304 EARTHS PROPER. 



Silica . 68-46 



Alumina . 19-30 



Soda . 9-12 



Lime . 0-68 



Oxide of iron O28 



97-84* 



Let us suppose the bases combined with silicon 

 in^the state of trisilicates, and let us calculate 

 the composition on that supposition from Rose's 

 analysis. 



(1.) 2-25 : 6 : : 19-3 : 51-466 = silica united to alumina. 

 (2.) 4 : 6 : : 9-12 : 13-68 = silica united to soda. 

 (3.) 3-5:6:: 0-68 : 1-165 = silica united to lime. 

 (4.) 4-5:6:: 0-28 : 0-373 = silica united to protoxide of 



iron. 



Now, 51-466 + 13-68 + 1-165 + 0-373 = 66-684, 

 which is less than the silica in the mineral by 

 1-776 grain. It is not improbable that, if the 

 loss, amounting to rather more than two per 

 cent,, and which was more likely to fall upon the 

 bases than the silica, had not taken place, this 

 excess of silica would not have occurred in our 

 calculation. But let us see what the atomic 

 weight of alumina will be, supposing the analy- 

 sis accurate. 



The silica united to the soda, lime, and oxide 

 of iron is 2 -fr part of the whole ; and 2 -fr part 

 of 1 '77^ = 0-655, which being taken from 1 -776 



* Gilbert's Annalen, LXXIII. 18C. 

 9 



