THE RARE EARTHS. MAGEE. Ixvii 



same trouble, too, is one of the chief reasons for the appearance on several 

 occasions of pseudo elements which, obtained with extreme difficulty, 

 seemed to have a fair claim to separate existence, and which required 

 considerable time and skill to prove their non-existence. 



Let me illustrate. You are all aware that in the case of our ordin- 

 ary elements there are sharp points of separation. HC1. throws down 

 from a, silver salt solution all (or nearly all, for this reservation must be 

 made in the light of refined methods) the silver as AgCl. H a S throws 

 -down from solution a large number of sulphides even in acid solution we 

 must grant, but for every one of these elements there is some known 

 reagent or some exact method of treatment, which affects one and obly 

 one cf these elements. There are, undoubtedly, difficulties in exact 

 separations, but a fair analytical chemist can always separate them. 

 With the rare eaiths, however, each reagent seems to act so similarly that 

 there is no sharp line of demarcation, and the only methods applicable to 

 their separation are slow and remarkably difficult of application. Abso- 

 lutely quantitative analytical processes are unknown, and no results 

 published in the various mineralogical books as giving the composition of 

 the minerals containing them are reliable. I put forward no claims to 

 superiority as an analytical chemist, but I was occupied from October 1st 

 to the Christmas vacation, with all the advantages of a well equipped 

 laboratory at my disposal, in obtaining 11 grams of pure Ceria, using a 

 method proclaimed as the best to date, but acknowledged to need, as my 

 experience also confirms, a seven times repetition to ensure so-called 

 purity, and- leaving behind the suspicion that, as it was purified according 

 to the standard of a vanishing test, it was even then not absolutely pure. 

 Yet this subject has received some of the best thought of the ablest 

 chemists of the world during the past 50 years. Bahr, Bunsen, Earnmels- 

 burg, Wolf, Wing, Gibbs, Wbhler, Popp, Crookes, Marignac, Delafon- 

 taine, Boisbaudran, Nilson, Cleve, Kruss, Bettendorf, Welsbach, in fact 

 all the advanced inorganic chemists of the past half century. There is 

 no discouragement, the fight goes on with that grim deteimination to 

 succeed which only the scientist knows. What have they accomplished 

 for the world 1 Not much in this line ! But if these were all the 

 scientist strove for, our discoveries and advance would be of a low order. 

 Indirectly, the close study and wide experience with reagents and 

 methods has led to many useful results, but we need not linger over this. 

 Throughout all the period during which Ni. an Co. have been known, 

 there was no ready and direct method of separating them \ but a few 



