and on Yttria, Terbium and Erbium, 251 



amethyst colour which the salts generally present comes from 

 didymium, I will not, however, maintain. 



Addendum, July 1843. 

 Oti Yttria, Terbium and Erbiums 



I published last summer a short notice of yttria, concerning 

 which earth the following facts subsequently discovered merit 

 attention. When I stated on the former occasion that pure 

 yttria, as well as the salts of that base with a colourless acid, 

 are colourless, my experiments had only gone so far as to show 

 that all the yttria which I could procure for examination 

 might with ease be separated into two portions, the one a 

 stronger and colourless base, the other a weaker, which, in 

 proportion as it was free from yttria, acquired a more intense 

 yellow colour on being submitted to heat, and with acids gave 

 salts of a reddish colour. I continued my examination during 

 the following autumn and winter, and thereby was not only 

 enabled to confirm the correctness of my former observations, 

 but made the unexpected discovery that, as was the case with 

 oxide of cerium, what chemists have hitherto considered as 

 yttria, does not consist of one oxide only, but is for the most 

 part to be regarded as a mixture of at least three, of which 

 two appear to be new and hitherto unknown, all possessing 

 the greater number of their chemical characters in common, 

 for which reason chemists have so readily overlooked their 

 real differences. 



The characters which are peculiar to these oxides, and 

 distinguish them from all others are, — 1st, that although 

 powerful salt bases, all more so than glucina, they are inso- 

 luble in water and in caustic alkalies, but on the other hand 

 soluble, even after having been exposed to a strong heat, in a 

 boiling solution of carbonate of soda, although after a few 

 days the greater part separates from its solution in the form 

 of a double salt; 2ndly, that combined with carbonic acid, 

 they are largely soluble in a cold solution of carbonate of am- 

 monia, and that when such solution is saturated with them, a 

 double salt of carbonate of ammonia and the above carbonates 

 immediately begins to separate, and that in such quantity, 

 that after a few hours very little oxide remains in solution; 

 which explains the observations of several chemists, that, as 

 they express themselves, yttria sometimes dissolves freely, 

 sometimes scarcely at all, in carbonate of ammonia : further, 

 that the salts of these oxides have a sweet taste, and that the 

 sulphates dissolve with more difficulty in warm than in cold 

 water, without its following that they form double salts with 



