TELLURIUM. 271 



TELLURIUM. 



Particular interest attaches to the atomic weight of tellurium on ac- 

 count of its relations to the periodic law. According to that law, tellurium 

 should lie between antimony and iodine, having an atomic weight greater 

 than 120 and less than 126. Theoretically, Mendelejeff assigns it a value 

 of Te = 125, but all of the best determinations lead to a mean number 

 higher than is admissible under the currently accepted hypotheses. 

 Whether theory or experiment is at fault remains to be discovered. 



The first, and for many years the only, determinations of the constant 

 in question were made by Berzelius.* By means of nitric acid he oxi- 

 dized tellurium to the dioxide, and from the increase in weight deduced 

 a value for the metal. He published only his final results, from which, 

 if = 100, Te =^ 802.121. The three separate experiments give Te = 

 801.74, 801.786, and 802.838, whence we can calculate the following per- 

 centages of metal in the dioxide : 



80.057 



80.036 



80.034 



Mean, 80.042, zh .005 



The next determinations were made by von Hauer,t who resorted to 

 the analysis of the well crystallized double salt TeBr^.2KBr. In this 

 compound the bromine was estimated as silver bromide, the values 

 assumed for Ag and Br being respectively 108.1 and 80. Recalculating, 

 with our newer atomic weights for the above-named elements, we get 

 from von Hauer's anal3'ses, for 100 parts of the salt, the quantities of AgBr 

 which are put in the third column : 



2.000 grm. K.,TeBrg gave 69.946 per cent. Br. 164.460 



6.668 " 698443 " 164.221 



2.934 " 69.9113 " 164.379 



3.697 " 70.0163 " 164.626 



1. 000 " 69.901 " 164.355 



Mean, 164.408, ± .045 



From Berzelius' series we may calculate Te= 127.366, and from von 

 Hauer's Te = 126.454. Dumas, ;{: by a method for which he gives abso- 

 lutely no particulars, found Te = 129. 



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

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



*Poggend. Annalen, 28, 395. 1833. 

 + Sitzungsb. Wien Akad., 25, 142. 

 X Ann. Chim. Phys. (3), 55, 129. 1859. 

 g Journ. Chem. Soc, Oct., 1879, p. 704. 



