridge means including balanced resistance arms connected to said control circuit and a means for varying the resistance of one resistance arm corres onding to the plat- 111g ion concentration of t e electrolyte to impress an electro-motive force on the control circuit opposed to the 'electro-motive force of the shunt means.

4. In an automatic control for an electroplating apparatus adapted to receive an electrolyte, the combination with a plating current control means adapted to vary the plating current supplied to said apparatus, and a control circuit for said plating current control means, of a shunt means for impressing an electro-motive force on said control circuit corresponding to the plating current and rate of flow of electrolyte, including a variable shunt and a flow meter for varying the same, and a bridge means including a Wheatstone l-.'idge connected to said control circuit and a means for varying the resistance of one arm of the Wheatstone bridge corresponding to the plating ion concentration of the electrolyte to impress an electro-motive force on the control circuit opposed to the electro-motive force impressed by the shunt means.

5. In an automatic control for an electroplating apparatus adapted to 'receive a tion of electrolyte, the combination with a plating current control means adapted to vary the plating current supplied to said apparatus, and a control circuit for said plating current control means, of a resistance means including balanced resistance arms, a means for varying the resistance of one of said arms corres onding to the plating ion concentration 0? the electrolyte to impress an electromotive force on said control circuit, and a shunt means for impressing and opposing the electro-motive force on said control circuit corresponding to the plating current and flow of electrolyte, including a variable shunt in said plating current control means, a wier through which the electrolyte is introduced to the apparatus and a float operating said variable shunt and moved by change in the liquid level in said wier corresponding to the rate of flow of electrolyte.

6. In an automatic control for an electroplating apparatus adapted to receivean electrolyte, the combination with a plating current generator, a plating current control means including a field rheostat for said generator, a reversible motor operating sald rheostat and a pair of relays each connecting said motor to a source of electrical energy for operation in opposite directions, and a control circuit including a contacting galvanometer having two contactin" positions and operating one relay in eacli position, of means for impressing an electro-motive force corresponding to the plating ion concentration of the electrolyte on said control circuit, and a shunt means for impressin an opposed electro-motive force corresponding to the plating current on said control circuit whereby the plate current is varied directly with the plating ion concentration of the electrol In an automatic control for an electroplating apparatus adapted to receive an electrolyte, the combination with a plating cur- 'rent generator, a plating current control DKAMINEB means including a field rheostat for said generator, a reversible motor operating said rheostat, a pair of relays each connecting said motor to a source of alternating electrical energy for operation in opposite directions, a

control circuit including a contacting gal vanometer having two contacting positions, a pair of trickle chargers connected to a source of alternating electrical energy and controlled individually by each position of the contacting galvanometer to supply low voltage alternating electrical energy to said relays, of means for impressing an electro-motive force corresponding to the plating ion concentration of the electrolyte on said control circuit, and a shunt means for impressing an opposed electro-motive force corresponding to the plating current of said control circuit whereby the plating current is varied directly with the plating ion concentration of the electrolyte.

8. In an automatic control for an electroplating apparatus adapted to receive an electrolyte,.the combination with a plating current control means adapted to vary the plating current supplied to said apparatus, and a control circuit for said plating control means, of a shunt in the plating current control means and connected across said control circuit, a Wheatstone bridge connected to said control circuit, a bolometer having a pair of nickel elements forming two arms of said Wheatstone bridge, a light source directed onto one of said nickel elements and a colorimeter therebetween and containing a solution with an opaque precipitate corresponding in quantity to the plating ion concentration of the electrolyte.

9. In an automatic control for an electroplating apparatus adapted to employ used photographic fixing solutions as an electrolyte, the combination with a plating current control means adapted to vary the plating current supplied to said apparatus and a control circuit for said plating current control means, of a shunt in the plating current control means and connected across said control circuit, a Wheatstone bridge connected to said control circuit, a bolometer having a pair of nickel elements forming two arms.

of said Wheatstbne bridge, a light source directed onto one of said nickel elements and a colorimeter therebetwen and containing a .solution with a colloidal silver sulphide precipitate corresponding in quantity to the silver ion concentration of the used fixing solution. v

10. In an automatic control for an electroplating apparatus adapted to receive an electrolyte, the combination with a plating current control means adaptedto vary the plating current supplied to said apparatus and a control circuit for said plating current control means, of a shunt in the plating-current control means and connected across said control circuit, a Wheatstone bridge connected to said control circuit, a bolometer having a pair of nickel elements forming two arms of said Wheatst-one bridge, a light source directed onto one of said nickel elements, a colorimeter therebetween and a siphonic mixing means connected to said colorimeter and preparing at intervals solutions with a precipitate of plating ion corresponding to the concentration thereof in the electrolyte.

