540 



Perkins — Use of Silver in the Determination of 



Art. XLYI. — The Use of Silver in the Determination of 

 Molybdenum, Vanadium, Selenium and Tellurium • by 

 Claude C. Perkins. 



[Contributions from the Kent Chemical Laboratory of Yale Univ. — ccxi.] 



In former papers from this laboratory a process for the 

 gravimetric determination of free iodine by means of specially 

 prepared electrolytic silver* and the application of the same 

 process to the determination of combined iodine and other 

 halogens and the estimation of those oxidizers! whose reaction 

 with potassium iodide is definitely known to set free iodine 

 quantitatively have been described. The object of the work 

 described in the present paper was the application of the same 

 process to the determination of some of the rarer elements and 

 the study of the reaction of their oxides upon hydriodic acid in 

 the presence of silver. 



To test the reaction of a soluble molybdate upon combined 

 iodine in the presence of silver, a standard solution was made 

 from a weighed amount of ammonium molybdate in which the 

 percentage of molybdenum trioxide had been determined by 

 fusing with a weighed amount of sodium tungstate which con- 

 tained just enough tungstic acid to insure the absence of car- 

 bon dioxide. The ammonia was thus driven off and the 

 amount of molybdenum trioxide was found from the increase 

 in weight of the sodium tungstate.J Definite amounts of this 

 solution were added to an excess of potassium iodide, made 

 acid with hydrochloric acid and shaken with the electrolyti- 

 cally prepared silver under an atmosphere of hydrogen. From 

 the increase in weight of the silver the amount of molybdenum 

 trioxide was calculated on the assumption that one molecule of 

 molybdenum trioxide liberates one atom of iodine with the 

 results shown in Table I. These results would tend to show 

 that the reaction takes place according to the following equa- 

 tion : 



2Mo0 8 + 4KI + 4HC1 - 2Mo0 2 I + 4KC1 + 2H 2 + 1 2 . 

 Table I. 



Calculated 

 Ag taken M0O3 taken I 2 found M0O3 



grm. grm. grm. grm. 



2-0002 0-2127 0-1869 0*2120 



2 0006 0-2127 0-1874 0'2126 



2-0012 0-2127 0-1870 0'2121 



2-0048 0-2127 0'1876 0'2128 



2-0000 0-2540 0'2242 0*2543 



2-0004 0-2909 0-2571 0'2916 



* This Journal, vol. xxviii. 33, 1909. f Th -i s Journal. 

 % Gooch and Norton, this Journal, vol. vi, 168, 1896. 



Error 

 grm. 



— 0-0007 



—o-oooi 



• —0-0006 

 + 0-0001 

 + 0-0003 

 + 0-0007 



vol. xxix, 338, 



1910. 



