248 Professor Mosander on Cerium, Lanthanium, 



different means, but from the quantity of water of crystalliza- 

 tion, and other circumstances, the conclusion may be drawn 

 that the salt is really a double salt, although I cannot at pre- 

 sent say whether the other accompanying oxide is oxide of 

 lanthanium, or some other. That which I now thus briefly 

 describe as oxide of didymium is the basis in combination 

 with sulphuric acid in that salt whose properties I will now 

 communicate, as well as a method of obtaining it. The sul- 

 phate of oxide of didymium, prepared in different ways, 

 is much more soluble in water than the sulphate of oxide 

 of lanthanium. This circumstance induced me to try 

 whether by treating the mixture of the anhydrous salts in 

 great excess with water in small proportions, solutions could 

 not be obtained, which, in the order they had been procured, 

 should be richer in salts, and particularly in sulphate of oxide 

 of didymium, while, on the contrary, what remained undis- 

 solved, should be nearly pure sulphate of oxide of lantha- 

 nium; but after having examined five successive saturated 

 solutions, obtained from the same mixture of anhydrous 

 salts, it was found that one part of anhydrous salt had in the 

 first experiment been dissolved in 7*64 parts of water ; in the 

 2nd experiment in 8*48 parts ; in the 3rd experiment in 7*8 

 parts; in the 4th experiment in 5 parts, and in the 6th ex- 

 periment in 7*44 parts of water. These remarkable propor- 

 tions of salt dissolved I thus explained : during the dissimilar 

 degrees of temperature which accidentally arise under the 

 development of heat which takes place when, by the addition 

 of water to the anhydrous salt, this takes up water of crystal- 

 lization, salts containing unlike portions of water of crystalli- 

 zation, and of unlike solubility had been formed, and it was 

 for the purpose of ascertaining the correctness of this supposi- 

 tion that I afterwards prepared the solution of the salts in the 

 manner which I have already stated in describing the sul- 

 phate of oxide of lanthanium, the dissimilar solubility of which 

 salt with different degrees of heat was in this manner dis- 

 covered. If therefore the mixed salts, with a temperature 

 which should not exceed 48 c, 2 Fahr., be dissolved in G parts 

 of water, and the solution thus obtained afterwards heated to 

 104° Fahr., a quantity of light amethyst-coloured salt of lan- 

 thanium is deposited, which, by a repetition of the same treat- 

 ment, after ten to fifteen operations, becomes colourless and 

 nearly pure. The amethyst-coloured solution separated from 

 the salt of lanthanium is evaporated to dryness, and the salt is 

 freed from water; it is again dissolved in the before-mentioned 

 manner, but the solution is now heated to 122° Fahr., and 

 filtered after no more salt is deposited. The solution, now 



