It is economically and ecologically desireable to recover metallic elements from solution baths, such as photographic and radiographic fixing solutions.  An example of a device for accomplishing such recovery is described in U.S. Pat.  No.  3,694,341, issued Sept. 26, 1972.  It consists generally of a container whose outer wall is a cylindrical cathode and which has an anode suspended centrally thereof.  Electrical current is passed between the anode and cathode through the fixing solution causing silver or other metallic material in solution in the fluid to be deposited on the cathode by electrolysis. 
While the electric current passing through the fluid produces an electrolytic deposition of metal on the cathode, it can also cause a ruinous change in the chemistry of the solution, depending on the amperage and time of current flow.  For this reason, it is important to control the electric current so as not to damage fixing solutions with resultant destruction of film.  In most applications of metallic recovery devices, proper control has not been available primarily because the solutions being treated are grossly variable in their amount of metallic content over a given period of time.  In the prior art, in order to insure protection of the solution from a damaging chemical change, a "low profile" current regime was used where a constant low current was applied based on average free silver production per time period or film increment.  Since the efficiency of the electrolysis is a function of higher currents, it is apparent that conservative current levels established for protection of the chemistry of the fixing solution results in low metallic recovery efficiency. 
It is the primary object of the present invention to provide a control system for the application of current to a metallic recovery device to control the current level as a function of metallic content of the solution and hence increase the efficiency of metal recovery. 
Another object of the invention is to provide a control system such as the one described which will protect the solution from damagingg chemical change.