Gold-coloured Allotropic Silver, 239 



action, and the silver after thorough washing dissolves in 

 warm dilute nitric acid without residue. With allotropic 

 silver similarly treated, chloride is always formed. But 

 strong hydrochloric acid instantly converts allotropic to 

 ordinary silver, and consequently only a trace of chloride is 

 produced. By largely diluting the acid the conversion is 

 retarded and the proportion of chloride is greatly increased. 

 Thus, for example, when ordinary hydrochloric acid is diluted 

 with fifty times its volume of water and is made to act on 

 allotropic silver, about one third of the latter is converted to 

 chloride. Probably the whole would be but for the simul- 

 taneous conversion to normal silver. This double action is 

 very curious, and strongly differentiates allotropic from 

 ordinary silver. Even with the same acid diluted with a 

 hundred times its volume of water, there is a gradual but 

 complete conversion to white silver accompanied by the pro- 

 duction of a not inconsiderable quantity of silver chloride. 



Neutral chlorides also act strongly upon allotropic silver, 

 even when much diluted. So sensitive is this form of silver 

 to the action of chlorides that if in washing it on the filter 

 river-water containing a mere trace of chlorides is by an 

 oversight used instead of distilled water, a grey film of 

 normal silver will form on the surface. 



The reactions above described were obtained with the moist 

 precipitate freshly prepared. By standing for some time, even 

 if kept moist, it appears to undergo a change. When freshly 

 prepared, it is slightly soluble in acetic acid, but after standing 

 for a week or two ceases to be so. 



Sulphuric acid diluted with fifty times its volume of water 

 has no action upon normal silver. When made to act upon 

 allotropic silver, it instantly converts it to normal but at the 

 same time dissolves a little of it. 



It is rather curious that the dry film of gold-coloured 

 allotropic silver seems to be more easily acted upon by some 

 reagents than the moist precipitate. I have noticed, for 

 example, that oxalic, citric, and tartaric acids do not convert 

 the moist precipitate to normal silver, but films on pure 

 paper are gradually whitened by these acids. It is not a 

 question of strength of solution, for the moist precipitate 

 remained unchanged for twenty-four hours under the same 

 solution which whitened the same material as a dry film. 



Ammonia seems to be without converting action, but dis- 

 solves a trace. It will be shown in a future paper that there 

 exists a form of allotropic silver abundantly soluble in 

 ammonia. 



In those reactions in which allotropic silver acts the part 



