US3926768A

US3926768A - Silver recovery system

Info

Publication number: US3926768A
Application number: US350464A
Authority: US
Inventors: Kenneth G Burgess
Original assignee: Hydrospace Industries Inc
Current assignee: Hydrospace Industries Inc
Priority date: 1973-04-12
Filing date: 1973-04-12
Publication date: 1975-12-16
Anticipated expiration: 1992-12-16

Abstract

Silver is recovered from spent photographic solutions by feeding the spent solutions into a pre-collecting vessel where the solution collects until a predetermined volume has been received, at which time it is automatically dispensed, by a self-triggering syphon, into an electroylsis chamber, and direct current is automatically turned on for a predetermined period of time between an anode and a cathode in the chamber to plate out the silver onto the cathode. A magnetic agitator is automatically energized to keep the silver suspended.

Description

United States Patent 11 1 1111 Burgess Dec. 16, 1975 [54] SILVER RECOVERY SYSTEM 3,715,291 2/1973 Bentley 204/275 X [75] Inventor: Kenneth G. Burgess, Derby, N.Y.

Primary Examiner-John H. Mack [73] Ass1gnee: Hydrospace Industr1es,lnc., Buffalo, Assistant w 1 Solomon Attorney, Agent; or FirmRaymond F. Kramer [22] Filed: Apr. 12, 1973 21 Appl. No.2 350,464 [571 ABSTRACT Silver is recovered from spent photographic solutions [52] U5. CL 204/229, 204/109, 204/273, by feeding the spent solutions into a pre-collecting 204/275, 204/294 vessel where the solution collects until a predeter- 51 Int. cm czsc 7/00 mined mlume has been received which time is 58 Field of Search 204/109 229 261 273 automatically dispensed by a self'triggering P 2 I275 into an electroylsis chamber, and direct current 1s automatically turned on for a predetermined period of [56] References Cited time between an anode and a cathode in the chamber to plate out the silver onto the cathode. A magnetic 2 563 903 S Z STATES PATENTS agitator is automatically energized to keep the silver l l Zadra 204/275 X sus ended 3,477,926 ll/l969 Snow et al. 204/109 p 3,694,341 9/1972 Luck, Jr 204/273 18 Claims, 7 Drawing Figures US. Patent Dec. 16, 1975 Sheet2of3 3,926,768

FIG. 5

FIG. 6

llf/f/l/ US. Patent Dec. 16, 1975 Sheet 3 of3 3,926,768

INPUT BINARY T l I I I I I U P DOW N COUNTER us TIMER "0 V. AC.

FIG. 7

SILVER RECOVERY SYSTEM BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to silver recovery from spent photographic solutions, and in particular to an automatic, operator-less, system particularly useful for recovering silver from spent X-ray developing solutions ules. The intensity of the light will determine the number of metallic silver atoms formed. Granules of the silver bromide containing metallic silver are sensitized, and can be reduced to metallic silver by an organic agent known as developer. The developer reduces the exposed granules more easily than the unexposed granules, and by chemically controlling the developer action, the non-sensitized regions of the film remain unchanged. The film now passes through a second chemical, known as fixer, where a second and very unique action occurs. The unsensitized areas are, of course, still made up of silver bromide and/or chloride, which is able to react with the chemical fixer, causing a washing of the silver from these unsensitized areas of the film. The number of silver granules washed away is dependent upon the density of the unsensitized granules in any' one region of the film. In photographic studios, motion picture labs, industrial X-ray centers and hospitals, this silver is passed out of the processor into a number of differing types of silver recovery systems, or directly into the drain.

