426 B. L. Ward — Oxalate- Permanganate Process. 



of whose volume is glacial acetic acid containing free nitric 

 acid. The oxalic acid is added in the solid form to the boiling 

 solution and the resulting oxalate allowed to stand over night. 

 Filtration, washing and titration are made in the same manner 

 as in the former method. 



It will be noticed that in the first part of Table III, where 

 small amounts of oxalic acid have been used in the precip- 

 itation, the results have a tendency to come low, especially 

 when the larger amounts of nitric acid are present. At least 

 3*5 grm. to 4 grm. of oxalic acid should be used for every 

 100 cm3 of solution, but more causes trouble by crystallizing out. 

 It is then necessary to dissolve the crystals in water, which 

 may cause a slight error due to solubility, or to use the mixture 

 of equal parts water, acetic acid and alcohol recommended by 

 Classen.* When very little copper is present not more than 

 5 cm3 of nitric acid should be added before precipitation. With 

 amounts exceeding 50 mg. 10 cm3 should be used to 100 cmS of 

 liquid. A separation may be thus secured from 0*20 grm. of 

 cadmium. With 0*3 grm. of cadmium and 50 mg. of copper 

 it is possible to obtain satisfactory results when the volume on 

 precipitation is increased to 200 cm3 If 0*15 grm. of copper is 

 present, even under these conditions, some of the cadmium 

 comes down with the copper. Increasing the volume of nitric 



Table III. 

 Separation of Copper from Cadmium by Precipitation from a Solution Con- 

 taining a Large Amount of Acetic Acid. 





Cad- 



Volume 











• 



Copper 



mium 



at pre- 



Oxalic 



Acetic 



Nitric 



Copper 





present 



present 



cipitation 



acid 



acid 



acid 



found 



Error 



grm. 



grm. 



cm 3 



grm. 



cm 3 



cm 3 



grm. 



grm. 



0-0051 



o-io 



50 



1 



25 



5 



0-0052 



+ 0-0001 



0*0051 



o-io 



100 



2 



50 



5 



0-0045 



— 0-0006 



0-0051 



o-io 



100 



2 



50 



5 



0-0043 



— 0-0008 



0-0253 



0-20 



100 



2 



50 



10 



0-0251 



— 0-0002 



0-0511 



0-20 



100 



2 



50 



5 



0-0512 



+ 0-0001 



0-1533 



0-20 



100 



2 



50 



5 



0-1545 



+ 0-0012 



0*1533 



0-20 



100 



2 



50 



10 



0-1525 



— 0-0008 



0*0051 



0-20 



100 



4 



50 



5 



0-0049 



— 0-0002 



0-0255 



0*20 



100 



4 



50 



10 



0-0257 



+ 0-0002 



0-0510 



0-20 



100 



4 



50 



10 



0-0512 



+ 0-0002 



0-1530 



0-20 



120 



3'5 



50 



10 



0-1533 



+ 0-0003 



0-0051 



0-30 



100 



4 



50 



5 



0-0053 



+ 0-0002 



0-0511 



0-30 



100 



4 



50 



10 



0-0520 



+ 0-0009 



0-0511 



0-30 



200 



8 



100 



10 



0-0510 



-o-oooi 



0-1533 



0-30 



100 



4 



50 



10 



0*1556 



+ 0-0023 



0-1533 



0*30 



100 



4 



50 



20 



0-1556 



+ 0-0023 



0-1629 



0-30 



200 



8 



100 



10 



0-1643 



+ 0-0014 



0-1629 0-30 100 4 50 10 0*1636 



* Zeitschr. anal. Chem., xviii, 175. 



0-0007 



