COPPER. 91 



COPPER. 



The atomic weight of copj^er 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 all experimenters have 

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

 metal thus set free. 



The earliest experiments of an}' value were those of Berzelius,* whose 

 results were as follows : 



7.6S075 grm. CuO lost 1.55 grm. O. '79.820 per cent. Cu in CuO. 

 9.6115 " 1.939 " 79.826 



Mean, 79.823, ± .002 



Erdmann and Marchand,t who come next in chronological order, 

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

 rected, 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 



Still later we find a few anah'ses by Millon and Commaille. X 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. H.,0. 79-775 per cent. 

 3.3915 " 2.7085 " .7680 " 79.791 



2.7880 " 2.2240 " 79.770 " 



Mean, 79.7787, rb .0043 



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

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

 the atomic weight of copper 62.680. This figure has so high a probable 

 error that we need not consider it further. 



The results obtained by Dumas § are wholly unavailable. Indeed, he 

 does not even publish them in detail. He merel}' sa3's that he reduced 

 copper oxide, and also effected the synthesis of tiie subsulphide, but with- 

 out getting figures which were wholly concordant. He puts Cu = 63.5. 



*Poggend. Annal., S, 177. 1S26. 

 t Journ. fiir Prakt. Chem., 31, 380. 1S44. 

 I Fresenius' Zeitschrift, 2, 475. 1S63. 

 I Ann. Chim. et Phys. (3), 55, 129. 1S59. 



