

E. J. Roberts — Cerium by Potassium Permanganate. 351 



3Ce(NO s ),+KMn0 4 + 3H,0 = 



2Ce(NO.,) 1 + Ce(OH) 4 + KNO a + H. J MnO ; ,. (1) 

 Tlie eerie nitrate formed then hydrolyzes: 



Ce(N0 3 ) 4 + 4H 2 0^ = kCe(bH 1 )+4HN0 3 . (2) 



If no alkali is added, the accumulation of nitric acid in the 

 liquid checks the process by reversing the action in equation 

 (2), and also in equation (1), for when a little of the mixed 

 precipitate of hyd rated eerie and manganese dioxides was 

 treated, after washing, with dilute nitric acid and warmed, a 

 strong permanganate color was produced. The addition of 

 alkali at this point of course simply removes the free acid and 

 allows the action to become complete. The fact that the 

 oxidation and precipitation take place even in the presence of 

 appreciable amounts of free nitric acid makes it possible to 

 secure a better separation than would otherwise be the case, 

 for if the liquid is kept perfectly neutral the small amounts of 

 trivalent earths which are locally thrown down by the alkaline 

 precipitating solution will not be re-dissolved, while if the 

 liquid is distinctly acid during the whole process they will tend 

 to re-dissolve on stirring. These considerations give the theo- 

 retical conditions for the process. As to the choice of a 

 neutralizing agent, it is of course desirable to use no compound 

 of a metal which is precipitated by oxalic acid or which is not 

 easily separated from the rare earths, as, for example, zinc 

 oxide or calcium carbonate. Magnesium oxide was tried, but 

 does not give as good results as the alkali carbonate, and is not 

 so easily controlled. Sodium carbonate seems to be the simplest 

 and most convenient neutralizing agent for the purpose. 



The solution used for the precipitation is made by dissolving 

 158 - 03 grams (one mol.) of potassium permanganate and 

 J-24'00 grams (four mols.) of dry sodium carbonate in any con- 

 venient amount of water. The solution should be kept in 

 glass-stoppered bottles and should not be allowed to come in 

 contact with organic matter. Solutions of pure permanganate 

 ami of pure sodium carbonate, of any convenient strength, are 

 also needed. The process is carried out as follows : The rare 

 earth solution, which should not contain other salts than 

 nitrates, is heated to boiling in a large porcelain dish, and, if 

 not already neutral, is neutralized with the sodium carbonate 

 solution. The solution of permanganate is added in small 

 quantities, until the red color just begins to be permanent, and 

 the mixed solution of permanganate and alkali is then added 

 very slowly, with constant stirring, the liquid being kept nearly 

 at the boiling point during the whole process. A faint color 

 of permanganate is maintained all the time in the liquid, a 

 little of the pure permanganate solution being added if at any 

 time the color is entirely bleached. This is important, as the 

 constant acidity of the liquid is thereby insured. When the 



