ATOMIC WEIGHTS 



161 



Hence, 



Cu. 



4 77886 



6 1.90973 



7 73380 



8 92344 



9 1.47926 



Cu:Na.CO,::100:x. 

 166.824 

 166.840 

 166.840 

 166.849 



1.2993 

 3.1862 

 1.22427 

 1..54075 



1.7411 

 4.2679 

 1.63994 



3.30658 



Ctr.Na,8O,::100:x 

 223.549 

 223.482 

 223.538 

 223.529 



Mean, 166.838, ± .0035 



Mean, 223.525, ± .0098 



Hence Cn = 63.55. Hence Cu = 63.571. 



In one more experiment the sulphuric acid was weighed as barium 

 sulphate, the latter being corrected for occluded salts. 3.1903 grm. 

 CuS0,.5H„0 gave 2.9761 BaSO^ ; hence CuS0,.5H,0 : BaSO,: : 100: 

 93.289. The sulphate contained 25.448 per cent, of Cu; hence BaSO^: 

 Cu : : 93.289 : 25.448, and Cu = 63.676. Still other ratios can be deduced 

 from Eichards' work on the sulphate, but in view of the uncertainties 

 relative to the water in the salt they are hardly worth computing. 



In his third paper upon the atomic weight of copper,^ Eichards studied 

 the dibromide, CuBr2. In preparing this salt he used hydrobromic 

 acid made from pure materials, and further purified by ten distillations. 

 This was saturated with copper oxide prepared from pure electrolytic 

 copper, and the solution obtained was proved to be free from basic salts. 

 .\s the crystallized compound was not easily obtained in a satisfactory 

 condition, weighed quantities of the solution were taken for analysis, in 

 which, after expulsion of bromine by nitric and sulphuric acids, the 

 copper was determined by electrolysis. In other portions of solution 

 the bromine was precipitated by silver nitrate, and weighed as silver 

 bromide. The first preliminary series of experiments gave the subjoined 

 results, with vacuum weights as usual : 



In 25 Grammes of Solution. 



Cu. AgBr. 



.4164 2.4599 



.4164 2.4605 



.4164 2.4605 



.4165 2.4599 



Hence 2AgBr : Cu : : 100 : 16.937, ± .0013. 



1 Proc. Amer. Acad., 25, 195. 1890. 



