6-4 Gooc/i and Beyer — Electrolytic Estimation of Lead. 



Table II. 



Solution H0SO4 Theory Mn0 2 Mn0 2 



of M11SO4 co'nc. Current for weighed weighed Error 



taken , * » Mn0 2 as Mn0 2 as Mn 3 4 



cm 3 cm 3 Amp. ND. 100 Volt grm. grm. grm. 



A 



Electrolysis with continuous filtration. 



(1) 50 0'17 2 5 20—12 0-18G0 0*1862 +0-0002 



0-1858 —0-0002 



(2) 50 0-17 2 5 20—12 0'1860 0'1856 —0-0004 



0-J856 —0-0004 



(3) 50 0-17 2 5 20 — 12 0*1860 0*1843 —0*0017 



0*1872 +0*0012 

 B 

 Electrolysis in closed cell with subsequent filtration. 



(4) 50 0-17 2 5 20—12 0'1860 0*1860 0*0000 



0-1853 —0-0007 



(5) 50 0-17 2 5 20 — 10 0-1860 0'1856 — 0'0004 



0-1856 —0*0003 



(6) 50 0-17 2 5 18 — 10 0-1860 0'1853 -0-0007 



0-1858 0-0002 



Somewhat greater regularity in results might be expected if 

 the manganese dioxide could be converted to manganous sul- 

 phate and weighed as such, but experiments made with this 

 end in view were unsuccessful. The application of gaseous 

 sulphur dioxide proved to be ineffective and sulphuric acid 

 attacked the asbestos felt during ignition, causing a permanent 

 increment of weight. The substitution of spongy platinum 

 for asbestos in the filtering crucible, as suggested and used by 

 Monroe,* served to obviate the difficulty due to the action of 

 the sulphuric acid upon the filtering medium, but the process 

 of removing the necessary excess of sulphuric acid by gentle 

 heating over radiator was exceedingly slow and, if pushed, 

 liable to errors of mechanical loss. To weigh as either form 

 of oxide, in this process, is therefore better than to attempt the 

 conversion to manganese sulphate. 



The processes demonstrated for the electrolytic deposition 

 of lead dioxide and manganese dioxide with the use of the 

 filtering crucible are obviously inferior in point of convenience 

 to the more rapid processes which demand the use of large and 

 special platinum containers and rotating motors, but in absence 

 of such apparatus they may serve a useful purpose. 



* Chem. News, lviii, 101. 



