SILICON. 187 



mine the atomic weight of silica, on the supposi- 

 tion that the constituents, as determined by 

 Berzelius, are rigidly accurate. 



The bisilicates of lime and magnesia may be 

 omitted as foreign bodies. They contain about 

 Ath of the whole silica ; consequently, yVth of 

 the surplus silica, or O05, must be subtracted. 

 The remainder is 0%53 : let us add this to the si- 

 lica united to the protoxide of manganese. This 

 gives us bisilicate of manganese composed of 



Silica . . . 44-06 or 4-04798 

 Protoxide of manganese 48-98 - 4-5 



Two atoms of silica weigh 4O4/798 ; consequent- Gives 

 ly, the weight of an atom will be 2-02399, which 

 exceeds 2 by rather more than 1 per cent. 



8. KNEBELITE, OR SILICATE OF IRON AND 

 MANGANESE. 



THIS ore has been described and analyzed by 

 Dobereiner. It is grey, with spots of various 

 colours, occurs in amorphous masses, and lias a 

 specific gravity of 3'714. According to Do- 

 bereiner's analysis its constituents are 



Silica . . . 32-5 

 Protoxide of iron . 32 

 Protoxide of manganese 35 



99-5 



