THORIUM. 



Glucina combines with sulphuric acid in several proportions, 

 forming a bisulphate (2 G 2 O 3 , SO 3 ), which is crystallizable, a 

 neutral sulphate (G 2 O 3 , 3SO 3 ), which may be obtained in solu- 

 tion, a soluble subsalt, G 2 O 3 , 2SO 3 , and an insoluble subsalt, 

 G 2 3 , S0 3 . 



Emerald or beryl is a silicate of the composition expressed 

 by G 2 O 3 , 4Si O 3 -h 2(A1 2 O 3 , 2Si O 3 ). This mineral crystallizes 

 in six-sided prisms, which are very hard. When coloured green 

 by oxide of chromium it forms the true emerald, and when co- 

 lourless and transparent aqua marina, which are both ranked 

 among the precious stones. The density of the emerald is 2.58 

 to 2.732. 



Euclase is also a silicate of glucina and alumina, G 2 O 3 , 2Si O 3 

 + 2(2A1 O 3 , Si O 3 ). It is a very rare mineral, which crystallizes 

 in limpid, greenish prisms. 



Chrysoberyl, one of the finest of the gems, consists essentially 

 of 1 atom of glucina combined with 6 atoms of alumina, G 2 O 3 , 

 6A1 2 3 . 



YTTRIUM. 

 Eg. 402.5 or 32.25 ; Y. 



The earth yttria was discovered in 1794, by Gadolin, in a 

 mineral from Ytterby in Sweden, which is now called gadolinite. 

 It has since been found in several other minerals, but all of 

 which are exceedingly rare. The metal was isolated from its 

 chloride by Wohler, precisely in the same manner as the two 

 preceding metals. It is of a darker colour than these metals, 

 and in oxidability resembles glucinum. 



Yttria is considered a protoxide, YO. Its density is even 

 greater than barytes, being 4.842. It is absolutely insoluble in 

 the caustic alkalies, is precipitated by yellow prussiate of po- 

 tash, and its sulphate and some others of its salts have an ame- 

 thystine tint, properties which distinguish it from the preceding 

 earths. 



THORIUM. 



Eg. 744.9 or 59.88 ; Th. 



This element was discovered by Berzelius, in 1824, in a 

 black mineral, like obsidian, since called t/write, from the coast 

 of the North Sea. This mineral contains 57 per cent of tho- 

 rina. This element has been named from the Scandinavian 



