302 Goooh and Bosworth — Iodometric Estimation of Silver. 



Art. XXIII. — A Method for the Iodometric Estimation of 

 Silver Based upon the Use of Potassium Chromate -as a 

 Precipitant y by F. A. G-ooch and Rowland S. Bosworth. 



[Contributions froni the Kent Chemical Laboratory of Yale Univ. — cxcvii.] 



It lias been shown in a previous paper that with proper pre- 

 cautions silver may be precipitated and accurately estimated as 

 silver chromate. It was found that the addition of a sufficient 

 excess of potassium chromate to a solution of silver nitrate, 

 even in the presence of small amounts of nitric acid, brings 

 about a complete precipitation of the silver as silver chromate, 

 and that the precipitate thus obtained may be transferred to 

 the asbestos filter by means of a dilute solution of potassium 

 chromate and washed with small amounts of water without 

 appreciable loss of silver chromate. Upon the basis of such 

 exact precipitation of silver chromate by potassium chromate 

 it should be possible to establish a method for the iodometric 

 estimation of silver either by the estimation of the chromic 

 acid ion of the precipitated and washed silver chromate or by 

 the determination of the chromic acid ion of the potassium 

 chromate which remains after the precipitation of the silver 

 salt by a known amount of standard potassium chromate. 



In studying the latter procedure a known amount of stand- 

 ard potassium chromate in excess of the amount needed to 

 precipitate the silver was added to the solution of silver nitrate. 

 The precipitate was dissolved in ammonia and reprecipi- 

 tation brought about by boiling to a volume of 10-15 cm \ The 

 second, crystalline precipitate was filtered upon asbestos and 

 washed with the least possible amount of water applied in small 







Table I. 







Silver taken. 











Volume 











Error in 



of solu- 





K 2 Cr0 4 



Na 2 S 2 3 



Silver 



terms of 



tion 



Weight 



used 



used 



found 



silver 



cm 3 . 



grm. 



grm. 



cm 3 . 



grm. 



grm. 



20 



0-1261 



0-3039 



26-54 



0-1262 



+ 0-0001 



25 



0'1576 



0-3039 



22-61 



0-1575 



—o-oooi 



15 



0-0946 



0-3293 



30-51 



0-0946 



o-oooo 



15 



0-0946 



0-3293 



30-60 



0-0940 



— 0-0006 



15 



0-0946 



0-3293 



30-57 



0-0941 



— 0-0005 



15 



0-0946 



03293 



30-55 



0945 



— 0-0003 



19 98 



0-1260 



0-3293 



32-20 



0-1255 



— 0-0005 



20 



0-1261 



0-3293 



32-09 



0-1263 



+ 0'0002 



20 



0-1261 



0-3293 



32-10 



0-1263 



+ 0-0002 



25 



0-1576 



0-3293 



27-30 



0-1576 



o-oooo 



