CADMIUM. Ill 



series it was essential that the hydrogen should first be 

 thoroughly dried before combustion, and then that every 

 trace of water formed should be collected. A trivial loss of 

 hydrogen or of water would tend to increase the apparent 

 atomic weight of zinc. 



In the combustion of the zinc oxalate equally great diffi- 

 culties are encountered. Here a variety of errors are possi- 

 ble, such as arc due, for example, to impurity of material, 

 to imperfect drying of the carbon dioxide, and to incomplete 

 collection of the latter. It may not be easy to prove that 

 such errors actually did creep into Favre's work, and yet 

 their possibility hinders us from absolutely accepting his 

 results. 



All things considered, then, Erdmann's determination of 

 the atomic weight of zinc is the one most entitled to credit, 

 and must be taken for the present in lieu of the general 

 mean deduced from all four of the values. This determina- 

 tion, Zn = 64.9045, ± .019, becomes, if = 16, 65.054. 



CADMIUM. 



The earliest determination of the atomic weight of this 

 metal was by Stromeyer, who found that 100 parts of cad- 

 mium united with 14.352 of oxygen.* With our value 

 for the atomic weight of oxygen these figures make Cd = 

 111.227. This result has now only a historical interest. 



The more modern estimates of the atomic weight of cad- 

 mium are four in number, by v. ITauer, Lenssen, Dumas, 

 and Huntington. Of these that b}^ v. Hauerf comes first 

 in chronological order. He heated pure anhydrous cad- 

 mium sulphate in a stream of dry hydrogen sulphide, and 

 weighed the cadmium sulphide thus obtained. His results 



* See Berz. Lehrbuch, 5th Ed., 3, 1219. 

 f Journ. fiir Prakt. Chem., 72, 350. 1857. 



