PAPERS OX CHEMISTRY AND P] 



three tin: ■-. Since the hyposulphite is usually ma. 



n of the sulphite with zinc, and - must 



be us neutralize the sulphur le which is eon- 



verted into sulphite and this in acid solution, in which 

 the "hypo** i- ah - sulphur di 



which m - * in an injurious way upon the pictu: 



seems a more direct and better method to use the zinc 

 directly with the "hypo" in reco" the silver. This 



would be especially true ii roni our 



'he hyp - ife a fi:: _ 



:ment with the zinc as when freshly ma 

 In in a more nearly way 



action of several n r er chlo- 



in ammonia, a nearly saturat :he chlo- 



- made and one-half of it was diluted with an 

 I volume of distilled water. In separate port 

 th the concentrated and dilute solutions were pi 

 :Iied amounts of the metals, zinc, aluminum, 

 and iron and th kept in a dark room until 



all the silver had been precipitat :ore the metals 



iced their surfaces were w cned. 



all the metals except iron preeipitatk : n at 



once and all the silver had left the - o within twenty- 



four hours (the fir- was made at the end of this 



time). In the case of iron in the dilute solution the 



n had started only slightly at the end of the 

 hour and was complete only after for : hours. 



In the concentrated solution the iron remained perfectly 

 bright for the first day. and n 



posited. On being brought into the light, however, ac- 

 tion began within fifteen minutes and - to con- 

 tinue after it had been replaced in a dark room. "When 

 the action had become complete the metals were re- 

 moved, cleaned and wei a and the precipitate treated 

 with quite dilute nitric acid. In the a zinc quite a 



, amount of material 1 - Lved in the 



and appeared like darkened silver chloride. With the 

 other metals only a trace of material w to be 



insoluble. In the t zinc it was found that 



more went into solution than was equivalent to the silver 

 _:it be anticipated from the fact that 