To date, the most popular system of silver recovery in institutions such as hospitals has been the canister method. The system is very ineffective for a number of reasons. The canister is nothing more than a bucket, ranging in capacity from 5 to 50 gallons, containing iron wool with a number of passages through it, depending upon the manufacturers design. As the silverladen solution passes through the iron wool, the iron ions replace the silver ions in solution, and metallic silver in the form of sludge appears within the iron mesh. The silver is combined with'a number of other chemicals and chemical compounds, iron and iron sulfide, as an example, and a multi-stage refining operation is required before any acceptable level of silver purity is attained. The cost of the system is relatively small, varying, depending on size, between $16.00 and $200.00, but it can never be re-used. Additionally, the canister method has a limited life, because only a certain number of gallons of solution can pass through it before all of the removal property is gone. The canister also decreases in efficiency with age, due to internal oxidation and a number of physical reactions undergone as the solution deposits silver in the iron mesh. Typical efficiency averages about 30-70% of the total recoverable silver passed into the canister in solution. Typical life expectancy for such a unit in a hospital would be 1 month.

A second system for removing silver from solution is called zincing. The system consists of salting or doping large quantities of spent hypo solution with zinc flakes. The solution is then drained off, leaving large quantities of precipitated silver sludge, which must, in turn, be refined. The operation of this system requires that the participating institutions store solutions and sell them to a zincing operation at a fraction of the solutions silver worth. In addition, the system is laborious and space-consuming, requiring large users of hypo solution to maintain considerable storage facilities in usually critically needed space. The system is a source of marginal revenue in most cases, considering the worth of the silver contained in such solutions.

The third system available to remove silver from hypo solutions iselectrolysis, or electroplating. This system has the capability of being the most efficient of all processes, due to the fact that the silver is reclaimed in nearly pure form (92-98%). The basic system has several disadvantages. It involves largecapitol outlay. and only when comparatively maintenance-free can the unit demonstrate superiority. The prior art machinery normally marketed does not contain an automated control apparatus due to cost, and requires considerable attention. If the'machine is left unattended, it will continue at a given current level regardless of fluidflow or solution density, and will decrease in efficiency by losing silver, or begin to cause sulfidization, gas emission and destruction of the purity of the silver already plated. Operation at current levels too high for need place undue strain on all parts of the machinery and resulting gases emitted can cause considerable discomfort in the area in which the machinery is located. Such phenomenon, production of hydrogen sulfide, causes a noxious rotten egg smell.

Machines have been marketed with a number of control mechanisms, including impedance control. All require secondary adjustment and are considerably more expensive due to this additional equipment. Prior art machinery employs, for agitation, rotation of the cathode or rotation of the anode. Such systems require motorization large enough to carry the final full laden weight of the respective element and in addition require direct mechanical connections to be made in a difficult atmosphere. The cathode rotation system also requires that rotation be maintained at a significant speed, most commonly rpm, which may, due to centrifugal forces involved, cause premature flaking from the cathode and may retard plating efficiency in low silver density concentrations.

It is a primary object of the present invention to provide an improved silver recovery unit that is not subject to the above-mentioned disadvantages of the prior art and that, in particular, has stationary and easily removable cathode and anode.

It is another object of the present invention to provide an improved silver recovery system which operates automatically, without the necessity for an operator, which does not produce any noxious gases therefrom and which is easily serviced for checking and removing the amount of silver plated out.

SUMMARY OF THE INVENTION A method and apparatus for recovering silver from spent photographic solutions (particularly spent photographic solutions from X-ray development in hospitals) is provided wherein the spent solutions are fed, as they are generated, into a pre-collecting vessel of the silver recovery unit. The pre-collecting vessel holds the spent photographic solution until a predetermined volume is collected, at which time it is automatically dispensed into an electrolysis chamber and a current is automatically passed between a cathode and an anode in the electrolysis chamber for a predetermined period of time to plate out the silver on the cathode. The silver is kept suspended (during the time that the current is on) by a magnetic agitator located in the bottom of the electrolysis chamber. A discharge opening is located at the top of the electrolysis chamber to maintain the chamber full, up to a predetermined level. The cathode may be graphite of a parabolic shape in vertical section to provide good silver suspension and to minimize frothing. A hinged cover is located over the electrolysis chamber for easy viewing of the chamber. The cathode and the anode are both easily removed by simply pulling them upwardly out of the chamber. The pre-collecting vessel includes a floating magnet and a pair of vertically spaced-apart magnetic reed switches properly located in relation to a self-triggering syphon that automatically dispenses a predetermined volume of the solution into the electrolysis chamber.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be more fully understood by reference to the following detailed description thereof, when read in conjunction with the attached drawings, wherein like reference numerals refer to like elements, and wherein:

