246 Professor Mosander on Cerium, Lanthanium, 



The reddish-brown powder which remains after the extrac- 

 tion of oxide of lanthanium with dilute nitric acid, is a mix- 

 ture of the oxide of cerium with oxide of lanthanium, together 

 with all the above-named accompanying substances. I have 

 not been able to find any good method of obtaining pure 

 oxide of cerium ; the salts of protoxide of cerium are like those 

 of oxide of lanthanium, perfectly colourless, and with sulphate 

 of potash the protoxide of cerium is precipitated completely 

 from the solution. If hydrate of protoxide of cerium, preci- 

 pitated by caustic potash, be collected on a filter, it imme- 

 diately begins to grow yellow, and after the oxidation has 

 proceeded as much as possible in this manner in the air, there 

 remains after drying, opake light yellow lumps, which con- 

 tain water ; this being expelled by heat, leaves so-called oxide 

 of cerium, which has not the least trace of brown, but after 

 an hour's heating at a white heat, has a slight tinge of red. 

 If the oxide of cerium formed in the manner stated has the 

 slightest tinge of brown, or becomes dark after drying or heat- 

 ing, it proceeds from foreign substances. This yellow oxide, 

 however, always contains protoxide of cerium, and I have not 

 succeeded in obtaining oxide of cerium free from protoxide. 

 The bright yellow oxide which is formed when hydrate of 

 protoxide of cerium, either alone or mixed with hydrate of 

 oxide of lanthanium, &c, is exposed to the action of chlorine, 

 contains not only chlorine but even protoxide of cerium. If 

 nitrate of protoxide of cerium be heated, a light yellow 

 powder is obtained, from which much salt of protoxide of 

 cerium may be extracted with nitric acid, and if this solution 

 be again evaporated, and the dried mass heated, salt of prot- 

 oxide of cerium is again obtained, and this continues even 

 after the operation has been five times repeated. What I call 

 oxide of cerium is, therefore, really a combination of oxide of 

 cerium with protoxide. The ignited oxide of cerium is scarcely 

 affected by boiling concentrated muriatic acid, still less by 

 other weaker acids ; the hydrate, on the other hand, is easily 

 dissolved in muriatic acid, with the development of chlorine, 

 but even after a long boiling the solution retains a yellow 

 colour. Scarcely a trace of the hydrate of oxide of cerium is 

 dissolved by weaker diluted acids, but it assumes a darker 

 yellow colour, and combines with a portion of the acid em- 

 ployed. In the solutions of carbonated alkalies, particularly 

 carbonate of ammonia, the hydrate of oxide of cerium is 

 dissolved in large quantities, and the solution assumes a 

 bright yellow colour. Peroxide of cerium in solutions which 

 are heated to boiling, is immediately reduced by oxalic acid 

 to protoxide of cerium, while carbonic acid is developed. By 



