and Didymium. 243 



Some of the results which I obtained unfortunately became 

 known to the public. When we find the oxide of a body hi- 

 therto unknown, nothing, generally speaking, is easier than the 

 determination of the qualities of the body, and I therefore ex- 

 pected to be able to give a complete account of my experiments 

 in a very short time, but on this point I was much deceived. 

 That which, in the first place, gives any value to chemical in- 

 vestigation, is the certainty that the object investigated is pure, 

 that is to say, free from foreign substances. 1 had not made 

 much progress in the details of my inquiry, when it appeared 

 that what I at first considered to be pure oxide of lanthanium, 

 was, in point of fact, a mixture of the new oxide with a num- 

 ber of other substances, so that in the course of the experi- 

 ments I succeeded in separating no less than seven different 

 substances, one after the other. The first, to my great sur- 

 prise, was lime, in no considerable quantity; and I have found 

 that sulphate of lime and sulphate of potash forms a double 

 salt sparingly soluble. Afterwards the following oxides were 

 successively separated, and by the application of different 

 means, namely, oxide of iron in large quantities, of copper, 

 tin, nickel, cerium, and something resembling uranium, &c. ; 

 but even the oxide which remained after the separation of all 

 these substances, left me in nearly the same position which I held 

 at the commencement of the researches, so that, although at 

 the end of the year 1839 I had already been fortunate enough 

 to obtain oxide of lanthanium tolerably pure, it was not until 

 the beginning of the following year that I was able, with any 

 facility, to obtain a larger quantity of it; but, notwithstanding 

 all my efforts, I have not yet succeeded in discovering any 

 method of separating, with any degree of analytical accuracy, 

 lanthanium from cerium, &c. 



Oxide of lanthanium, as pure as I have hitherto been able 

 to obtain it, possesses the following properties : — It is of a 

 light salmon colour, or nearly white, but not in the least red- 

 dish or brown, and retains its appearance unchanged when 

 heated either in open or close vessels at a red or white heat : 

 the slight colour seems to proceed from a small remnant of 

 some foreign substance. The oxide, although just previously 

 ignited to a white heat, soon changes its appearance in water, 

 becomes snow-white, more bulky, and after twenty-four hours 

 in the ordinary temperature of the air, becomes changed to a 

 hydrate easily suspended in water. With boiling water this 

 change takes place very quickly, and begins immediately ; the 

 newly heated oxide as well as the hydrate immediately restores 

 the blue colour to moist reddened litmus paper. Oxide of lan- 

 thanium is easily dissolved by acids even much diluted. Salts, 



R2 