FIG. 1 is a cutaway partly cross-sectional elevation view of the apparatus of the present invention;

FIG. 2 is a cross-sectional elevational view of the apparatus shown in FIG. 1 along lines 22 of FIG. 1;

FIG. 3 is a plan view looking down into the apparatus of FIGS. 1 and 2;

, FIG. 4 is a cross-sectional view of the pre-collecting vessel of the present invention;

FIG. 5 is a horizontal cross-sectional view of the pre-collecting vessel;

FIG. 6 is a plan view of the magnets used in the magnetic agitator; and

FIG. 7 is a schematic block diagram of an electric circuit used in the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT With reference now to the drawing, a brief overall description of the apparatus will first be provided. followed by a detailed description of each element thereof. FIGS. l-3 show a silver recovery unit l0made according to the present invention and including a base 12 and a cover 14 hinged at 16 to the base. Spent photographic solution is fed into the unit through an inlet tube 18 in the top of the cover 14 by means of a coupling (not shown) on the end of the tube 18. The tube 18 feeds the solution into a pre-collecting vessel 20 where it remains until a predetermined volume (such as 800 ml) has built up, at which time the solution is automatically dispensed into an electrolysis vessel 22 having a chamber 24. After the solution is dumped into the chamber 24, current is automatically turned on, for a predetermined time period. between an anode 26 and a cathode 28 to plate out the silver on the cathode 28. The chamber 24 is kept full up to a level determined by a discharge tube 30. During the time the current is on, a magnetic impeller 32 in the bottom of the vessel 22 is energized to keep the solu- 4 tion agitated to keep silver from falling by gravity in the bottom of the chamber 24.

Referring now in detail to the various elements of the unit 10, the base 12 includes a housing 34 having a support 36 for supporting the electrolysis vessel 22 therein. The housing 34, electrolysis vessel 22, and the cover 14 are preferably made of fiberglass, such as 197A, Hetron fiberglass, which is impervious to mild acids and gases. The unit 10 has a wrinkle finish rendered in black to be non-reflective for specific use in the darkroom. The electrolysis vessel 22 has no opening in its lower end, the only discharge opening being discharge tube 30. The electrolysis-vessel 22 does have a central, vertical, support tube 38 which supports the cathode 28. The bottom wall 40 of the electrolysis vessel 22 includes a recess '42 with a pair of bearing rings 44, preferably of Teflon, in the bottom thereof.

The impeller 32 is rotatably mounted about the support tube 38 in the recess 42. The cathode 28 has a central axial opening 46 therein having a depth such that a bottom end 48 of the cathode 28 is spaced above (approximately three-fourths inch) the impeller 32.

