252 Professor Mosander on Yttria, 



sulphate of potash, which are insoluble in a saturated solution 

 of the latter. 



If the name of yttria be reserved for the strongest of these 

 bases, and the next in order receives the name of oxide of 

 terbium, while the weakest be called oxide of erbium, we 

 find the following characteristic differences distinguishing the 

 three substances: — The nitrate of yttria is extremely deli- 

 quescent, so much so that if a small portion of a solution of 

 that salt be left for weeks in a warm place, the salt produced 

 will not be free from humidity. The solution of nitrate of 

 oxide of terbium, which is of a pale reddish colour, soon eva- 

 porates, leaving a radiated crystalline mass, which does not 

 change in air unless it be very damp. The crystals of sul- 

 phate of yttria are colourless, and remain clear and transparent 

 for weeks in air at a temperature varying from 86° Fahr. to 

 158° Fahr., while a solution of sulphate of oxide of terbium 

 yields by evaporation, at a low temperature, a salt which im- 

 mediately effloresces to a white powder. Oxide of terbium, the 

 salts of which are of a reddish colour, appears, when pure, to 

 be devoid of colour, like yttria. Oxide of erbium differs from 

 the two former in its property of becoming of a dark orange 

 yellow colour when heated in contact with air, which colour 

 it is again deprived of, with a trifling loss of weight, by heating 

 it in hydrogen gas ; and it is to the presence of oxide of erbium 

 that yttria owes its yellow colour, when prepared as hitherto 

 directed : and it is moreover probable, that in all those cases 

 where a colourless yttria has been supposed to have been ob- 

 tained, the presumed yttria has consisted for the most part 

 of glucina, at least before it was known how to separate the 

 last earth completely. 



The sulphate and nitrate of the oxide of erbium are devoid 

 of colour, although the solution of the oxide in acids is some- 

 times yellow, and the sulphate does not effloresce. 



These and a number of other less remarkable differences 

 between the three oxides, appear to me to place beyond a doubt 

 that what we have hitherto obtained and described as yttria, 

 is neither more nor less than a mixture of these three bases, 

 at least such is the case with yttria prepared from gadolinite, 

 cerine, cerite, and orthite, but as I have not yet had the good 

 fortune to discover any tolerably easy or certain mode of ob- 

 taining the one or the other oxide chemically pure, I shall 

 confine myself for the present to this short statement of facts. 



I proceed to make known two easy methods by which che- 

 mists may prove the correctness of the above statements. 

 If caustic ammonia in small quantities at a time be added to 

 a solution of ordinary yttria in muriatic acid, and the preci- 



