186 ACIDIFIABLE COMBUSTIBLES. 



ide 5. If we reduce the weight of the manga- 

 nese in that proportion, the constituents of the 

 mineral become 



Silica. ... 48 



Protoxide of manganese 4<8 f 98 



Lime . . . 3-10* 



Magnesia . . . 0-22 



100'3 



Let us consider this mineral as a bisilicate of 

 manganese ; and let us calculate its composition, 

 on the supposition that an atom of silica is 2, 

 an atom of protoxide of manganese 4*5, an atom 

 of lime 3%5, and an atom of magnesia 2%5. 



(1.) 4-5 (atom of protoxide manganese) : 4 (2 atoms 

 silica) : : 48-98 : 43-53 = silica united to man- 

 ganese ....... 43-53 



(2.) 3-5 (atom lime) : 4 : : 3-1 : 3-54 = silica united 



to lime 3-54 



(3.) 2-5 (atom magnesia) : 4 : : 0-22 : 0-35 = silica 



united to magnesia .... 0-35 



Total silica united to the bases = 47'42 



This quantity of silica is 0*58 grain less than 

 what was found in the mineral by Berzelius. 

 The quantity which he found is Tauth part more 

 than it ought to have been, supposing an atom 

 of silica to weigh 2. Let us, therefore, deter- 



* Correcting Berzelius's estimate. 