The cathode 28 is preferably of HC type solid graphite, about 6 inches in diameter at the top, and has a parabolic shape (hereby defined to include a truncated parabolic shape and similar curved shapes) in vertical section, as shown in FIG. 2, with the apex adjacent the bottom of the electrolysis chamber 24. The cathode 28 has a handle 50, preferably ofstainless steel, to aid in pulling the cathode up out of the chamber 24, as when it is time to remove the silver that has plated out on the cathode. The electrical connection 52 is attached to one of the screws used to connect the handle 50 to the cathode. The parabolic shape of the cathode provides a good homogeneous mixture with good suspension of the silver while minimizing frothing. The cathode 28 is a parabolic shaped configuration made of HC type graphite for good conductivity, low cost, durability, and unexpected minimization of sulfiding. In one example. after most of the silver had been plated the same high current was left on, producing, with other than the graphite cathode of the present invention, much hydrogen sulfide gas, and unexpectedly, very little hydrogen sulfide gas was produced when the cathode was a graphite cathode. The parabolic bottomis constructed to induce constant flow patterns without unnecessary turbulence. It is important that the solution be continually mixed as silver ions near the cathodes are removed toinsure a homogenous mixture without foaming. The cathode material has been determined to be instrumental in plating efficiency, especially in a start-up situation. For this purpose a graphite cathode was found to be the most acceptable. With this material the formation of hydrogen sulfide gas (H S) is greatly reduced and sulfiding is reduced by an extreme factor. It was found that a graphite electrode allowed overage in current by from calculation with very little sulfiding and production of H S gas.

The anode 26 is preferably a flat stainless steel sheet folded into a cylindrical shape and inserted into the chamber 24 and allowed to ,unwind up against the sidewall of the chamber 24. An electrical connector 54 is provided at the top of the anode 26. A slot 56 is provided in the anode 26 in alignment with the discharge tube 30. The anode 26 can be removed from the chamber 24 by simply lifting up the cover 14, disconnecting an electrical lead 58, and pulling the anode directly up out of the chamber 24. To aid in removal,

the anode 26 can be formed into a smaller cylinder before removal. Stainless 316 anodes are a special addition to the plating field themselves, becasue of their extremely long life expectancy in hypo solutions. There is an initial inherent problem in plating with stainless, and for this reason the anode 26 is preplated with silver. Without preplating, primary plating on a clean cathode would require high density silver laden solution to achieve desired plating efficiency.

To keep the silver in suspension, the unit has an agitator 60 including a motor 62 mounted under the bottom wall 40 of the electrolysis vessel 22. The motor is connected to a cooling fan 63 and to an inducing magnet 64 located just below the impeller 32. The impeller 32 includes a magnet 66 and vanes 68, preferably made of Plexiglas, and connected to the top of the magnet 66 as by epoxy glue. The inducing magnet 64 and the impeller magnet 66 each are made as shown in FIG. 6. FIG. 6 shows a ceramic ring (for example of barium carbonate and iron oxide) that is magnetized on one surface only thereof in the manner shown in FIG. 6. In the inducing magnet 64 the top surface is magnetized and in the impeller magnet the lower surface is magnetized. By this magnet, greater efficiency is achieved by utilization of a circular field concentric to the rotational movement of the magnet. The magnet 64 maintains a constant distance-torque parameter. The distance between the adjacent segments is a constant, while in prior art magnetic agitation magnets using bar magnets, the distance between adjacent ends is greater at the outside than at the inside, i.e., the gap tapers outwardly in width rather than being of constant width.

The agitation system of the present invention gives maximum agitation without breaking the surface of the liquid and causing foaming. The agitator is also designed to induce maximum mixing with the least amount of rotation. This system is significantly superior to the standard rotating cylindrical cathode design which, due to its dynamic properties, causes cylindrical rotation with little true mixing of the solution. To achieve maximum mixing, the interior mixing magnet 66 has vanes 68 of unequal height, but with equal area, causing strong turbulence radiation from the impeller The pre-collecting vessel is preferably made of plexiglass and is mounted under the cover 14. The pre-collecting vessel 20 includes a self-triggering syphon 70 for automatically dispensing solution from the pre-collecting vessel to the electrolysis chamber 24 after a predetermined volume of solution has collected in the pre-collecting vessel. The pre-collecting vessel 20 also includes a reed switch package 72 for sensing when the solution is fed to the electrolysis chamber 24 and for feeding the released volume information to an up-down counter l 14 (see FIG. 7) that switches on the current to the

electrodes

26 and 28 for a predetermined period of time, and for energizing the agitator 60.

