276 Flora — Estimation of Cadmium taken as the Sulphate. 



was unable to adapt this method to the rotating cathode. 

 When potassium formate was present in even the smallest 

 amounts the precipitate was spongy, and non-adherent. From 

 solutions containing formic acid alone, however, the metal is 

 deposited in a satisfactory form, but only after long passage of 

 the current. The following results will show the limit of 

 applicability of the process, experiments numbered 8 and 9 

 seeming to represent the most desirable conditions : 





Cd. 



KCHOo 













Cd. 







tkn. 



sat. sol. 





Cur't = 



N.'Dioo. 



E.M.F. 



Time 



fd. 



Error. 



No 



grm. 



cm 3 . 



HOCHO. 



amp. 



amp. 



vts. 



min. 



grm. 



grm. 



1. 



0-1019 



2 



__ 



1-0 -2-0 



3-6 



8 



17 



^1 Not weighed ; 



2. 



0'1223 



0-5 





0-4 



1*2 



8 





1 ppt. 

 f and 



blistered 



3. 



0-1223 



0-5 





0'4 



1-2 



8 





dropped 



4. 



0-1223 



0-5 





0-4 



1-2 



8 





J off. 





5. 



0-1223 





15 dps. 



0-25-0-8. 



0-75-2-4 



12 



25 



0-1228 



+ 0*0005 



6. 



0-1223 







15 " 



0*25-0-8 



0-75-2-4 



8 



25- 



0-1212 



— 0-0010 



7. 



0-1223 



__ 



21 " 



0-5 -1-5 



1-5 -4-5 



12-16 



35 



0-1202 



— 0-0021 



8. 



0-1019 





]-5 cm3 



0-5 -1-0 



1-5 -3-0 



12 



60 



0-1022 



+ 0-0003 



9. 



0-1223 







1-5 " 



0-4 -1-0 



1-2 -3-0 



12 



55 



0-1218 



— 0-0005 



In the experiments numbered 5, 6 and 7 the cadmium was 

 not all precipitated in the time indicated, as was shown by 

 testing the solution with hydrogen sulphide. 



IX. In Solutions containing Tartrates. 



Solutions containing ammonium tartrate were also tried, but 

 failed to give satisfactory deposits, the deposit in each case 

 being spongy. If the solution contain only tartaric acid, how- 

 ever, in place of its salts, fairly satisfactory results may be 

 obtained, as shown by the following table : 





Cd. 



Tartaric 

















tkn. 



acid. 



Cur't = 



N.Dxoo. 



E.M.F. 



Time. 



Cd. fd. 



Error. 



No 



• grm. 



grm. 



amp. 



amp. 



vts. 



min. 



grm. 



grm. 



1. 



0-1223 



3 



0-5-1-0 



1-5-3-0 



8 



20 



0-1212 



-o-ooii 



2. 



0-1223 



2 



0-5 



1-5 



8 



30 



0-1216 



— 0-0007 



3. 



0-1223 



2 



0-5 



1-5 



8 



50 



0-1215 



— 0-0008 



4. 



0-1019 



3 



1-5 



4-5 



11-8 



18 



0-1022 



+ 0-0003 



Tests with hydrogen sulphide showed that the cadmium was 

 not all precipitated in the tests numbered 1, 2 and 3, which 

 were performed at a dilution of 70 cm3 ; experiment 4 was per- 

 formed at a dilution of 50 cm3 . It will be noted that, as in the 

 sulphate process, the last traces of cadmium are thrown out of 

 the higher state of dilution only with extreme difficulty. 



