Mr. Hunt on Actino-Chemistry, 277 



•3j9IB0f0f| J-. TO i>iL ., .-., 



Oxides of Stiver. 



3. To a weak solution of nitrate of silver in distilled water 

 a very dilute solution of pure baryta was added, and the re- 

 sulting precipitated oxide of silver received upon plates of 

 glass. When the whole of the oxide had fallen down, the 

 fluid was removed very slowly by means of a small glass si- 

 phon, so that the powder on the glass plates might not be dis- 

 turbed. Without being removed from the vessel in which 

 the precipitation was effected, the oxide was dried at a very 

 moderate heat, and there resulted exceedingly thin films of 

 the oxide of silver on the glass, quite free from all organic 

 matter, every precaution being taken to prevent its presence. 



4. These plates were exposed to full sunshine for periods 

 varying from one to twenty-four hours, one-half of them being 

 covered with an opake body. The brown oxide of silver 

 (protoxide) was gradually darkened, so that after half an 

 hour's exposure, the exposed part was a much deeper brown 

 than that which had been covered. This darkening process 

 was continued until a perfect black was produced, after which, 

 by the prolonged action of sunshine, a very remarkable 

 whitening of the oxide takes place, and proceeds slowly until 

 it is of a very fine olive colour. uinn'ursv 



5. On immersing one of these plates in Strong ammonia, all 

 the oxide which had been kept from the solar action was dis- 

 solved off, whereas the exposed part did not appear to be 

 acted on. Another plate, immersed in a solution of twenty 

 drops of nitric acid in 300 drops of water, was acted on in pre- 

 cisely the same manner; the oxide being entirely removed from 

 the unexposed portion of the glass plate, whilst the changed, 

 or actinized part, appeared to remain untouched. From this 

 we might consequently infer that the oxide of silver had been 

 leduced to the metallic state. Moderately strong nitric acid, 

 dissolving the whole from the glass, seemed to render this in 

 every way probable. 



6. Metallic silver, in however fine a state of division it may 

 be, conducts electricity; consequently it was expected that 

 the changed oxide would conduct the current of a voltaic bat- 

 tery. One of the glass plates covered with oxide was made 

 part of the circuit, between a single pair and a galvanometer 

 of great delicacy, but not the slightest indication of any con- 

 ducting power could be detected. 



7. Films of oxide of silver were darkened all over by long 

 exposure to sunshine. One was placed in ammonia and an- 

 other in very dilute nitric acid. It was now discovered that 

 the ammonia did dissolve a portion of the actinized oxide ; it 



