Terbium and Erbium. 253 



pitate following each addition be washed and dried apart, we 

 obtain basic salts, of which the last precipitated are colourless, 

 and contain yttria only. Going backwards in reverse order from 

 these last, we find the precipitates becoming nearly transpa- 

 rent, reddish, and containing more and more oxide of terbium, 

 while the first precipitates contain the greatest proportion of 

 oxide of erbium, mixed with oxide of terbium and yttria. If 

 a solution of ordinary yttria in nitric acid be treated in the 

 same manner, and the several precipitates be heated sepa- 

 rately, the first precipitate will give a dark yellow oxide, the 

 colour of each succeeding one will be paler and paler, till at 

 last a white oxide will be obtained, consisting chiefly of yttria, 

 with a trifling quantity of oxide of terbium. In making these 

 experiments it is of importance that the yttria be free from 

 iron, uranium, &c, a matter of considerable difficulty. It is 

 therefore better to commence precipitating with a weak solu- 

 tion of hydrosulphuret of ammonia, and when the precipitate 

 has no longer a shade of bluish green, then to apply the caustic 

 ammonia as described. A better method in general is to add 

 a portion of free acid to a solution of yttria, and then to drop 

 in a solution of binoxalate of potash, continually stirring till 

 the precipitate no longer redissolves. In a couple of hours a 

 precipitate will form, which is to be separated, and the re- 

 maining solution treated as above described, and that as long 

 as any precipitate is formed. If the remaining fluid be then 

 neutralized with an alkali, a small quantity of nearly pure 

 oxalate of yttria is obtained. Of the precipitates the first ob- 

 tained are most crystalline, and fall quickly, the last more 

 pulverulent, sinking slowly. The former contain most oxide 

 of erbium, mixed with oxide of terbium and yttria; the next 

 contain less oxide of erbium, more of terbium and yttria ; while 

 the latter contain more and more yttria, mixed with oxide of 

 terbium. The first precipitates are always reddish, and the 

 last colourless. If a mixture of the oxalates of these bases 

 be treated with a very diluted acid, we obtain first a salt con- 

 taining mostly yttria, then one richer in oxide of terbium, and 

 the remainder contains principally oxide of erbium. I have 

 even once succeeded in obtaining a double salt of sulphate of 

 potash and sulphate of oxide of erbium (which is with difficulty 

 dissolved in a saturated solution of sulphate of potash), by 

 treating a somewhat concentrated solution of the nitrates of 

 oxide of terbium and erbium with an excess of sulphate of 

 potash. 



That much time and labour have been employed in arriving 

 even at the results which I have hitherto obtained, will be 

 evident from the little I have been enabled to make known, 



