Gooch and Bosworth — lodometric Estimation of Silver. 303 



portions successively. The filtrate was treated with potassium 

 iodide and acidified with sulphuric acid. The iodine set free 

 was titrated with sodium thiosulphate. The difference be- 

 tween the silver value of the iodine thus found and that of the 

 potassium dichromate used was taken as the measure of the 

 silver present. In Table I are given the details of experiments 

 performed in accordance with this procedure. 



In Table II are given the details of similar experiments in 

 which the precipitation was effected in the presence of sodium 

 nitrate. 









Table II. 









Silver taken. 













Volume 





K 2 Cr< 







Error in 



of solu- 

 tion 







> , NflKOo 



Na 2 S 2 3 

 used 



Silver 

 found 



terms of 

 silver 



Weight 



Volume 



*\ J-ICUJNW3 



Weight present 



cm 3 . 



grm. 



cm 3 . 



grm. grm. 



cm 3 . 



grm. 



grm. 



10 



o-noi* 



37 



02436* 1 



20-47* 



0-1107 



— 0-0006 



10 



o-noi 



37 



0-2436 1 



20-53 



0-1103 



+ 0-0002 



10 



o-iioi 



25 



0-1647 1 



9-07 



0-1097 



— 0-0004 



10 



o-noi 



27 



0-1778 1 



11-02 



0-1096 



— 0-0005 



15 



0-0862f 



+ 30 



0-1974* 2 



17-14* 



0*0859 



— 0-0003 



15 



0-0862 



30 



0-1974 1 



17-05 



0-0865 



+ 00003 



15 



0-0862 



30 



0-1974 1 



17-14 



0-0859 



— 0-0003 



25 



0-1437 



50 



0-3294 10 



28-53 



0-1435 



— 0-0002 



* Approximately N/10. 



f Approximately N/20. 



Since, as has been shown in the paper previously referred 

 to, relatively large amounts of potassium chromate are neces- 

 sary to bring about complete precipitation of the silver chro- 

 mate in the presence of nitric acid, the above procedure 

 seemed less adapted to the determination of silver in a solution 

 containing that acid than the method whereby the precipitated 

 and washed silver chromate is determined. The following is 

 an account of the results obtained in the study of this latter 

 procedure. To the silver solution containing free nitric acid, 

 potassium chromate was added in excess of the amount necessary 

 to take up the nitric acid with formation of potassium dichrom- 

 ate. The precipitate was dissolved in ammonia and reprecipi- 

 tation effected by boiling to a volume of 10-15 cm3 * The second, 

 crystalline precipitate was transferred to an asbestos filter by 

 means of a dilute solution of potassium chromate, washed with 

 the least possible amount of water applied in small portions 

 successively, and dissolved in a few cm 3 of a strong solution of 

 potassium iodide. The solution in potassium iodide was diluted 

 and acidified with sulphuric acid. The iodine set free was 

 titrated with sodium thiosulphate and taken as the measure of 



