250 Professor Mosander on Lanthanium and Didymium, 



salt by means of the blowpipe, the bead becomes amethyst- 

 coloured with great tendency to violet, exactly as with a trace 

 of titanic acid after reduction. 



Oxide of didymium heated upon platina foil with carbonate 

 of soda, melts to a gray-white mass. With regard to the salts 

 of didymium, I shall briefly describe those which are ana- 

 logous to the before-mentioned salts of lanthanium and cerium, 

 and must at the same time mention that the basic salt of 

 didymium which is precipitated by caustic ammonia, can be 

 washed without passing through the filter. 



The mode in which sulphate of oxide of didymium is ob- 

 tained, as well as its appearance, has been already stated; this 

 salt is readily soluble in water at the ordinary temperature of 

 the air, although the crystals are very slowly dissolved. The 

 anhydrous salt is at once dissolved, if before the solution it is 

 not suffered to combine with water of crystallization. Should 

 this occur in such a manner that the anhydrous salt is covered 

 over (qfver gjutes) with a little water, the mass becomes heated, 

 and a hard salt crust is formed, which must be reduced to 

 powder before it can be quickly dissolved. At the ordinary 

 temperature of the air, one part of anhydrous sulphate of 

 oxide of didymium requires five parts of water for solution. 

 This solution begins at 127 0, 4- Fahr. to deposit crystals, the 

 number of which increases in the same degree as the tempera- 

 ture increases, so that the boiled solution contains only one 

 part of anhydrous salt to 50 \5 parts of water ; at a low red heat 

 an inconsiderable quantity of sulphuric acid goes off, but after 

 an hour's exposure to a white heat, the salt loses two-thirds 

 of its acid. With sulphate of potash, sulphate of oxide of di- 

 dymium gives an amethyst- coloured double salt, which is com- 

 pletely insoluble in a saturated solution of sulphate of potash. 



Nitrate of oxide of didymium is very soluble in water, cry- 

 stallizes with difficulty; the solution evaporated to thin syrup, 

 has a beautiful red colour, which seen in a certain direction 

 approaches blue. If the salt be evaporated to dryness in a 

 warm place, and heated to melting, which cannot be effected 

 without a great portion of the nitric acid being decomposed, 

 a red fluid is obtained, which, cooled and solidified, does not 

 fall to powder with violence, like the corresponding salt of 

 lanthanium, but retains its form. 



I must not omit to mention on this occasion, that amongst 

 the many other bodies which in the course of these researches 

 I was obliged to examine, yttria also presented itself, and I 

 have found that this earth, free from foreign substances, is per- 

 fectly colourless, and gives perfectly colourless salts : that the 



