Molybdenum, Vanadium, Selenium and Tellurium. 541 



In testing the reaction of a soluble yanadate with potassium 

 iodide an exactly analogous process to that used in the case of 

 molybdenum was carried out. The ammonium vanadate was 

 fused with sodium tungstate to determine the amount of vana- 

 dium pentoxide contained in it. A known amount of the 

 vanadate was shaken with potassium iodide , hydrochloric 

 acid, and the silver, and the results calculated on the assump- 

 tion that one molecule of vanadium pentoxide liberates two 

 atoms of iodine. The results shown in Table II would indi- 

 cate that the reaction takes place according to the equation : 



V 2 5 + 2HC1 + 2KI = Vfi i + H 2 + 2KC1 + I 2 . 







Table II. 



Calculated 





Ag taken 



V 2 5 taken 



I found 



v 2 o 5 



Error 



grin. 



grm. 



grm. 



grm. 



grm. 



2-0012 



0-1946 



0-2699 



0-1939 



— 0-G007 



2-0012 



0-2051 



0-2856 



0-2051 



±0-0000 



2-0024 



0-1964 



1 0-2746 



0-1972 



+ 0-0008 



2-0024 



0-2362 



0-3295 



0-2367 



+ 0-0005 



2-0062 



0-2953 



0-4106 



0-2949 



— 0-0004 



2-0062 



0-2681 



0-3729 



0-2679 



— 0-0002 



2-0527 



0-5110 



0-8038 



0-5774 



+ 0-0004 



2-0006 



0-2035 



0-2829 



0-2032 



— 0-0003 



With selenium and tellurium it was found that the reduc- 

 tion proceeded to the end, giving the free elements, so that in 

 weighing the residue of silver and silver iodide the amount of 

 selenium or tellurium taken was included. The results obtained 

 indicate that the reactions between selenium dioxide and potas- 

 sium iodide and between tellurium dioxide and potassium 

 iodide proceed according to the following equations : 



Se0 2 + 4KI + 4HC1 = 4KC1 + 2H 2 + Se + 2l 2 . 

 Te0 2 + 4KI + 4HC1 = 4KC1 + 2H 2 + Te + 2l 2 . 



The selenium used was carefully purified by twice crystaliz- 

 ing from nitric acid solution as selenium dioxide and resublim- 

 ing in the presence of manganese dioxide. Definite amounts 

 of a standard solution of selenium dioxide were added to an 

 excess of potassium iodide in acid solution, and shaken with a 

 weighed amount of the silver under the atmosphere of hydro- 

 gen. The increase in weight should represent the iodine 

 liberated plus the selenium taken. The results in Table III 

 were calculated upon the assumption that one molecule of 

 selenium dioxide liberates four atoms of iodine, which gives 

 13*49 per cent of the increase in weight as the amount of 

 selenium taken. 



