SILICON. 191 



ble, I found that it had become lighter by 0*15 

 grain. Deducting this diminution, there remain 

 16%52 grains for the true quantity of carbonic 

 acid expelled. Now 16 '52 (the carbonic acid 

 expelled) : 12 (the silica employed) : : 2*75 (the 

 atomic weight of carbonic acid) : 1 '997^8 = the p ives 



/-.-.. 1 "99 *58 for 



weight of an atom of silica. the atom of 



From this experiment, which was several times S1 

 repeated, the atom of silica appears to weigh 

 1*99758, which is very nearly -nfooth part less 

 than 2 ; the atomic weight of silica, deduced 

 from the analysis of eight silicates, was a little 

 above 2. As the deviations in these two differ- 

 ent sets of experiments are on different sides, 

 there is a chance that the mean of the two may 

 come still nearer the truth. 



Atomic weight of silica from the analysis of eight 



silicates 2-00245 



Atomic weight of silica from heating silica and 



carbonate of potash .... 1-99758 



- Mean of 



Mean of both 2-00001 both gives 



2 O0001. 



This atomic weight is little more than ^^th 

 part greater than 2. 



IV. Silica enters into definite combinations 

 with water, forming various hydrates. Some of 

 these I have examined with care ; and they fur- 

 nish satisfactory evidence that the true atomic 

 weight of silica is 2. 



1. When silica is fused with potash or car- 



