H. L. Ward — Estimation of Lead, Nickel, and Zinc. 337 



it was necessary to heat it to start precipitation. The nickel 

 oxalate was filtered off on asbestos in a perforated crucible 

 and washed with small amounts of water. The crucible was 

 placed in a beaker containing about 25 cm3 of dilute (1 : 4) sul- 

 phuric acid and heat applied to effect the solution of the oxa- 

 late. The volume of the solution was then made up to about 

 200 cm3 and cobalt sulphate added until a slight pinkish tinge 

 appeared. This procedure, recommended by Gibbs, was neces- 

 sary to secure a definite end-point, as the green color of the 

 nickel masked the complementary pink of the permanganate. 

 The contents of the beaker were then heated to boiling and 

 titration made in the usual manner. The results appear in 







Table III. 







The 



Determination of Nickel by Precipitation with Oxalic 

 and Treatment with Acetic Acid. 



Acid 



Nickel 



as 



sulphate 



Volume 



of water 



solution at 



precipitation 



Oxalic 

 acid 



Acetic 

 acid 

 added 



Nickel 

 found 



Error 



grm. 



cm 3 



grm. 



cm 3 



grm. 



grm. 



0-0503 



100 



2 



50 



0-0502 



—o-oooi 



0-0050 



100 



2 



100 



0-0054 



+ 0-0004 



0-0251 



100 



2 



100 



0-0258 



+ 0-0007 



0-0503 



50 



2 



100 



0-0514 



+ 0-0011 



0-0503 



100 



2 



100 



0-0502 



—o-oooi 



0-1257 ' 



100 



2 



100 



0-1271 



+ 0-0014 



Table III. The positive errors may be assigned to two causes, 

 inclusion of the precipitant and uncertainty of end-point when 

 titrating in colored solutions. 



Determination of Zinc as the Oxalate. 



It was found to be possible to estimate zinc volumetrically as 

 the oxalate by the process already outlined for nickel. In this 

 case, no colored salts being present in the solution on nitration, 

 a more definite end point was secured and the results obtained 



are much 



more accurate, as 



appears in Table IV. 









Table IV. 





The Determination 



of Zinc 



j by Precipitation with Oxalic Acid 





and Treatment with Acetic Acid. 





Zinc 



Volume 









as 



at 



Oxalic 



Acetic Zinc 





acetate 



precipitation 



acid 



acid found 



Error 



grm. 



cm 3 



grm. 



cm 3 grm. 



grm. 



0-0055 



100 



2 



100 0-0056 



+ 0-0001 



0*0274 



100 



2 



100 0-0276 



+ 0-0002 



0*0548 



50 



2 



50 0-0553 



+ 0-0005 



0-0548 



100 



2 



100 0*0550 



+ 0-0002 



0-1370 



100 



2 



100 0-1372 



+ 0-0002 



