31 



confounded with garnet, is known to be distinguished from 

 it by containing chrome, and by exhibiting, not the dodeca- 

 hedral, but the hexahedral form. The best analyses of it, 

 however, which are by Kobel and Wachtmiester, ai-e ob- 

 viously imperfect, of which no better proof can be given than 

 that Gustavus Rose, in his Crystallography, does not attempt 

 to give the formula of the mineral, but contents himself with 

 enumerating the different oxides of which it is composed. 

 Under these cii'cumstances. Dr. Apjohn conceived that a 

 re-examination of the constitution of pyrope would not be 

 without interest. He, therefore, undertook its analysis ; and 

 the result has been that he has detected in it yttria, one of 

 the rarest of the earths ; one, in fact, which had previously 

 been known to exist only in a few minerals of exceeding 

 scarcity. The yttria was insulated in the following manner. 



The mineral being fused with carbonate of potash, and 

 the silex separated in the usual way, the peroxide of iron, 

 alumina, and yttria were precipitated together by a mixed 

 solution of ammonia and sal-ammoniac. The alumina was 

 taken up by caustic potash ; and to the iron and yttria, dis- 

 solved in a minimum of muriatic acid, such a quantity of 

 tartaric acid was added, that upon subsequently pouring in 

 ammonia in excess there was no precipitate produced. The 

 iron was now removed by sulphuretted hydrogen; and the 

 solution evaporated to dryness, and ignited in a large pla- 

 tinum crucible, so as to volatilize the ammoniacal salts, and 

 burn away the carbon of the tartaric acid, left the yttria 

 slightly coloured by oxide of chrome. From this latter sub- 

 stance it is separated, but not perfectly, by the action of a 

 dilute acid, and by the addition of ammonia, or caustic potash, 

 to the solution the yttria is again recovered. That the sub- 

 stance thus obtained is yttria seems proved by the following- 

 considerations. 



It is separated, though not completely, from acids by 



