THE GRAVIMETRIC DETERMINATION OF TELLURIUM. 
VICTOR LENHEK AND A. W. HOMBEEGER. 
Of all the methods proposed for the precipitation of tellurium 
perhaps the one which is most used is a modification of the 
original method of Berzelius. He used sulphurous acid as a 
precipitating agent. 
The method of procedure as commonly carried out consists in 
adding to the hydrochloric acid solution of tellurium a strong 
aqueous solution of sulphur dioxide and allowing this mixture 
to remain in a warm place for a few days in order to effect com' 
plete precipitation. It has been shown by Schroetter , 1 Braw- 
ner , 2 Norris and Bay , 3 Crane , 4 Brerichs , 5 and others that the 
precipitation by means of sulphur dioxide is far from satisfac¬ 
tory. Brawner has pointed out that part of the precipitated 
tellurium undergoes oxidation in the liquid becoming converted 
into the tetrachloride in which form it remains in solution. 
Crane has suggested that the main cause of the incomplete pre¬ 
cipitation by means of sulphur dioxide is the very rapid in¬ 
crease in the ratio of the acids to the unprecipitated tellurium 
in solution, two-thirds of this being due to the hydrochloric acid 
set free, and one-third to the sulphuric acid formed. He 
thought if these could be removed the reduction would be com¬ 
plete. The hydrochloric acid could be eliminated by evapora¬ 
tion, but the continuous increase in sulphuric acid would soon 
interrupt the reaction. This might, however, be kept under 
control by the addition of sodium or potassium hydroxide. 
1 Chem. News 87, 17. 
2 Jour. Chem. Soc. 55, 392. 
s Amer. Chem. Jr. 20, 278. 
4Amer. Chem. Jr. 23, 408. 
s Jr. fur pr. Chem. 66, 261. 
