196 ACIDIFIABLE COMBUSTIBLES. 



silica, prepared in the way just described, was 

 left, unbroken, on the filter, for six weeks. Its 

 weight was 13-63 grains, Being exposed to a 

 red heat, it lost 5*13 grains ; consequently, the 

 anhydrous silica amounted to 8 '5 grains, and the 

 water to 5-13. Now, 8-5 : 5-13 : : 2 : 1-207 = 

 water united to 2 silica. This exceeds the atomic 

 proportion by about ftth of an atom, 

 ether 4 There are several other hydrates of silica, 



hydrates. 



besides the three which I have just described. 

 I have formed a hydrate, composed of 



3 atoms silica = 6 



1 atom water = 1-125 



7-125 



I have obtained another, composed of 



4 atoms silica = 8 

 3 atoms water = 3-375 



11-375 



This great variety of hydrates renders it always 

 indispensable in the chemical analysis of minerals 

 to expose the silica to a red heat, in order to be 

 sure of its true weight. 



Conciu- y The details in this section have been some- 

 what tedious ; but they were necessary to esta- 

 blish the true atomic weight of silica. Let us 

 recapitulate the different results obtained. 



sions. 



