324 EARTHS PROPER, 



namely euclase ; the constituents of which, ac- 

 cording to the analysis of Berzelius, are as fol- 

 lows : 



Silica . 43-32 



Alumina . 30-56 



Glucina . 21-78 



Oxide of iron 2-22 



Oxide of tin 0-?0 



98-58 



Let us calculate the constitution of this min- 

 eral, on the supposition that it is composed of 

 two atoms silicate of alumina, one atom of sili- 

 cate of glucina, and a small quantity of bisilicate 

 of iron, probably accidentally present. 



(1.) 2-25 : 2 : : 3O56 : 27-164 = silica united to alumina. 

 (2.) 3-25 : 2 : : 21-78 : 13-403 = silica united to glucina. 

 (3.) 4-5 : 4 : : 2-22 : 1'973 = silica united to iron. 



Now, 27-164 + 13-403 + 1-973 =42-540, which 

 is less than the silica in the mineral by 0-98 grain. 

 Two thirds of the silica are united to the alumi- 

 na; consequently, only one third of 0'98 or 

 0-33 is to be added to the 13-403, making 

 13*733 grains for the silica united to the glucina. 

 Arid 



13-733 : 21-78 :: 2 : 3-1719 = atomic weight of glucina. 



From these two minerals we obtain two dif- 

 ferent atomic weights of glucina, the first too 

 high, and the second too low. The probability 



