ALUMINA. 287 



water, and forms a variety of hydrates ; a precise 

 analysis of which will also throw considerable 

 light upon the atomic weight of alumina. Let 

 us see what number we shall obtain for the ato- 

 mic weight of alumina, deduced in each of these 

 ways. 



I. The number of minerals containing alumina 



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as an essential constituent is very considerable, sitkm of 

 The acid substance with which it is most com- m 

 monly combined is silica. It occurs, indeed, 

 combined with phosphoric acid, fluoric acid, and 

 mellitic acid ; but the mode of analyzing such 

 combinations is still too imperfect to render it 

 safe for us to trust to them for determining a 

 point of such importance. Beryl would be an 

 excellent mineral for our purpose, were it not 

 that the atomic weight of glucina has not been 

 yet determined with sufficient precision to al- 

 low us to employ it in investigating the atomic 

 weight of alumina. I shall, therefore, satisfy 

 myself with the following mineral species, all of 

 which have been analyzed with much care, and 

 in a state of as great purity as possible ; but I 

 have investigated the atomic weight of alumina 

 from a much greater number of species, and 

 have obtained very nearly the same result as from 

 the species which we are going to examine. 



