534 Prof. It. Bunsen's Spectral- Analyticul Researches. 



The precipitate was washed with acidified water, dissolved iu 

 a slight excess of dilute sulphuric acid, and the solution repre- 

 ^ipitated by pouring into a litre of boiling water. The solution, 

 precipitation, and washing were repeated two or three times 

 before every impurity was removed from the precipitate. After 

 these processes the greater part of the cerium remains in solu- 

 tion, so that but a few grammes of the pure cerium compound 

 are obtained from 100 grammes of the mixed oxides. 



A pure product may be obtained from the various liquids 

 collected during the processes by treating them as described 

 above. 



The perfect purity of the substance thus obtained was shown 

 by the following behaviour : — 



The pale-yellow hydrated oxide precipitated by caustic potash 

 from the solution of the basic sulphate, when treated with 

 chlorine in a concentrated solution of caustic potash, yielded a 

 deep orange-red oxidation product, without the solution (although 

 saturated with chlorine) taking up the smallest trace of a foreign 

 earth. Cerium oxide, after being strongly heated in the air, is 

 of a pure yellowish white colour, which changes to orange while 

 the oxide is hot. The sulphate does not give the smallest 

 precipitate (thorium oxide) when warmed with sodium dithio- 

 nate. The oxalate is to a considerable extent soluble in am- 

 monium oxalate solution, but is entirely reprecipitated on dilu- 

 tion with cold water. Small quantities obtained in this way by 

 fractional precipitation, when converted into chlorides, showed 

 one and the same spark-spectra when examined, and gave no 

 indication of the lines peculiar to lanthanum or yttrium. No 

 appearance of the absorption- spectra of didymium or erbium 

 could be obtained with any of the concentrated cerium solu- 

 tions. 



In Pltae V. no. 13 e, is shown the spark-spectrum obtained 

 with the chloride of this pure cerium material ; the most impor- 

 tant lines, which are not,, however, very characteristic, are 

 situated at 68, 71, and 79. The preparation of pure lanthanum 

 compounds is best commenced with the liquid from which basic 

 cerium sulphate has been for the first time precipitated by 

 means of boiling acidified water. This liquid is boiled with 

 natural pulverized magnesite, whereby the greater part of the 

 dissolved cerium oxide is precipitated. After removing the 

 precipitate, oxalic acid is added to the liquid acidified with 

 hydrochloric acid; the precipitate which is formed is strongly 

 heated in a porcelain crucible till the oxalic acid is decomposed ; 

 the oxides thus formed are dissolved in sulpphuric acid ; the 

 solution is evaporated, diluted with water, and again boiled with 

 magnesite. The liquid, which yet contains traces of cerium, is 



