132 ILLINOIS STATE ACADEMY OP SCIENCE 



there were formed beautiful silver-white metallic crys- 

 tals. Much of the gray powder was rather soft and 

 malleable and when rubbed gave a metallic luster. Al- 

 ways there was a larger or smaller amount insoluble in 

 dilute nitric acid, and this appeared to be silver chloride 

 which had been affected by light. After some hours only 

 the smallest traces of silver chloride remained in the 

 solution. 



These results were so encouraging that it was felt to 

 be worth while to study the effect of various metals on 

 solutions of the halides of silver, not only in ammonia 

 solutions but in other solvents, especially in the "hypo" 

 of the photographer. It is known that large quantities 

 of the spent "hypo" liquors are discarded without the 

 recovery of the silver contained in them, thus involving 

 a great economic loss of silver as well as of "hypo". 

 While a method is in use for the recovery of the silver 

 it is felt by some photographers that it is more trouble 

 than it is worth and the use of the recovered "hypo", 

 if such it is, is not undertaken because of its possible in- 

 jurious effect on the pictures. 



"When the silver halides, silver bromide especially, is 

 dissolved in "hypo", sodium silver thiosulphate is 

 formed. The solution may contain silver ions and the 

 fact, as we show in this paper, that metals cause a de- 

 position of the silver in a very pure condition is evi- 

 dence that such is the case. 



At this point the investigation was taken up by the 

 junior author. The results, while only of a preliminary 

 nature, are interesting, and we hope to extend the scope 

 of the work at an early date. 



After most of the results, here reported, were secured, 

 there appeared in Chemical Abstracts, page 1094, (April, 

 1924) an abstract of an article in Chemische Zeitung by 

 A. Steigmann, describing "A New Method of Precipi- 

 tating Silver and Gold." In his method the solution of 

 silver halide in "hypo" is treated with sodium hypo- 

 sulphite Na 2 S 2 4 , in the presence of soda which reacts 

 with the sulphur dioxide produced during the chemical 

 action. The abstract states that the fixing bath can be 

 regenerated five or six times, but he recommends only 



