180 M. G. Lea — Gold-colored Allotropic Silver. 



reduced with milk sugar and alkaline hydroxide is left in con- 

 tact with strong hydrochloric acid even for several hours there 

 is no action, and the silver after thorough washing dissolves in 

 warm dilute nitric acid without residue. With allotropic sil- 

 ver similarly treated chloride is always formed. But strong 

 hydrochloric acid instantly converts allotropic to ordinary sil- 

 ver 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 simultaneous conversion to normal 

 silver. This double action is very curious and strongly differ- 

 entiates 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 production 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 thin gray 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 quickly converts it to normal but at the 

 same time dissolves a little of it. 



It is rather curious that the dry film of gold-colored allo- 

 tropic silver seems to be more easily acted upon by some 

 reagents than the moist precipitate. I have noticed for exam- 

 ple 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 un- 

 changed 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. 



