276 PROCEEDINGS OF THE AMERICAN ACADEIMY 



the alkaline sulphates in place of the sulphate of luteocobalt. I have 

 also employed the sulphato-chloride of luteocobalt, Lcj (804)3012, as a 

 precijiitant, and find that double salts are sometimes formed which are 

 much more msoluble than those obtained with the sulphate, excepting 

 only in the cases of the four cerite earths. These contain chlorine as 

 well as sulphuric oxide, and they are sometimes at least formed when 

 sulphate of luteocobalt is added to a solution containing the chlorides 

 of metals of the cerium and yttrium groups. Sulphate of roseocobalt 

 gives in general the same result as sulphate of luteocobalt, only the 

 salts formed in this case are more soluble in both cold and hot water. 

 Experiments with the sulphates of xanthocobalt and croceocobalt 

 have not yet led to valuable results. Certain sulphates of the earths 

 appear to give with sulphate of luteocobalt only hydroxides of the 

 metals, R(0H)3. In this case it seems more probable that a true 

 double sulphate is at first formed and then decomposed, sulphuric acid 

 being set free. 



The following results may be of interest in this connection. A 

 portion of earths from Fergusonite sent me by Dr. Shai3leigh was 

 converted into sulphates; the cerite earths had been separated by sodic 

 sulphate, and the solution of the earths gave no further precipitate with 

 this. A solution of sulphate of luteocobalt gave no precipitate with 

 this solution in the cold, but on boiling a very abundant crystalline 

 precipitate, insoluble or very slightly soluble in boiling water. The 

 filtrate from these crystals gave only a small precipitate with ammonia, 

 so that the luteocobalt salt must have contained almost all the earths 

 other than the cerite earths. These are known to consist chiefly of 

 yttria. The crystalline precipitate obtained as above by boiling, and 

 insoluble in boiling water, dissolved completely in a large quantity of 

 cold water. The nitrates of roseocobalt and luteocobalt give, in 

 many cases at least, finely crystalline precipitates with the nitrates 

 of the earths. * In certain cases, white gelatinous precipitates of hy- 

 droxides are formed at the same time probably as in the case of 

 the sulphates above cited, in consequence of the formation of double 

 nitrates and their subsequent decomposition into free acid and hy- 

 droxide. This makes a new mode of differentiation which may prove 

 to be of use, and to which I shall return hereafter. As an instance I 

 may cite the case of the neutral nitrates of the gadolinite earths, from 

 which the cerite earths have been separated by sodic sulphate. A 

 strong solution of these nitrates gives with nitrate of roseocobalt, 

 Rc(N03)3, in a short time a bright orange highly crystalline and a 

 dirt}'^ white gelatinous precipitate. Both contain earths. The same is 



