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



Determination of Nickel. 



Classen has shown* that nickel may be completely precipi- 

 tated by treating the soluble nickel potassium oxalate with a 

 large amount of acetic acid. The oxalate formed under these 

 circumstances may be ignited to the oxide and weighed as such. 

 It seemed desirable to determine whether this oxalate is of such 

 composition as to allow the estimation of nickel by titrating 

 the oxalate radical with potassium permanganate. The pro- 

 cedure first tried was that recommended by Classen. To a 

 solution of a known amount of nickel sulphate was added a con- 

 siderable excess of potassium oxalate and the liquid heated to 

 boiling, when the oxalate first formed went into solution as 

 nickel potassium oxalate. Two volumes of acetic acid were 

 then added to precipitate the nickel oxalate. It was found 

 necessary, in order to secure a product which could be filtered, 

 to heat the acetic acid and to run slowly, with constant stir- 

 ring, into the boiling solution of the double salt. Upon this 

 treatment a flock y precipitate formed, which on standing 

 for some time at 60°-70° went over to a fine powder. By 

 filtration and titration with permanganate it was discovered 

 that the oxalate obtained under these conditions had a tendency 

 to include some of the precipitant, causing high results on 

 titration. On ignition also large positive errors were obtained, 

 but if the oxide was washed to remove the potassium carbonate 

 formed, a very good estimation of the amount of nickel present 

 was secured. 



It seemed possible that the use of oxalic acid as a precipitant 

 might eliminate the errors due to inclusion, but it was found 

 that if oxalic acid was added to the boiling solution of a nickel 

 salt containing an equal volume of acetic acid, the oxalate 

 formed came down quickly and in an extremely finely divided 

 condition. The first experiment of Table III was made in this 

 manner, but in the majority of instances filtration proved to be 

 impossible. If, however, precipitation was made in water solu- 

 tion and acetic acid added later to throw out the last traces of 

 nickel, the oxalate came out more slowly and in a form suitable 

 for filtration. 



The nickel sulphate taken for analysis was dissolved in water 

 and the solution standardized both by precipitation as nickelic 

 hydroxide and ignition to the oxide and by throwing out as 

 metallic nickel on the rotating cathode. To a definite amount 

 of this solution, diluted to the required volume and heated to 

 boiling, was added an excess of crystallized oxalic acid. Upon 

 cooling, acetic acid was run in and the precipitate allowed to 

 settle over night. The smaller amounts of nickel did not come 

 out from the water solution, and even after adding acetic acid 



* Classen, Zeitschr. anal. Chem., xvi, 470. 