11. In an automatic control for an electroplating apparatus adapted to receive an electrolyte, the combination with a plating current control means adapted to vary the plating current supplied to said apparatus and a control circuit for said plating control means, of a shunt means impressing an electro-motive force on said control circuit corresponding to the plating current and a resistance bridge means connected to said control circuit including a resistance arm of variable resistivity according to the i llumination thereon, and illuminating means directed onto said resistance arm and varying in intensity with the plating ion concentration of the electrolyte whereby an electro-motive force opposed to the electro-motive force of the shunt means is set up in the control circuit.

12. In an automatic control for an electroplating apparatus adapted to receive an electrolyte, the combination with a plating current control means adapted to vary the plating current supplied to said apparatus and a control circuit for said plating current control means, of a shunt means impressing an electro-motive force on said control circuit corresponding to the plating current and a resistance bridge means connected to said control circuit including a resistance arm of variable resistivity according to the illumination thereon,and illuminatingmeans having a light source directed onto said resistance arm and a colorimeter therebetween adapted to contain a solution varying directly in opacity with the plating ion concentration.

13. In an automatic control for an electroplating apparatus adapted to receive an electrolyte, the combination with a plating current control means adapted to vary the plating current supplied to said apparatus and a control circuit for said plating current control means, of a shunt means impressing an electro-motive force on said control circuitcorresponding to the plating current in a resistance bridge means connected to said control circuit including a bolometer having a pair of resistance elements forming two arms of the resistance bridge and made of materials having a resistivity directly proportional to the illumination thereof, and including an illuminating means having a light source directed onto one of said resistance elements and a colorimeter therebetween adapted to contain a solution varying directly in opacity with the plating ion concentration of the electrolyte.

14. In an automatic control for an electrd plating apparatus adapted to receive an electrolyte, the combination with a plating current control means adapted to vary the plating current supplied to said apparatus and a control circuit for said plating current'control means, of a shunt means impressing an electro-motive force on said control circuit corresponding to the plating current and a resistance bridge means connected to said control circuit including an auxiliary plating cell having an electrode and adapted to receive a continuous flow of electrolyte, and having a wire continuously moving as an electrode through said auxiliary plating cell and forming one arm of the resistance bridge means whereby said wire is plated to decrease the resistivity thereof and impress an opposed electromotive force on said control circuit corresponding to the plating ion concentration of the electrolyte.

15. In an automatic control for an electroplating apparatus adapted to receive an electrolyte, the combination with a plating current control means adapted to vary the plating current supplied to said apparatus, and a control circuit for said plating current control means, of a shunt means impressing an e'lectro-motive force on said control circuit corresponding to the plating current, and a resistance bridge means connected to said control circuit including an auxiliary plating cell having a hollow anode and adapted to receive a continuous flow of electrolyte and having a high resistance wire continuously moving as a cathode through said anode and forming one arm of the resistance bridge means whereby the resistivity of said arm is varied corresponding to the plating ion concentration of the electrolyte and a counter electro-motive force is introduced into said control circuit.

16. In an automatic control for an electroplating apparatus adapted to receive an electrolyte, the combination with a plating current control means adapted to vary the plating current supplied to said apparatus, and a control circuit forsaid platingcurrent control means, of a shunt in the plating current control means and connected across said control circuit, a Whcatstone bridge in saidcontrol circuit and an auxiliary plating cell having an anode and adapted to have a continuous supply of electrolyte, reeling means for continuously moving a wire through said auxiliary cell, and a pair of spaced contacts connecting the portion of the wire in the cell as the cathode, and the portion of the wire between contacts as an arm of the Wheatstone bridge.

17 In an automatic control for an electroplating apparatus adapted to receive an electrolyte, the combination with a plating current control means adapted to vary the plating current supplied to said apparatus, and a control circuit for said platin current control means, of a resistance bri ge means including balanced resistance arms and a means for varying the resistance of one of said arms inversely with variations of the plating ion concentration of the electrolyte to impress an electro-motive force in appropriate direction on the control circuit, operate the plating control means and increase or decrease the plating current supplied thereby.

18. In an automatic control for an electroplating apparatus adapted to receive an electrolyte, the combination with a plating current control means adapted to vary the plating current supplied to said apparatus, and a control circuit for said plating current control means, of a shunt means including a variable shunt-and a flow meter operating the same, said flow meter assuming positions corresponding to the rate of flow of electrolyte to the apparatus to impress an electromotive force on the control circuit and to vary the plating current directly with variations in the rate of flow of electrolyte.

Signed at Hollywood, California, this 22 day of Ma 1931.

K N NETH C. D. HICKMAN.