Mr. Hunt on ActinO'Chemistryf 283 



some free nitrate of silver in mixture with it. It was import- 

 ant to ascertain, if possible, the cause of this. Three pieces 

 of glass covered with films ofchloride of silver, by subsidence, 

 in the manner recommended by Sir John Herschel, were se- 

 lected; one was exposed quite dry, another moistened with 

 distilled water, and the third with a solution of nitrate of silver. 

 The action was most rapid on that wetted with the nitrated 

 solution, the next in order was the moist one. In an hour 

 they were however darkened to as nearly as possible the same 

 shade of colour. 



"f^25. The glass plate over which the wash of nitrate of silver* 

 had been applied, was soaked in distilled water to remove any 

 of that salt that might remain undecomposed. The three 

 pieces of glass with their darkened films were then boiled se- 

 parately in nitric acid diluted with double its quantity of water. 

 The colours of the plates were but very slightly changed. 

 The liquids were then examined for silver, and in that alone 

 in which the plate on which the nitrate had been spread had 

 been, was any detected. It was evident that the nitric acid 

 had either dissolved off oxide of silver, or oxidized metallic 

 silver and then dissolved it. The films on the other plates 

 were not changed in colour by the applicaXion of either ara- 

 rfi'onia or hyposulphite of soda. ■ uioif i i)ojii '(/qn n ?.A .frii? 



^6. Three similar plates of glass covered with films of chloi- 

 ride of silver wei'e placed in jars of pure hydrogen and nitro- 

 gen gases and in atmospheric air, and then exposed to bright 

 diffused daylight. The object of this was to ascertain if the 

 nitrogen of the acid, or the hydrogen of the water, were likely 

 to assist the change in any way. The chloride in the nitro- 

 gen and the atmospheric air darkened equally in equal times. 

 The first action of the hydrogen on the chloride of silver was 

 to reduce it to the state of metal over the surface. But as soon 

 as the chloride began to darken, this bright metallic film was 

 removed, and the whole darkened equally, but to a deeper 

 tint than either of the others. These plates, as in the former 

 case, were boiled in diluted acid, from which experiment I as- 

 certained that the hydrogen plate alone gave any evidence of 

 the presence of oxide of silver or revived metal. ix 



27. It may appear that this metal was produced by the hy*. 

 drogen independent of the actinic power, but I find when 

 chloride of silver is plunged into hydrogen gas in bright sun- 

 shine, that no reduction of the chloride due directly to the 

 hydrogen takes place, yet most distinct evidence of the pre- 

 sence of metallic silver after darkening has been obtained. 

 We thus learn that the advantage of the nitrate of silver over 



the chlorideis, that it is more readily reduced to tjie metallic 

 ..tdi Liife t-i-oi ^ti'eii ^hti tOtdi idi snisBgsM ijs3iriqoeolirt4 ^ 



