1826'.]' M, Set'xelius on Stlicium, 121 



of barytes, equivalent to 54-428 parts of barytes. Now, I have 

 already proved that in the double siUcated fluates, the base is 

 associated vy'ith thrice as much acid as in the neutral salt. Con- 

 sequently, the silicated fluate of barytes which I analyzed was 

 composed of 



Barytes 54-428 



Fluoric acid 22-836 



Silica 21-886 .. 



Moisture 0-850 ^; 



100-000 -^'^* 



These 54*428 parts of barytes were saturated by 7-612 parts 

 of fluoric acid ; the remaining 15*224 parts of this acid had been 

 therefore combined with 21*886 parts of silica ; or the fluate of 

 silica is composed of 



Fluoric acid . ...... 41-024 100 



Silica... 58*976 143-76 



But 100 parts of fluoric acid imply the existence of 74*7194 parts 

 of oxygen in the base by which it is saturated. Consequently^ 

 this quantity of oxygen must be contained by 143*76 parts of 

 silica, and silica must be composed of ^j; 



Silicium 48-025 100 



Oxygen 51*975 ...... 108*22 



This number corresponds very closely with that of the last 

 synthetical experiment. If we suppose silica to contain three 

 atoms of oxygen, the atomic number of silicium will be, accord- 

 ing to the above analysis = 277*2, and according to the synthe- 

 tical experiment = 277*8. 



This number exceeds by If per cent, the number which has 

 been hitherto adopted, and which corresponds so well with the 

 most exact and the most recently performed analyses of pure 

 minerals, that the present one, if made the basis of the calcula- 

 tion, would necessarily indicate in them an excess of sihca : I 

 must here mention, however, that we rarely find a mineral to 

 whose constitution sihca is even altogether foreign, v^hich does 

 not contain it to the amount of from one-half to upwards of two 

 per cent, in the state either of quartz or of some other sihceous 

 mineral ; and this mechanical intermixture of silica is still more 

 likely to exist in those minerals in which it constitutes at the 

 same time an essential ingredient. 



The number of atoms of oxygen contained by silica is still left 

 undecided by the foregoing experiments. The circumstance 

 that its carburet does not alter in v/eight when calcined affords 

 indeed a presumption that silica belongs to the class of oxides 

 which contain three atoms of oxygen ; but our knowledge of the 



