O RESEARCHES UPON ATOMIC WEIGHTS. 



platinum dish, and the solution of ammonium chloride was evaporated to 

 crystallization. 



The cadmium ammonium chloride was crystallized in a platinum dish, eight 

 times in the case of the first fraction, four times in the case of the second frac- 

 tion. The third fraction of the sulphide was not converted into the double 

 chloride, but was investigated in a later research upon cadmium bromide (see 

 page 2i). The first fraction is designated as Sample I, the second as 

 Sample II. 



A third specimen used in the analyses was a portion of that employed in the 

 determination of the specific gravity of cadmium chloride.^ This is designated 

 as Sample A. The method of purification of Sample A was almost exactly 

 identical with that described above, except that the original material was pre- 

 cipitated but not fractionated with hydrogen sulphide. 



SILVER. 



In the preparation of pure silver essentially the same method was employed 

 as in other atomic weight investigations in this laboratory .^ In this case the 

 various treatments consisted in thrice precipitating the silver from a dilute 

 solution of silver nitrate in nitric acid by a large excess of hydrochloric acid, 

 with intermediate reduction of the silver chloride in each case by means of 

 invert sugar and sodium hydroxide. The sodium hydroxide for the third re- 

 duction was freed from heavy metals by electrolysis. Both the silver chloride 

 and the metallic silver were of course very thoroughly washed by decantation 

 with pure water. The final product was fused on charcoal in the flame of a clean 

 blowpipe. Next the buttons were converted into electrolytic crystals by slow 

 deposition upon a pure silver cathode from a concentrated, nearly neutral solu- 

 tion of silver nitrate, the anode being composed of the pure silver buttons. 

 After thorough washing and drying the crystals were fused in a current of pure 

 electrolytic hydrogen in a boat of pure lime.^ The lime boat was made by 

 lining an unglazed porcelain boat with a mixture of freshly ignited lime and 

 calcium nitrate, both having previously been carefully freed from iron and other 

 heavy metals. The boat was thoroughly ignited before use.* During the fusion 

 it was contained in a large Royal Berlin porcelain tube, the ends of which were 

 closed with hollow brass stoppers made to fit tightly by means of narrow r'ngs 

 of rubber, the stoppers being cooled by a current of cold water,^ Richards and 

 Wells, in a recent investigation of the purity of silver purified by different 



^ Loc. cit. 



* See especially Richards and Wells: Pub. Car. Inst., No. 28, 16 (1905); Jour. Amer. 

 Chem. Soc, 27, 472; Zeit. anorg. Chem., 47, 70. 



' Baxter: Proc. Amer. Acad., 39, 249 (1903); Zeit. anorg. Chem., 38, 237 (1904). 



* Richards: Proc. Amer. Acad., 30, 379 (1894); Zeit. anorg. Chem., 8, 262 (1895); Rich- 

 ards and Parker: Proc. Amer. Acad., 32, 63 (1896); Zeit. anorg. Chem., 13, 89 (1897). 



' Richards and Parker: Loc. cit. 



