ALUMINA. 301 



Silica ... 4-8 



Alumina . . 26-5 



Soda . . . 16-2 



Water . . . 9 -3 



100-0 



I analyzed a beautifully crystallized and pure 

 specimen, which I received from Mr. Heuland, 

 and found its composition almost identical with 

 the preceding analysis. 



Let us calculate the composition of this mine- 

 ral, on the supposition that it is a compound of 

 3 integral particles of silicate of alumina, and 1 

 integrant particle of trisilicate of soda, with 2 

 atoms of water. 



(1.) 2-25 : 2 : : 26'5 : 23-555 = silica united to alumina. 

 (2.) 4 : 6 : : 16-2 : 24-3 = silica united to soda. 



Now, 23-555 + 24-3 = 47*855, which is less 

 than the silica found in the mineral by O145 

 grain. One half of the silica being united to the 

 lime, it is obvious that, in order to have the true 

 quantity of silica united to the alumina in natro- 

 lite, we must add O07&5 to the 23-555 grains, 

 given by theory. And 



23-6275 : 25-7 : : 2 : 2-1 754 = atomic weight of alumina. 3.1754. 

 11. FELSPAR. 



Felspar consists essentially of silica, combined Felspar 



