290 EARTHS PROPER. 



protoxide. Now, the atomic weight of protoxide 

 of manganese is 4-5, and of deutoxide 5. If we 

 reduce the manganese in the mineral in this pro- 

 portion, the quantity of protoxide will be 17 '244 

 grains. 



The peroxide of iron is probably foreign to 

 the constitution of the mineral, and may have 

 been introduced by percollation. 



Now, if we suppose every atom of alumina to 

 be united to an atom of silica, and every atom of 

 protoxide of manganese to be united to H atom 

 of silica, we shall obtain data for calculating the 

 constituents of the mineral. We shall consider 

 an atom of silica as 2, an atom of alumina as 

 2-25, and an atom of protoxide of manganese 

 as 4-5. 



(1.) 2-25 (atom of alumina) : 2 (atom of silica) : : 28-669 

 (alumina in the mineral) : 25-483 = silica united to 

 the alumina. 



(2.) 4-5 (atom of protoxide) : 3 (atom and half of silica) 

 : : 17-244 (protoxide in the mineral) : 11-496 = si- 

 lica united to the manganese. 



But 25-483 + 11-496 = 36-979, which exceeds 

 the whole silica found in the mineral by 0-825 

 grain ; but 3 1 2 of the silica is united to the man- 

 ganese : consequently, 0-257 of this excess 

 must be referred to that portion of the silica. 

 There remains 0-568, which must be subtracted 

 from the 25-483 grains of silica, given by theory 



