Mr. Hunt on ActinO'Chemistry. 281 



solved. The solution being of a brown colour, I am led to 

 infer that this is a suboxide of silver (7.)" 



19. A similar solution of nitrate of silver and gelatine was 

 put into a stoppered bottle and exposed to sunshine ; it speed- 

 ily darkened, and in about two hours the solution was so 

 opake that the sun could scarcely be seen through it. Its 

 colour was a grayish-green, which it retained during an ex- 

 posure to very bright sunshine for five days. It was ex- 

 pected that an increase in the acid reaction of the solution 

 might be detected during the progress of the precipitation. 

 Such can hardly be said to have been the case: the solution 

 was repeatedly tested with litmus paper, but the change of co- 

 lour was very nearly as decided at first as after the entire 

 length of the exposure. Does the nitric acid enter into com- 

 bination with the organic compound, or is it itself decomposed 

 by the combined action of the solar rays and the organic 

 matter ? 



■■ ■- 20. It was with great difficulty that the precipitated matter 

 could be separated from the solution; this was at length ef- 

 fected by subsidence, and it was found to be entirely soluble 

 in ammonia, giving a reddish-brown solution. The bottle in 

 which the solution had been placed was coated with a thin film 

 of an olive-coloured matter, transmitting green light, upon 

 which neither ammonia nor very diluted nitric acid acted. 

 By nitric acid diluted with an equal quantity of water it was 

 very speedily dissolved, the bottle becoming filled with nitrous 

 acid fumes. It is apparent from this experiment, that the first 

 action of the light is to liberate the protoxide of silver from its 

 combined acid, then to set free another proportional of oxy- 

 gen, and that eventually the suboxide is entirely reduced to 

 metallic silver. The nitric acid and the organic compound 

 are evidently thrown into some new conditions by the agency 

 of the sun's rays, the examination of which I reserve for the 

 present. 



Chloride of Silver. 



21. Perfectly pure chloride of silver was prepared by dis- 

 solving crystallized nitrate of silver in distilled water which 

 had been boiled with a little nitric acid, to ensure the absence 

 of any organic matter : it was then precipitated by pure mu- 

 riatic acid, well-washed with distilled water, separated by sub- 

 sidence, and dried on glass in a sand bath. In diffused light 

 this chloride changes colour very slowly, and eventually as- 

 sumes only a light lead colour. In bright sunshine it darkens 

 much more rapidly, and becomes brown by about one hour's 

 exposure. 



22. Under the influence of the prismatic spectrum, two very 



