COPPER. 135 



COPPER. 



The atomi=c weight of copper has been chiefly determined 

 from the composition of the black oxide and the anhydrous 

 sulphate. 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 any value were those of Ber- 

 zelius,* whose results were as follows : 



7.6i>o75 gmi. CuO lost 1.55 grm. O. 79.820 per cent. Cu in CuO. 



9.61 15 " 1.939 " 79.826 



Mean, 79.823, dr .002 



Erdmann and Marchand,t who come next in chronologi- 

 cal order, corrected 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-^74 



46.2700 " 36.9449 " 79-846 " 



Mean, 79.8645, ± .0038 



Still later we find a few analyses by Millon and Com- 

 maille.i These chemists not onl}^ reduced the oxide by 

 hydrogen, but they also weighed, in addition to the metallic 

 copper, the water formed in the experiments. In three de- 

 terminations the results were as follows : 



6.7145 grm. CuO gave 5.3565 grm. Cu and 1.5325 grm. H^O. 79.775 per cent. 

 3.3945 " 2.7085 " .7680 " 79.791 " 



2.7880 " 2.2240 grm. Cu. 79-770 " 



Mean, 79.7787, =fc .0043 



For the third of these analyses the water estimation was 

 not made, but for the other two it yielded results which, in 



* Poggend. Annal., 8, 177. 



f Journ. fiir Prakt. Chem., 31, 389. 1844. 



J Fresenius' Zeitschrift, 2, 475. 1863. 



