244 Professor Mosander on Cerium, Lanthanium, 



when they are formed by the combination of the oxide of lan- 

 thanium with uncoloured acids, are absolutely colourless, as 

 well as the most concentrated solutions of the same. Salts of 

 lanthanium have a sweet, slightly astringent taste, and the 

 solution of them can be completely separated from oxide of 

 lanthanium by the addition of sulphate of potash in sufficient 

 quantity, because the double salt formed by sulphate of oxide 

 of lanthanium and sulphate of potash is quite insoluble in a 

 solution saturated with sulphate of potash. The atomic weight 

 of oxide of lanthanium, as it has hitherto appeared in most 

 instances, has oscillated about 680, a number which, however, 

 possesses no scientific value, when, as I have already remarked, 

 an absolutely pure oxide has not yet been obtained. 



Of the salts produced, I will only briefly describe a few of 

 the most characteristic. Sulphate of oxide of lanthanium cry- 

 stallizes in small six-sided prisms terminated by six-sided 

 pyramids, containing three atoms of water of crystallization. 

 This salt has the same property as sulphate of yttria, thorina, 

 and other oxides of the same class, namely, being much less 

 soluble in warm than in cold water. At 73°*4 Fahr. one part 

 of anhydrous sulphate of oxide of lanthanium requires 42^ 

 parts of water to be dissolved, but of boiling water one part 

 of the same salt requires about 1 15 parts. 



The crystals are very slowly dissolved, but the anhydrous 

 salt is immediately dissolved. The anhydrous salt developes 

 much heat when mixed with a little cold water, and the salt 

 then forms a crystalline crust, which afterwards is very slowly 

 dissolved. If powdered sulphate of oxide of lanthanium be 

 thrown into water whose temperature is 35°'6 or 37 0, 4 Fahr., 

 and kept stirring, and with the" precaution that the liquid, 

 which besides should be cooled from the outside, never attains 

 a higher temperature than 55 0, 4 Fahr., one part of sulphate 

 of oxide of lanthanium maybe dissolved in less than six parts 

 of water, and the solution preserved unchanged for weeks, in 

 closed vessels, and within the stated limits of temperature ; 

 but if the liquid be gradually heated, then before the tem- 

 perature has reached 86° Fahr., a number of crystalline 

 groups composed of small needles radiating from a common 

 centre begin to deposit, and when once this crystallization has 

 commenced it cannot be checked, however rapidly we may 

 cool the liquid. With regard to the number and form of 

 the deposited groups, the originally clear liquid is changed in 

 a few minutes to a thin pap. If during the dissolution of the 

 salt according to the manner stated, a part of the liquid 

 acquires a higher temperature through the heat that is deve- 

 loped by the union of the salt with water, the crystallization 



