'■'>'>-2 K. J. Roberts — Cerium by Potassium Permanganate. 



cerium is nearly all precipitated, the color is bleached more 

 slowly after each addition of the precipitant, and the efferves- 

 cence is less noticeable. The acidity of the liquid should now 

 be tested from time to time, which may be done with litmus 

 paper if only a slight excess of permanganate is present. Small 

 amounts of the mixed solution or of sodium carbonate are 

 added, until the liquid is nearly neutral to litmus, and still is 

 faintly colored with permanganate. The whole is heated and 

 stirred for about ten minutes, and filtered hot. The precipi- 

 tate is washed with boiling water till the washings give no 

 precipitate with ammonia. If the liquid at the end of the 

 precipitation is faintly acid, the filtrate usually contains a 

 trace of cerium giving a faint yellow color with ammonia and 

 hydrogen peroxide, while from the precipitate a preparation of 

 cerium chloride may readily be obtained which shows no 

 absorption bands in a thickness of 15 cm of very concentrated 

 solution. The presence of a little cerium in the filtrate, where 

 the earths in the latter are to be subjected to fractional crys- 

 tallization, is usually not objectionable. 



To insure the complete removal of the cerium, the liquid at 

 the end of the precipitation must be made absolutely neutral, 

 when a filtrate is obtained which gives no test for cerium with 

 hydrogen peroxide. Before testing, the excess of perman- 

 ganate is removed from the filtrate by boiling with a few 

 drops of alcohol. After re-filtering, the other earths are 

 precipitated by oxalic acid. The precipitate of cerium and 

 manganese hydroxides is dissolved in strong hydrochloric acid, 

 the solution diluted and precipitated with oxalic acid and the 

 cerium oxalate re-converted to nitrate. On repeating the pro- 

 cess with this materia], a pure cerium preparation is obtained, 

 which gives an oxide of the characteristic pale yellow color. 

 The process was thoroughly tested on several different kinds 

 of material. A mixture containing as much as thirty-five to 

 forty per cent of praseodymium and neodymium yielded pure 

 cerium in two operations. 



Attempts were also made to extract the first cerium and 

 manganese precipitate with dilute nitric acid, in order to 

 remove the last traces of praseodymium and neodymium 

 without recourse to a second permanganate treatment. The 

 precipitate obtained in the usual manner was thoroughly 

 washed on the filter, then transferred to a large dish and heated 

 nearly to boiling with a large volume of water. Nitric acid 

 was then added carefully until the liquid began to show the 

 permanganate color. The whole was heated for about fifteen 

 minutes, and the precipitate filtered off and washed. This 

 cerium preparation, when freed from manganese, gave a pale 

 reddish oxide, showing that the neodymium and praseodymium 

 are not entirely removed from the first precipitate by extrac- 

 tion with dilute nitric acid. 