Referring now to FIGS. 4 and 5, the syphon 70 includes an inverted tube 74 having an opening 76 spaced from a bottom wall 78 of the pre-collecting vessel 20 and supported by an arm 80. Positioned inside of the tube 74 is a smaller tube 82 extending down through the bottom wall 78 in fluid tight relationship therewith. The top of the smaller tube 82 is connected to the larger tube 74; however, the smaller tube 82 has a serrated (or scalloped) edge 84 to allow fluid to pass from inside of the tube 74 to inside of the tube 82. The

6 syphon also includes a tube 85 slidably fitted inside of tube 82. The tube 85 can be slid up beyond the bottom of the serrated edge 84 to vary the size of the openings through the serrations to set the syphon start point for variations in surface tension.

In operation, solution feeds into the pre-collecting vessel 20 through the inlet tube 18, and collects in the vessel 20 until the level rises above the serrated edge 84 at which time a syphon action takes place and the solution feeds out of the vessel 20 through the tube 82, until the level in the vessel 20 reaches the level of the opening 76. The pre-collecting vessel thus automatically collects solution and automatically dispenses a predetermined volume thereof (for example, 800 ml.) into the electrolysis chamber 24. Any volume can be dispensed, as long as the circuitry is designed (or adjusted) with this amount of solution and consequently with this amount of silver, in mind.

The inlet tube 18 of the cover mounted pre-collecting vessel 20 is positioned to allow the cover to be hinged open with no spillage or loss of solution.

The reed switch package 72 comprises a tube 86 (sealed from any liquid in the vessel 22) in which are positioned upper and lower magnetic reed switches 88 and 90. A float 92 with a central axial bore is located about the tube 86 and includes a pair of magnets 94, for actuating the

switches

88 and 90. The reed switching unit 72 is a dual unit, having one activator at the bottom of the float stroke and one 88 at the top to ensure that liquid bounce will not activate it. After the top position is met, the syphon 70 reaches its critical measuring point and dispenses solution. However, the

switches

88 and 90 do not initiate the current until the fluid level drops and the lower switch 90 is activated in sequence after the upper switch 88 has been activated.

The unit 10 also includes a fliter and a full wave rectifier 96 below the electrolysis vessel 20. A front compartment 98 is connected to the housing 34 by hinges 100 and includes an ammeter 102, an on-off switch 104, and a red light 106 to indicate when the unit is on. Wiring to the

electrodes

26 and 28 extends through this compartment 98.

FIG. 7 shows, schematically, an electrical circuit used in the present invention; it will be readily understood by one skilled in the art. The circuit includes the reed switch package 72, including the float 92 and the reed switches 88 and 90, the agitator motor 62, and the cathode 28 and anode 26. The pre-collecting vessel 20 receives hypo and stores it until the self-triggering syphon 70 is tripped. Just before the syphon 70 is tripped, the magnetic float 92 which follows the level of the hypo, causes the upper switch 88 to close and this pulse satifies one-half of the required function to turn the system on. After the liquid is dumped and the level reaches its lowest point, the float 92 causes the lower switch 90 to close completing the requirements to store one bit of information (the switches must close in that order). The storage of a bit sets the unit in operation. by an electronic switch 112 controlled by an up-down counter l 14, and continues the electrolysis for a preset time by means of a timer 116, for each bit received.

The unit 10 is designed for the reclamation of silver from photographic (hypo) solutions, removes from to 99% of all contained silver, and does so at purity levels of 92% or better in both high and low density solutions.

The unit is self contained, powered by either 1 lOVAC or 22OVAC, or with the addition of a portable power pack, nearly any DC voltage above 6v. The unit in full operation uses approximately 75 to 80 watts. Under normal conditions, the unit will use an average f watts, or approximately 0.72 Kw-hrsper 24 hour period. The wattage drawn depends upon pre-set current densities in the machine itself. Due to a number of unique features, this machine can efficiently cope with a wide variety of work loads. including sporadic major and minor loads. The machine is an on-site system, connected directly to X-ray or photographic processing equipment.

