ALUMINA. 295 



Silica 



Alumina 



Lime 



Potash with some soda 



Protoxide of iron 



Protoxide of manganese 



Water 



100-000 



The variation in the proportion of alkali and ox- 

 ide of iron is equally conspicuous in this analysis. 

 Let us calculate the constitution of the mineral 

 on the former supposition. 



(1.) 2-25 : 2 :: 31-97 : 28-417 = silica united to alumina. 

 (2.) 3-5:2:: 23-856 : 13-632 = silica united to lime. 



But 28-417 + 13-632 = 42-049, which exceeds 

 the quantity of silica present in the mineral by 

 2-134 grains. 



The silica united to the lime is ~tli of the 

 whole. Now j^th of 2-134 = 0-69 ; and 2-134 

 0-69 = 1-444, which must be subtracted from 

 the 28-417, leaving 26-973- And 



26-973 : 31-97 : : 2 : 2-3705 == atomic weight of alumina. 



We have obtained three different atomic 

 weights of alumina, namely, 



1. From Gmelin's analysis . . . 2-1960 



2. From Stromeyer's analysis of Monte Somma 



meionite 2-3841 



From ditto of Tyrol meionite . . 2-3705 



3 ) 6-9506 



Gives 



Mean 2-3168 2-3168. 



