and Didymium. 245 



of a part of the salt immediately begins, and after that has 

 once begun the phenomenon continues even with so low a de- 

 gree of heat as 55°'1 to 57°*2 Fahr. less, until the solution 

 only contains y yths of its weight of anhydrous salt. The salt 

 which has thus been deposited contains the same quantity of 

 water as that which is formed during the evaporation, as well 

 under 55 0, 4 Fahr. as with 212° Fahr. If sulphate of oxide 

 of lanthanium be kept at a white heat for an hour, it loses the 

 half of its sulphuric acid, and the basic salt which is produced 

 is insoluble in water. 



Nitrate of oxide of lanthanium is a salt easily soluble in 

 water or alcohol, and from an evaporated solution of the con- 

 sistence of thin syrup, it crystallizes in large prismatic crystals, 

 which rapidly deliquesce in damp air. If the solution be evapo- 

 rated with a heat of 86° Fahr. and above, an opake milk-white 

 mass is obtained. If the salt be cautiously heated so that all the 

 water is expelled, then by care with a higher degree of tem- 

 perature, the anhydrous salt may be melted without decom- 

 position, and after cooling it resembles a colourless glass, but 

 with the least inattention respecting the temperature, a part 

 of the nitric acid is expelled, and the melted mass is a mix- 

 ture of neutral and basic salt, which stiffens to a snow-white 

 opake mass, which a moment after solidification has the re- 

 markable quality of falling asunder into a voluminous white 

 powder, with such violence, accompanied by a sort of slight 

 detonation, that parts of it are thrown about to the distance 

 of several inches. 



Oxide of lanthanium has a particular tendency to form basic 

 salts, and only such are precipitated with caustic ammonia ; 

 let this be added in as great an excess as may be, when also 

 it occurs that the combination with some organic acids, such 

 as tartaric acid, is dissolved in an excess of ammonia. Several 

 of the basic salts, for example, basic nitrate of oxide of lan- 

 thanium, and basic chloride of lanthanium, are marked by the 

 quality that they cannot be washed upon a filter with water, 

 which runs through of a milky colour, until no part of the 

 precipitate remains upon the filter, and if the liquid be boiled 

 with the precipitate which has been obtained, the whole runs 

 immediately through the filter. If the precipitate be allowed 

 to remain a few days wet upon the filter, it becomes changed 

 into a neutral salt which is dissolved in the water, and car- 

 bonate of oxide of lanthanium, which remains upon the filter. 



With regard to cerium, my investigations are as imperfect 

 in their results as those upon lanthanium ; I will, however, 

 make mention of some facts which may prove interesting for 

 the present. 