As'will be seen from the above description, the present invention provides a silver recovery unit that: (l) employs completely enclosed electrical and mechanical components, (2) employs a fiberglass casing that is impervious to mild acids and gases and which maintains a good appearance and durability, (3) includes individually removable anode and cathode for maintenance, cleaning and silver removal, (4) employs magnetic agitation to insure maximum isolation of motors and mechanical drive systems from corrosive gases and liquids and to insure non-leakage in the drive system, (5 employs a parabolic tipped cathode to insure maximum good'mixing while reducing foaming, (6) employs a stainless steel anode which can be plated with silver when necessary for maximum plating efficiency during start-up even in light density solutions, (7) employs a pre-collecting vessel with a self-triggering syphon start and a break point system coupled electromechanically for automatically dispensing a predetermined volume of solution into the electrolysis chamber, and for turning on the current to the electrodes at a predetermined time period respectively, (8) provides a hinged cover to allow quick and easy check of the silver collection without having to remove either the cathode or the anode, and (9) employs a graphite cathode having the properties described above.

The invention has been described in detail with particular reference to the preferred embodiment thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims. For example, other types of precollecting vessels can be used other dispensers than the syphon 70 can be used and other switch means can be used in place of thefloat and magnetic reed switch 72. Other types of agitation can be used to maintain the silver suspended. For purposes of the present specification and claims, the term loosely as applied to the

electrodes

26 and 28, is defined to mean unconnected byany structural element, that is, the

loose electrodes

26 and 28 can be lifted directly out of the vessel 22 without first having to disconnect them from any structure (the electrical leads are not a structural element").

I claim:

1. An apparatus for recovering silver from spent photographic solutions comprising:

a. an electrolysis vessel having an electrolysis chamber therein;

b. an electrode removably positioned in said vessel adjacent a wall thereof;

c. an electrode of opposite sign positioned at or near the center of said vessel; I

d. an impeller located within said vessel adjacent to or near the bottom thereof;

6. means for rotating said impeller:

f. a pre-collecting vessel positioned above the electrolysis chamber and including means for receiving spent photographic solution to be fed into said chamber and siphon means for dispensing a predetermined volume of said solution into said chamber; and 1 g. means for-passing an electric current between said electrodes and through the solution in said electrolysis chamber for a predetermined period of time in response to the dispensing of said volume of solution from the pre-collecting vessel into the chamber.

2. An apparatus according to claim 1 wherein the centrally positioned electrode is graphite.

3. An apparatus according to claim 1 wherein the centrally positioned electrode is of a parabolic shape in vertical cross-section with its apex adjacent the impeller. I

4. An apparatus according to claim 1 wherein the rotating means comprises means for magnetically rotating the impeller.

5. An apparatus according to claim 1 wherein the electrolysis vessel includes an exit opening in a side wall thereof adjacent the top thereof.

6. An aparatus according to claim 1 wherein the impeller includes a plurality of vertical vanes of equal centrally positioned electrode has an opening in its lower end.

10. An apparatus according to claim 9 wherein the centrally positioned electrode has a parabolic shape in vertical cross-section with its apex adjacent the impeller.

11. An apparatus according to claim 10 wherein the impeller is circular and the rotating means comprises means for magnetically rotating the impeller.

12. An apparatus according to claim 11 wherein the centrally positioned electrode is the cathode.

13. An apparatus according to claim 1 wherein the pre-collecting vessel includes a self-triggering siphon for dispensing photographic solution into said electrolysis chamber after a predetermined volume of solution collects in said-collecting vessel.

14. An apparatus according to claim 13 wherein the means for passing an electric current between the electrodes and through the solution in the electrolysis chamber for a predetermined period of time in response to the dispensing of a volume of solution from the pre-collecting vessel into said chamber includes switch means in said pre-collecting vessel.

