ATOMIC WEIGHTS 155 



COPPER. 



The atomic weight of copper has been chiefly determined by means of 

 the oxide, the sulphate and the bromide, and by direct comparison of 

 the metal with silver. 



In dealing with the first-named compound nearly all experimenters 

 have agreed in reducing it with a current of hydrogen, and weighing the 

 metal thus set free. 



The earliest experiments of any value were those of Berzelius,^ whose 

 results were as follows : 



7.68075 grm. CuO lost 1.55 grm. 0. 79.820 per cent. Cu in CuO. 



9.6115 " 1.939 " 79.826 



Mean, 79.823, ± .002 



Hence Cu = 63.298. 



Erdmann and Marchand," who come next in chronological order, cor- 

 rected their results for weighing in air. Their weighings, thus corrected, 

 give us the subjoined percentages of metal in CuO : 



63.8962 grm. CuO gave 51.0391 grm. Cu. 79.878 per cent. 



65.1590 " 52.0363 " 79.860 



60.2878 " 48.1540 "• 79.874 



46.2700 " 36.9449 " 79.846 



Mean, 79.8645, ± .0038 



Hence Cu = 63.462. 



Still later we find a few analyses by Millon and Commaille." These 

 chemists not only reduced the oxide by hydrogen, but they also weighed, 

 in addition to the metallic copper, the water formed in the experiments. 

 In three determinations the results were as follows : 



6.7145 grm. CuO gave 5.3565 grm. Cu and 1.5325 grm. HoO. 79.775 per cent. 



3.3945 " 2.7085 " .7680 " 79.791 



2.7880 " 2.2240 " .... " . 79.770 



Mean, 79.7787, ± .0043 



Hence Cu = 63.125. 



For the third of these analyses the water estimation was not made, 

 but for the other two it yielded results which, in sum, would make the 

 atomic weight of copper 63.165. This figure has so high a probable 

 error that we need not consider it further. 



iPoggend. Annal., S, 177. 1826. 

 2Journ. prakt. Chem., 31, 380. 1844. 

 ^ Fresenius' Zeitschrift, 2, 475. 1863. 



