34: THE ANALYSIS OF POTA55IC BROMIDE. 



surrounded it in the tube, so that no certain quantitative evidence could 

 be obtained. Two minute black spots were visible in the boat; nothing 

 else could be seen upon very careful scrutiny. If there were any silica 

 present, the amount must have been too small to have had any appreciable 

 influence on the final atomic weights. Time and material were lacking, 

 hence the experiment was not repeated. 



SILVER. 



The essential details of the preparation of pure silver, as developed by 

 Richards and Wells, were followed in detail, and the reader is referred 

 to their paper, as well as to the preceding paper of Richards and Staehler. 

 for the particulars. Two samples of silver were made ; they were found 

 to be identical in quantitative behavior. 



The source of the material used for the first preparation was the pure 

 precipitated argentic chloride remaining from the work of Richards and 

 \Yells on sodium. It was reduced to metallic silver with invert sugar in 

 a strong solution of sodic hydroxide. The silver thus obtained was 

 washed free from soluble matter and dissolved in nitric acid ; the argentic 

 nitrate after crystallization and whirling was reduced with ammonic 

 formate, yielding a beautiful crystalline mass of metal. 



This pure silver, after very thorough washing, was fused on lime by 

 means of a blast lamp whose tip had been carefully cleaned. The buttons 

 which were thus obtained were cooled in the reducing-flame, washed free 

 from lime, scrubbed with cleaned sea-sand, etched with strong nitric acid, 

 and washed with the purest water, to serve as anodes in the electrolytic 

 purification which was the next step. The electrolysis was carried on 

 as already described in previous similar Harvard researches, and every 

 step of the subsequent work may be found in detail in the preceding papers 

 on sodic and potassic chloride. 1 The metal was finally fused as usual on 

 a boat of the purest lime in an atmosphere of hydrogen under a tension of 

 50 mm. The larger pieces, after etching with nitric acid, were cut into 

 smaller ones of convenient size with a clean cold-chisel. They were again 

 etched in order to dissolve all traces of iron, 2 scrubbed with clean sand, 

 washed with a jet of water, and etched yet again with acid, paying par- 

 ticular attention to the cut edges. Finally the pieces were dried over an 

 alcohol lamp and kept in a desiccator over potassic hydroxide for use. 



This silver was used both in most of the titrations against potassic 

 bromide and as the source of argentic nitrate used in the precipitation of 

 argentic bromide to be weighed. 



a See Proc. Am. Acad.. 38. 450 (1903) : and Richards and Wells, Journ. Am. 

 Chem. Soc., 27, 473 (1905) ; Richards and Staehler, preceding paper. 



2 Richards and Archibald, Proc. Amer. Acad., 38, 450 (1903) ; Baxter, Journ. Am. 

 Chem. Soc., 28, 1329 (1906). 



