542 



Perkins — Determination of 'Molybdenum -, etc. 







Table III. 







Ag taken 



Se taken 



Increase 



Calculated Se 



Error 



grm. 



grm. 



grm. 





grm. 



grm. 



2*0133 



0-0050 



0-0365 





0-0049 



—o-oooi 



2-0133 



0-0075 



0-0529 





0-0071 



— 0-0004 



2-5639 



0-0126 



0-0894 





0-0121 



— 0-0005 



2-5639 



0-0428 



0-3178 





0-0429 



+ 0-0001 



3-0018 



0-0504 



0-3799 





0-0501 



— 0-0003 



In determining tellurium the dioxide was prepared from the 

 basic nitrate by heating to drive off the nitric acid and the 

 residual tellurium dioxide was heated to constant weight. 

 Definite amounts of a standard solution, made from this product 

 of tellurium dioxide, were added to an excess of a solution of 

 potassium iodide, made acid with hydrochloric acid, and the 

 whole shaken with a weighed amount of the silver under an 

 atmosphere of hydrogen. The increase in weight represents 

 the iodine set free plus the amount of tellurium taken. The 

 results in Table IY were calculated upon the assumption that 

 one molecule of tellurium dioxide liberates four atoms of iodide 

 which gives 20-07 per cent of the increase as tellurium. 







Table IV. 











Te = 127-5 







Lg taken 



Te taken 



Increase 



Calculated Te 



Error 



grm. 



grm. 



grm. 





grm. 



grm. 



2-0152 



0-0330 



0-1654 





0-0332 



+ 0-0002 



2-0152 



0-0990 



0-4931 





0-0989 



—o-oooi 



2-0815 



0-0528 



0-2635 





0*0529 



+ 0-0001 



2-0815 



0-0660 



0-3294 





0-0661 



+ 0-0001 



2-0815 



0-0990 



0-4948 





0-0993 



+ 0-0003 



2-1693 



0-1650 



0-8240 





0-1654 



+ 0-0004 



3-0126 



0-1650 



0-8258 





0-1657 



+ 0-0007 



3-0126 



0-0660 



0-3302 





0-0663 



+ 0-0003 



The results show that molybdenum, vanadium, selenium, 

 and tellurium, may be determined gravimetrically by making 

 use of the reaction of their oxides in liberating iodine from 

 potassium iodide in an acid solution and combining the free 

 iodine with the specially prepared silver. 



