PREPARATION OF THE MATERIAL. 13 



(c) Five extra precipitations with hydrochloric gas (or twelve in all) 

 yielded this salt, which was prepared for analysis in the same way as a. 



(d) This salt bore the same relation to c that b bore to a, being essen- 

 tially identical with c. 



(e) For this sample and the next one the nitrate was recrystallized 

 twelve times, and the chloride precipitated seven times. 



(/) From the final mother liquor of e, f was prepared, as b followed 

 after a. 



(2) This sample was exactly like a, except that the raw material came 

 from an entirely different source. 



ARGENTIC NITRATE. 



The nitrate of silver used for precipitating chlorine in the analysis was 

 crystallized three times from pure dilute nitric acid solution and each 

 time centrifugally freed from mother liquor. Before each analysis the 

 aqueous solution of the salt was tested in the nephelometer 1 for a possible 

 trace of argentic chloride, and no material was ever used which showed 

 to this exceedingly sensitive test the least trace of impurity. For preser- 

 vation in a pure state it was kept in a tight desiccator over potash. 



SILVER. 



The metallic silver used in the research was made from argentic nitrate 

 which had been six times recrystallized. The metal was precipitated as 

 fine powder by ammonic formate, 2 melted on pure lime, and further 

 purified by electrolysis. 3 The beautiful crystals thus prepared were fused 

 in a stream of pure electrolytic hydrogen and finally in a vacuum of 

 0.1 mm. The metal was supported on a boat of the purest lime, prepared 

 from calcic carbonate precipitated from the nitrate for this purpose. 

 The boat was provided with several compartments, each of which held 

 enough silver for one analysis, in order to avoid the possible introduc- 

 tion of impurity into the metal by subsequent cutting. It was inclosed 

 in a stout porcelain tube, provided with Hempel water-cooled stoppers, 

 and was heated electrically in a Heraeus tube-furnace. 4 The vacuum 

 was maintained by a motor-driven Geryk oil air-pump. Except for these 

 minor improvements, the preparation was essentially similar to the best 

 methods employed by Richards and Wells in their often-cited work, to 

 which the reader is referred for further details. 



JRichards, Proc. Am. Acacl., 30, 385 (1894) ; Zeit. anorg. Chem., 8, 269 (1895). 

 'Richards and Wells, Journ. Am. Chem. Soc., 27, 475 (1905). 

 3 J. L. Hoskyns Abrahall, Journ. Chem. Soc. Trans. (1892), 660; also Richards. 

 Proc. Am. Acad., 28, 22 (1893). 



4 Heraeus, Zeit. f. Elektrochemie, 8, 201 (1902). 



