M. Carey Lea — Allotropic Forms of Silver. 491 



high degree the property already described in forms A and B 

 — that of drying with the particles in optical contact. When 

 the thick pasty substance is extended over glazed paper, it dries 

 with the splendid luster of gold leaf, with this essential differ- 

 ence, that these allotropic forms of silver B and C assume 

 spontaneously in drying the high degree of brilliancy which 

 other metallic surfaces acquire by elaborate polishing and bur- 

 nishing. By brushing a thick paste of this substance evenly 

 over clean glass, beautiful gold-colored mirrors are obtained ; 

 the film seems to be entirely continuous and the mirror is very 

 perfect. 



By continued washing the precipitate changes somewhat, so 

 that in drying it takes on a coppery rather than a golden color, 

 and is rather less lustrous, though still bright and permanent. 



Two silver determinations by conversion into chloride made 

 in Nov., 1886, gave : 



No. I... 97-81 percent silver. 



No. 2 97-86 " " 



Recently these experiments have been repeated and the 

 washing was more successful. Ferric tartrate adheres very 

 obstinately and after a time washing with water ceases to 

 remove it. Stronger means cannot be employed without 

 affecting the substance itself. These last determinations gave : 



No. 1 98*750 per cent of silver. 



No. 2 98-749 " " 



The residue of No. 2 was examined and consisted almost 

 wholly of ferric citrate. 

 Chestnut Hill, Phila., April, 1889. 



Note. — The editors have received, from the author of the above 

 paper, samples of the thi*ee allotropic forms of silver which he 

 describes, and also strips of glass and paper coated with them. 

 Mr. Lea is to be congratulated on his very important results. 

 The coated strips, including the gold-colored mirror made with 

 the " gold-silver," answer fnlly to his description. The mirror is 

 remarkable for its perfection and brilliancy. 



