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



Another series of experiments was made using measured 

 quantities of a lead nitrate solution which contained 7"3950 

 grams of lead and 5 grams of actual nitric acid in 1000 cc . The 

 lead was precipitated with a solution of sulphurous acid which 

 contained 36*8 grams of sulphur dioxide per liter. In some of 

 the experiments, sodium acetate was added after precipitating 

 the lead sulphite, as indicated in the following table of analyses : 





cc of Pb 





Wt. of 







NaC 2 H 3 2 



ce of 



No. 



sol. Pb taken 



PbS0 3 Pb found 



Error 



sol. 10# 



S0 2 



1 



20-15 



•1489 



•2071 



1493 



+ •0004 







18 



2 



15-0 



•1108 



•1530 



1106 



— •0002 







15 



3 



25-0 



•1850 



•2550 



1839 



— •0011 







20 



4 



20 ; 05 



•1482 



•2056 



1483 



+ •0001 



10 



15 



5 



25-10 



•1856 ' 



•2576 



1858 



— •0002 



10 



18 



6 



25-0 



•1850 



•2563 



1848 



— •0002 







18 



7 



20-0 



•1478 



•2045 



1475 



-•0003 







18 



8 



10-0 



•0739 



•1027 



0740 



+ ■0001 



10 



8 



9 



10-1 



0747 



•1034 



0746 



— •0001 



10 



16 



10 



10-0 



•0739 



•1027 



0740 



+ •0001 



20 



24 



In the first three analyses given above the lead sulphite was 

 filtered ten minutes after adding the sulphurous acid. In experi- 

 ments 8 and 9 the precipitates were allowed to settle an hour 

 before filtration, while the others were allowed to stand over 

 night. In dealing with unknown quantities of lead and free 

 acid, it is safer to add some sodium acetate. Also it should be 

 observed that it is possible to have such an excess of sulphur- 

 ous acid that it will exert a solvent action on the lead sulphite. 



Several experiments were made in order to determine the 

 conditions under which it would be possible to precipitate lead 

 sulphite quantitatively from solutions containing considerable 

 free acid. It was found that it was only necessary to neutra- 

 lize the free acid with ammonium hydroxide. However the 

 solution should be left slightly acid so that when the lead is 

 precipitated it will separate in a satisfactory 7 condition for fil- 

 tration. 



The following results were obtained by precipitating the 

 lead with a solution of sodium bisulphite after the acid (10 cc 

 HN0 3 ) had been nearly neutralized : 







Wt. of Pb 







No. 



Pb taken 



S0 3 



Pb found 



Error 



1 



■1117 



•1554 



•1120 



+ ■0003 



2 



•1479 



•2049 



•147S 



— •0001 



3 



•1845 



•2565 



•1849 



+ •0003 



4 



•1482 



•2060 



•1485 



+ •0003 



5 



•1479 



•2046 



•1476 



— •0003 



