GLUCTNA. 323 



Silica . 68-35 



Alumina . 17*60 



Glucina 13-13 



Oxide of iron 0-72 



Oxide of tantalum 0-27 



100-07 



Let us consider the emerald as a compound of 

 two atoms of trisilicate of alumina, and one atom 

 of trisilicate of glucina, and let us see what the 

 quantity of silica will be, supposing the atomic 

 weights of alumina and glucina to be 2-25 and 

 3-25 respectively. 



(1.) 2-25 (atom of alumina) : 6 (3 atoms silica) : : 17-6 

 (alumina in mineral) : 46-933 = silica united to alu- 

 mina. 



(2.) 3-25 (atom of glucina) : 6 : : 13-13 : 22-422 = silica 

 united to glucina. 



Now, 46-933 4- 22-422 = 69'355, which ex- 

 ceeds the silica in the mineral by 1 -005 grain. 

 The silica united to the alumina is very nearly 

 two- thirds of the whole ; consequently, two-thirds 

 of this surplus belongs to that portion of the 

 silica. There remain 0-335 grain, which must be 

 deducted from the 22-422. The remainder, 

 22-087, is the silica actually united to the glucina 

 in the mineral. Now, 22-087 : 13-13 : : 6 : 

 3-5668 = atom of glucina. 



2. EUCLASE. Composi . 



There is another mineral, containing glucina, 



X2 



