| 摘要 |
<p>381,903. Electrolytic recovery of silver from photographic fixing baths. KODAK, Ltd., Kingsway, London.- (Assignees of Hickman, K. C. D. ; Kodak Park, Rochester, New York, U.S.A.) June 4, 1932, No. 15874. Convention date, June 4, 1931. [Class 41.] A photographic fixing solution is continuously circulated between the fixing baths and electrolytic cells in which the silver content is reduced from say 2-3 gms. per litre to 0.5-1 gm. per litre. In addition a small portion of the solution is withdrawn to other cells in which substantially the whole of the silver is removed, this portion after electrolysis being preferably discharged to waste. Two of a set of cells 33 are shown in the drawing. Filtered solution from the fixing baths is supplied through regulating valves 35 and withdrawn by pipes 46, in one of which a two-way cock 50 is provided for discharge to waste. The circulating solution is led to a tank 48 provided with means for automatic regulation of the amount of liquid in circulation and of its concentration before return by a pump 66 to a storage tank for passage through the fixing bath. Fixing solution of normal strength is supplied by a pipe 55 controlled by a float-valve 58 or a hand-valve 56. Strong sodium thiosulphate solution is supplied by a pipe 62 in amount regulated in the following way. The pipe 67 from the pump 66 is provided with a byepass 69 having a tap 74 discharging into a funnel 72 at the top of a U-tube 71 the other limb of which ends in an adjustable spout 75 above the tank 48. A central vertical pipe leads to chamber 77 fed with water by a pipe 78. The strength of the solution in the U-tube controls the water level in the chamber 77 which acts through a float 80 and levers to regulate the closure of a length of rubber hose 63 in the pipe 62. A solution of hardening substance may be supplied by a pipe 52. Each electrolytic cell is provided with an agitator driven by a pulley 36. A suitable fixing bath comprises 300 parts sodium thiosulphate, 10 parts sodium sulphite, 10 parts acetic acid or the equivalent, 10 parts chrome alum, and 1000 parts water.</p> |
