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



Art. XXIX. — The Estimation of Lead, Nickel, and Zinc 

 by Precipitation as Oxalates and Titration with Potassium 

 Permanganate ; by H. L. Ward. 



[Contributions from the Kent Chemical Laboratory of Yale Univ. — ccxxix.] 



Determination of Lead, 



Reis in some investigations on the use of oxalates in analysis 

 precipitated lead as the oxalate* by adding ammonium oxalate 

 to a neutral solution of a lead salt and breaking up the result- 

 ing soluble double oxalate with a large excess of acetic acid. 

 The insoluble lead oxalate was filtered off and ignited, and the 

 lead was weighed as the oxide. It was thought that lead oxa- 

 late precipitated under these conditions might be of such 

 composition that titration with permanganate would give a 

 true estimate of the amount of lead present. 



In the experiments of Table I the oxalate was precipitated 

 by the addition of solid ammonium oxalate to the boiling solu- 

 tion of lead nitrate, containing the amount of acetic acid spec- 

 ified. The precipitate was collected on asbestos in a perforated 

 crucible, and washed with small amounts of water. The oxalic 

 acid was then set free by treatment with warm dilute sulphuric 

 acid and titrated with potassium permanganate. 







Table I. 







The Detenu 



lination of Lead by Pn 

 in the Presence of 



Bcipitation with Ammonium 

 Strong Acetic Acid. 



Oxalate 



Lead present 

 as the 

 nitrate 



Volume 

 at precipi- 

 tation 



Acetic 



acid 



present 



Ammo- 

 nium 

 oxalate 



Lead 

 found 



Error 



grin. 



cm 3 



cm 3 



grin. 



grm. 



grm. 



0*0050 



100 



25 



3 



0-0016 



-0-0036 



0*0250 



100 



25 



3 



0-0246 



-0-0004 



0-0500 



100 



5 



3 



0-0454 



— 0-0046 



0-0500 



100 



10 



3 



0-0480 



— 0-0020 



0-0500 



100 



25 



3 



0-0496 



— 0*0004 



0-0500 



200 



50 



7 



0-0477 



— 0-0023 



0-0050 



100 



50 



4 



0-0048 



— 0-0002 



0-0050 



100 



50 



4 



0-0045 



— 0-0005 



0-0250 



100 



50 



4 



0-0256 



+ 0-0006 



0-0250 



100 



50 



4 



0-0250 



+ 0-0000 



0-0500 



100 



50 



4 



0-0505 



+ 0-0005 



o-iooo 



200 



100 



8 



0-1002 



+ 0-0002 



It will be noticed in the first part of the table, where the 

 amount of acetic acid does not exceed one-fourth of the solu- 



* Ber. Dtsch. Chem. Ges., xiii, 502. 



