Browning and Roberts — Separation of Cerium. 45 



Art. III. — On the Substitution of Bromine and of Iodine 

 for Chlorine in the Separation of Cerium from the other 

 Cerium Earths; by Philip E. Browning and Edwin J. 

 Roberts. 



[Contributions from the Kent Chemical Laboratory of Yale Univ. — ccvi.J 



One of the best known processes for the separation of 

 cerium from lanthanum and didymium is that of Mosander.* 

 This process consists in passing chlorine gas into a mixture of 

 the hydroxides suspended in a distinct excess of a fixed alkali 

 hydroxide, until the solution is saturated and the reaction of 

 the liquid is no longer alkaline to litmus. Under these con- 

 ditions nearly all the cerium remains undissolved as the eerie 

 hydroxide, while the other cerium earths go largely into 

 solution. In treating mixed material the residue of eerie 

 hydroxide generally retains some of the cerium earths so that 

 the treatment with chlorine must be repeated. Two disad- 

 vantages associated with this method therefore are, the prepa- 

 ration and use of chlorine gas, and the solvent action of the 

 hydrochloric acid formed in the reaction upon the eerie 

 hydroxide 



2Ce(OH) 3 + Cl 2 = 2Ce0 2 H-2HCl + 2H 2 0. 



The work to be described was undertaken to study the 

 effect of substituting bromine or iodine for chlorine in this 

 process. A preliminary experiment was made by suspending 

 a precipitate of the washed hydroxides of the cerium earths in 

 water, adding a little liquid bromine, and allowing the action 

 to go on for several hours with occasional stirring. The pre- 

 cipitate took on the color of the eerie hydroxide, and on filter- 

 ing the filtrate was found to contain a considerable amount of 

 cerium earths free from cerium. 



In the following experiments solutions of known amounts 

 of the mixed oxides, composed of about 50 per cent of cerium 

 and 50 per cent of the cerium earth oxides other than cerium, 

 were treated with a slight excess of sodium or potassium 

 hydroxide. To these hydroxides suspended in the alkaline 

 solution, liquid bromine or bromine water was added in dis- 

 tinct excess, and the mixture was placed upon a steam bath 

 until the greater part of the free bromine was expelled. The 

 residue was then filtered off, washed, and treated as before. 

 This process was repeated twice, and the filtrate after each 

 treatment was found to contain the amounts of cerium earth 

 oxides, free from cerium, indicated in the table. The residue 

 from the last treatment on being dissolved in acid showed only 



* J. prakt. Chem., xxx, 267. 



