ATOMIC WEIGHTS 



401 



Hence Te = 126.81, a figure which falls below the atomic weight of 

 iodine. The error which suggests itself is the possible retention of 

 water or mother liquor by the telluric acid; but Marckwald obtained an 

 acid of constant weight after prolonged drying over phosphorus pent- 

 oxide. Still, water may have been retained as an enclosure within the 

 particles of acid, so enveloped as to be prevented from escaping. Marck- 

 wald's figures combine with other similar determinations thus : 



Staudenmaier 69.440, ± .0024 



Heberlein 69.381, ± .0115 



Marckwald 69.393, ± .0035 



General mean 69.424, ± .0020 



Lenher's investigations,' like those of his recent predecessors, had 

 special reference to the homogeneity of tellurium. The tellurium was 

 obtained from three distinct sources; first, from the telluride ores of 

 Colorado; second, from the residues of an electrolytic copper refinery; 

 and third, from Bohemian material. From these the double bromide 

 KjTeBrg was prepared, and this, by heating first in chlorine and after- 

 wards in gaseous hydrochloric acid, was converted into potassium chloiide. 

 That is, the ratio K2TeBrg:2KCl was measured, all weights being re- 

 duced to a vacuum. In the following table I have treated the three 

 series as one, for the results obtained are sensiblv uniform : 



Mean, 21.7596, ±.00017 



Hence Te = 127.57. 



* Joun. Anier. Chem. Soc, 31, 20. 1909. See also Lenher's figures for TeOo, previously cited. 



