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Silver Recovery — Hichman and Hymhnan 705
the quantity is withdrawn at each emptjing. This quantity is noted and preferably marked in ounces or cubic centimeters in bold letters on the top crock for future reference. To check the adjustment of the amount at any time subsequently it is only necessary to substitute a measuring vessel for E and turn the clip until the correct quantity (allowing thus about 50% excess) is dehvered. The apparatus is now read}^ for service.
The sodium sulphide or liver of sulphur solution is convenienth^ made in about 20% concentration. Any good quahty fused commercial sodium sulphide costing onh^ a few cents a pound may be used. It is placed in a bucket and a gallon of water added for every 2 pounds of sulphide. It should yield a black solution, red in thin layers. After an hour's settling it should decant as a clear brown fluid. It is then ready for placing in the bottles.
Performance
The somewhat complicated apparatus might be thought a mere laboratory dream finding no counterpart in practice. As a matter of fact, two units exactly as described are in use and function absolutely rehably. They hav^e reduced the labor of reclaiming hj^po to a fraction of that required pre^dously. Where waste developer is not available, the sodium sulphide solution is made up with three times its weight of caustic soda, so that both sulphiding and neutralization can take place through the side tube of the main syphon. The only added adjustment found necessary where developer is used in place of pure caustic is an occasional cleaning of the glass syphon with nitric acid to remove a deposit of silver accruing from the action of the reducing agent on the charged hypo. It is not feasible to use the desilvered h^^po over again for fixing purposes.
References
1. "The Recovery of Silver from Exhausted Fixing Baths"' by J. I. Crabtree and J. F. Ross, Amer. Ann. of Phot., 1927, p. 159.
2. "Silver Recovery^" by M. 'Ljie, Liverpool Phot. Jour., 1855, p. 87. "The Recovery of Silver from Fixing Baths" by Iv. Kriser, Kinotech
nisches Jahi'buch, 1922-3, p. 103.
"a Silver ]Mine in Every Dark Room" by G. R. Maj^er, Amer. PhotoEngraver, 1924, 11, p. 66.
3. "Syphons and Measuring De\dces'" by K. Hickman, Trans. S.M.P.E., Nov. 1926, p. 44.