22 PROCEEDINGS OP THE AMERICAN ACADEMY 



to eliminate the silica from the preparations described above by re- 

 peated ignition and fusion, and the exclusive use of platinum vessels ; 

 but it cannot be proved that the attempt was wholly successful. 

 However, the salt was at least as pure as our usual standards of 

 reference. 



Silver. — Pure silver was prepared in the first place by the re- 

 duction of pure argentic chloride by pure milk sugar, after the well 

 known method recommended by Stas. A full description of the 

 details is to be found in the account of the analysis of cupric bro- 

 mide;* indeed, some of the silver used in the present work was 

 a portion of one of the large buttons made in 1890. Oi\\y in one 

 particular was the mode of preparation modified : the silver was not 

 heated with fused potassic hydroxide. Two or three buttons of the 

 silver were fused with borax and sodic carbonate on hard-wood 

 charcoal; this treatment made no essential change in its quantita- 

 tive relations. The silver contained no oxygen, and gave very 

 qualitative and quantitative evidence of purity, t 



All of the silver which has been thus far described was fused 

 in the flame of ordinary illuminating gas. Since a strongly 

 reducing flame was used, it was presumed that no silver sulphide 

 was formed. Nevertheless, it was deemed advisable to prepare a 

 sample of the metal which should be free from even the possibility 

 of reproach. Ordinary hydrogen is apt to be quite as impure as 

 illuminating gas, hence as little adapted for the present purpose. 

 For this reason, pure hydrogen was made from pure hydrochloric 

 acid by the action of zinc which was quite free from arsenic. The 

 gas was driven through water, much potassic hydrate, through a 

 tube containing beads moistened with argentic nitrate, and finally 

 through potassic permanganate, into a gas-holder over water, where 

 it remained for some time. It was burnt in an oxyhydrogen blow- 

 pipe provided with a complete platinum tip, and served for the 

 fusion of the silver used in Experiment 19. For the support of 

 the metal during its fusion a cupel of sugar charcoal had been made 

 from pure sugar by the sole use of an alcohol lamp as the source of 

 heat. The silver itself was made from the pure silver first de- 

 scribed by dissolving it in nitric acid and electrolytically depos- 

 iting it with the aid of two Bunsen cells, J two plates of the same 



* These Proceedings, XXV. 197, 198. 



t Ibid. ; also this paper, pages 17, 28, 29. 



t J. L. Hoskyns Abrahall, Journ. Ch. Soc. Proa, 1892, p. 6G0. 



