G. S. Jamieson — Determination of Lead as Sulphite. 159 



In attempting to precipitate lead as sulphite in the presence 

 of copper it was observed that high results were always 

 obtained when following the directions given above. The 

 error was apparently due to the precipitation of some lead sul- 

 phate as the precipitates were found to be free from copper. 

 After much experimentation it was found that a satisfactory 

 separation of the lead could be obtained if care was taken to 

 filter the lead sulphite within about an hour after precipitation. 

 It was found best to filter the solution, leaving as much as 

 possible of the precipitate in the beaker. After washing the 

 precipitate once with about 10 co of water and decanting again, 

 it was heated for 5 minutes with 10-15 cc of a strong solution 

 of ammonium sulphite. Then the precipitate was transferred 

 to the crucible and washed thoroughly with water and dried. 

 The ammonium sulphite was prepared by passing sulphur 

 dioxide gas into a solution (1:1) of ammonium hydroxide 

 until it was strongly acid and adding enough more of ammonia 

 to neutralize the solution. 



The following results were obtained : 



Vo. Pb taken 



Cu taken 



Pb found 



Error 



1 



1004 



•1554 



•1014 



-f-ooio 



2 



1513 



•2331 



•1517 



+ •0004 



3 



1505 



•2331 



•1512 



+ •0007 



4 



0100 



•3885 



•0101 



+ •0001 



5 



1405 



•1941 



•1405 



•oooo 



6 



1405 



•1941 



•1413 



+ •0008 



7 



1204 



•2331 



•120] 



— •0003 



8 



1204 



•2331 



•1200 



— •0004 



Four analyses were made by simply adding an excess of 

 sodium bisulphite and allowing the precipitate to settle iu most 

 cases for several hours before filtration. 



Jo. 



Pb taken 



Cu taken 



Pb found 



Error 



1 



•1566 



•1554 



•1598 



+ •0032 



2 



•1566 



•1554 



•1606 



+ •0040 



3 



•0739 



•3885 



•0752 



+ •0012 



4 



•1471 



•2331 



•1499 



+ ■0020 



An attempt was made to determine lead as sulphite in the 

 presence of calcium, but calcium sulphite was found to be par- 

 tially precipitated along with the lead, although a calcium solu- 

 tion gave no precipitate with sodium bisulphite even after 

 standing two days. 



It was found that lead could be readily separated from zinc 

 as shown by the following experiments : 



