180 AC1DIFIABLE COMBUSTIBLES. 



Let us calculate the composition of hedenber- 

 gite, on the supposition that it is a trisilicate of 

 iron ; that silica weighs 2, and protoxide of iron 

 4*5. 



4-5 (atom of protoxide of iron) : 6 (3 atoms silica) : : 32-53 

 : 43-37 = silica united to the iron. 



The quantity of silica united to the iron (on the 

 supposition that an atom of it weighs 2) exceeds 

 the quantity in the mineral by 2*75 grains ; but, 

 in all probability, the oxide of manganese and 

 the alumina supplied the place of the deficient 

 silica. Now, 0*37 alumina will go as far in satu- 

 rating oxide of iron, as 0*328 of silica ; and 0*75 

 of protoxide of manganese will go as far as 0*333 

 of silica. We may, therefore, subtract 0*66 from 

 the deficient silica, thus reducing the deficiency 

 to 2'09 grains. 



If we suppose the analysis perfectly correct, 

 the composition of trisilicate of iron deduced 

 from it will be 



Silica . 41-28 or 5-7104 



Protoxide of iron 32-53 - 4-5 



According to this analysis, 3 atoms of silica 

 weigh 5*7104 : hence the atom of silica is ^f* 

 =19035. 



5. D10PTOSE, OR SESQUISILICATE OF COPPER. 



r phis mineral, which was at first confounded 



