272 Gooch and MorgoM — Determination of Tellurium, etc. 



one-fourth of its volume of strong sulphuric acid. The Erlen- 

 meyer beaker was placed upon a pane of window glass sup- 

 ported upon strips of wood about V^^ above the level of the 

 work table, which was covered with white paper. A solution 

 of approximately decinormai potassium iodide free from iodate 

 and carefully standardized in terms of iodine by a method 

 described in a former paper from this laboratory* was intro- 

 duced gradually from a burette into the middle of the Erlen- 

 meyer beaker. As the drops of the potassium iodide touched 

 the liquid the precipitation formed at the center and traveled in 

 rings toward the outer walls of the beaker. When the liquid 

 became so opaque that the effect of the potassium iodide was 

 distinguished with difficulty, the beaker was rotated and the 

 curded precipitate permitted to settle, and then the process of 

 titration was continued as before. We experimented with 

 amounts of tellurium dioxide varying from approximately 

 0*025 grm. to 0*1 grm., the latter quantity being as large as can 

 be handled with accuracy without intermediate removal of the 

 precipitate by filtration. With an Erlenmeyer beaker 10^°^ in 

 diameter across the bottom and a final volume of liquid 

 amounting to not more than 100 cm^, we were able to follow 

 the precipitation most easily. 



The results of a series of determinations made according to 

 the method described and recorded in the following table are 

 closely accordant, and, in close agreement with the theory of 

 the process if the atomic weight of the tellurium which we 

 used is taken as 127. We feel justified in taking this number 

 as the atomic weight of our tellurium, because the mean result 

 of twelve oxidations by standard potassium permanganate of 

 tellurium dioxide, prepared similarly to that which we used 

 and from the same lot of material, and the mean result of 

 twelve reductions by hydrobromic acid of the telluric acid thus 

 produced,f point to this figure. 



Final 



Strongest 



Iodine value 









volume. 



H2SO4 present. 



of KI used. 



TeOa taken. 



TeOa found 



. Error. 



cm 2 



cm3 



grm. 



grm. 



grm. 



grm. 



50 



17 



0-0706 



0-0223 



0-0221 



0-0002 — 



(( 



ii 



0-0764 



0-0244 



0-0239 



0-0005 — 



u 



(( 



0-1591 



0-0496 



0-0499 



0-0003 + 



60 



ii 



0-1655 



0-0517 



0-0519 



0-0002 + 



iC 



u 



0-1578 



0-0498 



0-0494 



0-0004- 



80 



so 



0-1591 



0-0498 



0-0499 



0-0001 + 



100 



a 



0-3179 



0-1001 



0-0997 



0-0004 — 



<( 



cc 



0-3186 



0-1008 



00999 



0-0009- 



it 



(S 



0-3208 



0-1011 



0-1005 



0-0006- 



(Z 



ct 



0-3208 



0-1010 



0-1005 



0-00C5 — 



From these results it is obvious that the method, which is 

 very rapid, is accurate. 



* This Journal, xxxix, 188 ; xlv, 334. \ Ibid,, xlviii, 377 and 378. 



