10 wiring and other electrical connections are eliminated from fig1 for clarity the rotating drum cathode 11 is supported on the shaft 12 received in the bearing 13 secured to the base plate 14 the shaft 12 extends upward through the plate 14 to a point of interengagement with the gearmotor 15 for slow continuing rotation of the cathode drum 11 a brush commutator assembly 16 provides electrical connection to the cathode drum 11 during the rotation of the shaft 12 the anodes 17 and 18 are also secured to the base plate 14 and cooperate with the cathode 11 to provide the electrolytic circuit in the tank the power supply unit is indicated schematically at 19 and is shown in detain in fig2 during the operation of the device silver is desposited on the cathode drum 11 and is periodically removed referring to fig2 the power source for the circuit is the center tapped transformer 19 receiving power initially through the leads 19a and 19b the output of this transformer is supplied to the pair of scr rectifiers 20 and 21 and this driving current is continuously monitored by the current sampling transformer 22 the output of which is applied across the sampling resistance 23 this produces a precise voltage feedback reference proportional to recovery current flowing between the cathode and anodes this voltage is full wave demodulated by the conventional demodulator 24 and then filtered by the standard filter arrangement 25 this output is fed to the shaping amplifier 26 whose characteristics shape the response of the cathode voltage with respect to the sensed current to modify the response to the system during the existence of a low concentration of silver ions within the solution in the tank the output.