and Properties of Silickm. 265 



residuum heated to redness. Treating tliis with water, it still 

 gave a little silica, which, after the addition of a drop of am- 

 monia, took at the expiration of some hours a colour inclining 

 to a yellowish-brown : when heated to redness it weighed 1 '5 ; 

 it had lost its dark colour, but it was not snow-white. With 

 soda it gave on platinum foil a faint but evident trace of 

 manganese. 100 pai'ts of silicium had consequently absorbed 

 105*25 of oxygen, and produced 20525 of silica. The experi- 

 ment was repeated on a portion of silicium on which fluoric 

 acid had been evaporated, in order to be more certain that all 

 the silica had been removed. 100 parts of silicium, previously 

 calcined to redness in the air, gave, by the process described 

 above, 207 of silica ; and by evaporation of the waters, 1 part ; 

 or in all, 208 of silica. 



According to these two experiments, silica is composed of 



Silicium 48-72 to 48*08 



Oxygen . . . . 51-28 to 51-92 



They both give a greater proportion of oxygen than that 

 which I found, according to the capacity of saturation of silica 

 for saline bases, and which is only 50"3. 



But if we return to the analysis of the salts containing fluate 

 of silica, we shall be able to calculate the saturating capacity 

 of silicium according to the results which we have obtained 

 from it. 



Of all these double salts, that of barytes is the most suitable. 

 The only uncertainty which could be met with in its analysis 

 arises from its retaining a little humidity which is not disen- 

 gaged until the moment of its decomposition. But the quan- 

 tity of it may be determined by melting the salt with oxide of 

 lead ; for the acid is retained, and the water only disengaged. 

 100 parts of the salt lost in this manner 0-85 of moisture. 

 100 parts of the same salt, weighed at the same time, gave, 

 according to the process described for the analysis of the 

 fluate of silica and barytes, 82-933 of sulphate of barytes, re- 

 presenting 54-428 of barytes. But according to the analysis 

 already known of the double fluate of silica and barytes, the 

 base is combined with three times more fluoric acid than in 

 the neutral fluate. It thence follows that the double salt is 



formed of Barytes 54-428 



Fluoric acid , . 22-836 



Silica 21-886 



Moisture .... 0-850 



100-000 

 Tlie 54-428 parts of barytes are saturated by 7*612 of 

 fluoric acid; whence it follows that 15-224 of this acid were 

 Vol. 65. No. 324. April 1825. L 1 combined 



