286 Prof. Berzelius's Notice respecting Lantaniwn. 



cutting the sides, or the sides produced in D', E', F' : join 

 A D', B E', C F' : these lines all pass through a common 

 point v." Hence he deduces the following Cor. " Hence 

 by supposing D and D', E and E', F and F', to coincide, it 

 follows, that the three straight lines drawn from the 2 s, 

 to the points in which the sides touch the inscribed O pass 

 through the same point; and the same holds regarding the 

 points of conttict of any of the O's touching a side and the 

 continuations of the other two." 



Now a little consideration will show that this corollary 

 does not follow from the Prop. By supposing D and D', 

 E and E', F and F' to coincide, the original Prop, becomes 

 this : " If A D, B E, C F meet in a point, then will A D, 

 BE, C F, also meet in a point," which is a mere truism. 

 A D, B E, C F, do, in this case, certainly meet the points of 

 contact of the insc. O, and we know, from other sources, that 

 they meet in a point, but it is not so proved by this proposi- 

 tion. 



XLI. Notice respecting Lantanium. Extracted from a Let- 

 ter of Professor Berzelius to Professor Kersten of Frei- 

 berg* 



" T HEREWITH transmit to you the oxide of lantanium 

 -i- separated from the protocarbonate of cerium, which you 

 sent me. The oxide of lantanium was discovered in cerite, by 

 Mosander, about the end of last year. Lantanium occurs 

 everywhere with cerium, and [its oxide] has great external re- 

 semblance to the oxide of cerium, but is easily separated 

 from it, by dissolving the mixture of both in nitric acid, al- 

 lowing the solution to evaporate, and exposing the remainder 

 to a red heat. The oxide of cerium becomes by this process 

 almost absolutely insoluble in dilute acids, but the oxide of 

 lantanium dissolves easily, even in the most dilute acids, and 

 may be separated from the solution by carbonate of ammonia, 

 in which it is perfectly insoluble. It has very strong basic pro- 

 perties, and may be dissolved by digestion in solution of 

 muriate of ammonia. Its sulphate, like that of aluminum, is 

 less soluble in hot water than in cold, and is precipitated 

 entirely, while mixed with cerium, by sulphate of potash, but 

 only in part, when it is pure. It is easily distinguished from 

 it by its pale brick-red colour, and separated from it by its 

 ready solution in dilute acids. When heated in hydrogen 

 gas it becomes white, passing into green, without changing 

 its weight, and the salts thus formed have a greenish hue. 

 If heated in air, that is to say, in contact with oxygen, it is of 



• Communicated by Prof. Charles Kersten. 



