Gooch and Beyer — Electrolytic Estimation of Lead. 61 



given the results of experiments following this procedure, and, 

 for comparison, the result of an experiment, (1) in which it 

 was found that, though electrolysis was continued by the cir- 

 culating process until the filtrate contained no lead, traces of 

 lead dioxide went into solution after the amount of electricity 

 which passed had been diminished by the gradual dilution with 

 water used in washing to replace the electrolyte. Tests for 

 lead in filtrates and washings were made by neutralizing with 

 ammonium hydroxide and adding ammonium sulphide, or 

 acetic acid and potassium chromate. 



Table I. 

 Electrolysis with Continuous Filtration. 



HN0 3 Current 



Pb(N0 3 ) 2 Vol. cone. , K ^ Time Pb0 2 Theory Error 



Amp. NDj oo Volt found for Pb0 2 



cm 3 . min. grm. grm. grm. 



A 

 With no ammonium nitrate in electrolyte or in wash-water. 

 (1) 0-2023 50 15 2 5 4 5 



4 10 5 130 0-1460 0-1436 —00024 



B 



With ammonium nitrate in electrolyte and in wash-water. 



(2) 



0-2022 



50 



15 



2 



5 



4 



40 















4 



10 



5 



100 



0-1459 0-1462 



+ 0-0003 



(3) 



0-2014 



50 



15 



2 



5 



4 



5 















4 



10 



5 



115 



0-1454 0-1458 



+ 0-0004 



W 



0-2001 



50 



15 



2 



5 



4 



5 















4 



10 



5 



115 



0-1444 0-1442 



— 0-0002 



00 



0-2006 



50 



15 



2 



5 



4 



5 















4 



10 



5 



115 



0-1448 0-1446 



— 0-0002 



(6) 



0-2046 



50 



15 



2 



5 



4 



5 















4 



10 



5 



115 



0*1477 0-1472 



— 0-0003 







With 



ammonium nil 



C 

 irate in 



wash-water only. 





(8) 



0-2020 



50 



15 



2 



5 



4 



5 















4 



10 



5 



115 



0-1458 0-1460 



+ 0-0003 



(9) 



0-2037 



50 



15 



2 



5 



4 



5 













4 



4 



10 



5 



115 



0-1470 0-1473 



+ 0-0003 



From the results of the experiments described, it appears 

 that good analytical results may be obtained with the filtering 

 crucible used as an electrolytic cell if nitric acid be present to 

 the proportion of 30 cm3 of the concentrated acid in 100 cm3 of 

 solution, the liquid kept in continuous filtration until the elec- 

 trolysis of the lead salt is complete, the acidic liquid replaced 

 by a solution of ammonium nitrate so that the electric current 

 passing shall not fall off until the nitric acid has been removed, 



