448 On the Native Sulphate of Iron and Alumina. [June, 



I repeated these experiments with a fresh quantity of the salt, 

 and the results agreed almost precisely with respect to the sul- 

 phuric acid and oxide of iron, but there was rather less alumina; 

 the difference was not, however, sufficient to induce me again to 

 repeat the analysis. 



I have stated on a former occasion my reasons for believing, 

 that hydrogen = 1, alumina is 27; and this determination is 

 strengthened by the results of Sir H. Davy's experiments stated 

 in p. 357 of his Elements, and to which 1 have only lately par- 

 ticularly adverted. He says that from experiments which he 

 " made on the quantity of ammonia required to decompose 

 saturated solutions of alumina in acids, it would appear that 

 the number representing alumina is about 48, and supposing it 

 to consist of one proportion of aluminum, and one of oxygen, 

 33 will be the number representing aluminum." If, however, 

 the atom of oxygen be represented by 8 instead of 15, then the 

 number for alumina will be, according to Sir H. Davy's experi- 

 ments, 25*6 ; now this sufficiently approaches 27 to assist in 

 deciding the question whether alumina should be represented 

 by 27, or by 18, which latter number Dr. Thomson considers to 

 be the weight of its atom. 



Representing then sulphuric acid by 40, protoxide of iron by 

 36, alumina by 27, and water by 9, it will appear that the sul- 

 phate of iron and alumina in question is composed of 



4 atoms of sulphuric acid . . 40 x 4 = 160 

 3 atoms of protoxide of iron 36 x 3 = 108 



1 atom of alumina = 27 



25 atoms of water 9 x 25 = 225 



520 

 We may then consider the salt as composed of 



3 atoms of sulphate of iron. 76 x 3 = 228 



1 atom of sulphate of alumina = 67 



25 atoms of water = 225 



Weight of the atom 520 



On this view of the subject, the theoretic composition of the 

 salt will be as follows, which, it will be observed, agrees very 

 nearly with the analysis : 



Sulphuric acid 30*76 



Protoxide of iron 20*76 



Alumina 5*19 



Water 43*26 



Loss 0*03 



100*00 