15. An apparatus according to claim 14 wherein said switch means includes a pair of vertically spaced-apart magnetic reed switches.

16. An apparatus according to claim 15 wherein the electrode removably positioned in the electrolysis vessel and adjacent a wall thereof is essentially cylindrical and is positioned adjacent the inner side wall of the 10 them so that photographic solution can rise in the annulus between the tubes as it rises in the pre-collecting vessel, said cylinders being closed across the tops thereof and having a passageway between them at the tops thereof to permit siphoning flow of solution from the pre-collecting vessel body of solution, through the annulus, the passageway and the internal tube to the electrolysis chamber.

Claims

1. AN APPARATUS FOR RECOVERING SILVER FROM SPENT PHOTOGRAPHIC SOLUTIONS COMPRISING: A. AN ELECTROLYSIS VESSEL HAVING AN ELECTROLYSIS CHAMBER THEREIN; B. AN ELECTRODE REMOVABLY POSITIONED IN SAID VESSEL ADJACENT A WALL THEREOF; C. AN ELECTRODE OF OPPOSITE SIGN POSITIONED AT OR NEAR THE CENTER OF SAID VESSEL; D. AN IMPELLER LOCATED WITHIN SAID VESSEL ADJACENT TO OR NEAR THE BOTTOM THEREOF; E. MEANS FOR ROTATING SAID IMPELLER; F. A PRE-COLLECTING VESSEL POSITIONED ABOVE THE ELECTROLYSIS CHAMBER AND INCLUDING MEANS FOR RECEIVING SPENT PHOTOGRAPHIC SOLUTION TO BE FED INTO SAID CHAMBER AND SIPHON MEANS FOR DISPENSING A PREDETERMINED VOLUME OF SAID SOLUTION INTO SAID CHAMBER; AND G. MEANS FOR PASSING AN ELECTRIC CURRENT BETWEEN SAID ELECTRODES AND THROUGH THE SOLUTION IN SAID ELECTROLYSIS CHAMBER FOR A PREDETERMINED PERIOD OF TIME IN RESPONSE TO THE DISPENSING OF SAID VOLUME OF SOLUTION FROM THE PRE-COLLECTING VESSEL INTO THE CHAMBER.

3. An apparatus according to claim 1 wherein the centrally positioned electrode is of a parabolic shape in vertical cross-section with its apex adjacent the impeller.

6. An aparatus according to claim 1 wherein the impeller includes a plurality of vertical vanes of equal areas and different shapes.

7. An apparatus according to claim 1 wherein the removably positioned electrode is a flat stainless steel sheet bent into cylindrical form and inserted into said chamber, which is readily removable therefrom.

8. An aparatus according to claim 7 wherein the removably positioned electrode includes an electrical connection at a top portion thereof and includes an opening in a side wall thereof mating with an exit opening in the electrolysis vessel.

9. An apparatus according to claim 1 wherein the centrally positioned electrode has an opening in its lower end.

16. An apparatus according to claim 15 wherein the electrode removably positioned in the electrolysis vessel and adjacent a wall thereof is essentially cylindrical and is positioned adjacent the inner side wall of the electrolysis chamber so that it can be removed directly upwardly from said chamber.

17. An apparatus according to claim 16 wherein the electrode is a flat stainless steel sheet bent into a cylinder and inserted in said chamber and can be removed by bending it into a smaller cylinder and pulling it directly upwardly out of said chamber.

18. An apparatus according to claim 13 wherein the self-triggering siphon includes external and internal vertical tubes with an annular passageway between them so that photographic solution can rise in the annulus between the tubes as it rises in the pre-collecting vessel, said cylinders being closed across the tops thereof and having a passageway between them at the tops thereof to permit siphoning flow of solution from the pre-collecting vessel body of solution, through the annulus, the passageway and the internal tube to the electrolysis chamber.