376 M. Redtenbacher on Casium and Rubidium. 



and caesium, which depends on the solubility of the alums of 

 these three bases. 



All three alums are easily soluble in hot water ; but while 100 

 parts of water at 17° C. dissolve 13*5 of potash-alum, they dis- 

 solve 2*27 of rubidium-, and 0*619 of caesium-alum. Hence at 

 17°C. potash-alum is thirteen times, rubidium-alum fifteen times, 

 and caesium-alum eighty-eight times as soluble as the correspond- 

 ing platinum-salts. And while the solubility of the alums in 

 the different cases is as 



Potassium. 



22 : 



Rubidium. 



4 : 



Caesium. 



that of the platinum-salts is 







15 : 



2 : 



i. 



By this deportment a way is opened for the separation and 

 preparation of these metals on a large scale. 



Schiel describes* the following as a lecture experiment. A 

 test-tube containing peroxide of silver, drawn out in the middle 

 and sealed, is introduced into a well-dried stoppered gas-bottle, 

 which is then filled with chlorine. The flask being closed, the 

 tube is broken by shaking; the chlorine becomes paler, and 

 in a few minutes the flask is full of colourless oxygen gas. The 

 proportions of peroxide and chlorine must be those of their equi- 

 valents. The peroxide is readily prepared by passing ozonized 

 oxygen over dry oxide of silver. 



Poppf designates the following as the best of two methods 

 which he gives for separating oxide of cerium from the oxides of 

 lanthanum and didymium, with which it is usually associated. 

 The three oxides, dissolved in acid, are approximately neutralized 

 without producing a permanent precipitate. An adequate quan- 

 tity of acetate of soda is added and then an excess of hypo- 

 chlorite of soda, and the whole boiled for some time. The 

 cerium is deposited as a bright-yellow precipitate, the other bodies 

 remain in solution. The filtrate must not become turbid on 

 the addition of hypochlorite and boiling ; by careful and suffi- 

 cient addition of hypochlorite in the first case, one treatment is 

 sufficient, and every trace of cerium is precipitated free from lan- 

 thanum and didymium. 



The yellow precipitate contains much water; it dries to a 

 brownish-yellow, transparent and easily pulverizable. mass. It 

 has all the characters of a peroxide, and is doubtless CeO 2 . 

 it is formed in the same way as the peroxides of lead and manga. 



* Liebig's Annalen, December 1864. 

 t Ibid. September 1864. 



