22 UNIVERSITY OF COLORADO 



ify with HC1, warm, and filter. Wash the ppt. into a beaker, 

 rinse the filter paper with a hot concentrated solution of oxalic 

 acid (in which stannic sulphides are soluble), boil, and filter. Add 

 nitric acid, boil until red fumes cease (oxalic goes to carbonic acid), 

 evaporate to dryness, take up in yellow ammonium sulphide, re- 

 precipitate with HC1, filter into a Gooch crucible and ignite in the 

 muffle. Weigh as Sn0 2 . 



There are three ways of getting rid of oxalic acid in the above 

 — by permanganate of potassium, by sulphuric acid, by nitric acid. 

 The latter is to be preferred, because nitric acid is a volatile acid, 

 and can be evaporated. 



