ATOMIC WEIGHTS 387 



In 1879, with direct reference to Mendeleef's theory, the subject of 

 the atomic weight of tellurium was taken up by Wills/ The methods 

 of Berzelius and von Hauer were employed, with various rigid precau- 

 tions in the way of testing balance and weights, and to ensure purity of 

 material. In the first series of experiments tellurium was oxidized by 

 nitric acid to form TeO,. The results gave figures ranging from Te = 

 126.64 to 129.66: 



2.21613 grm. Te gave 2.77612 grm. TeO,. 79.828 per cent. Te. 



1.45313 " 1.81542 " 80.044 



2.67093 " 3.33838 " 80.007 



4.77828 " 5.95748 " 80.207 



2.65029 " 3.31331 " 79.989 



Mean, 80.015, ± .041 



Hence Te = 128.12. 



In the second series tellurium was oxidized by aqua regia to TeO,. with 

 results varying from Te = 128.10 to 128.32: 



Hence Te = 128.22. 



By von Hauer^s process, the analysis of TeBr^.2KBr, Wills' figures 

 give results ranging from Te = 126.36 to 127.90. Reduced to a common 

 standard, 100 parts of the salt yield the quantities of AgBr given in the 

 third column : 



1.70673 grm. K„TeBre gave 2.80499 grm. AgBr. 164.349 



1.75225 " 2.88072 " 164.398 



2.06938 " 3.40739 " 164.657 



3.29794 " 5.43228 " 164.717 



2.46545 " 4.05742 " 164.571 



Mean, 164.538, ± .048 



Hence Te = 127.10. 



Combined with von Hauer's mean, 164.408, ±.045, this gives a general 

 mean of 164.468. ±.0324. 



The next determinations in order of time were those of Brauner.' 

 This chemist tried various unsuccessful methods for determining the 



iJourn. Chem. Soc, Oct., 1879, p. 704. 

 2Joum. Chem. Soc, 55, 382. 1889. 



