400 FLUORINE. 



the gas forms tubes of silica, in the water, through which it 

 gains the surface without decomposition, if they are not broken 

 from time to time. When water is completely saturated with 

 the fluoride of silicon, it has taken up about once and a half its 

 weight, and is a gelatinous, semi-transparent mass, which fumes 

 in the air. The liquid contains two equivalents of water to one 

 of the original fluoride of silicon ; but one third of the fluoride 

 has been decomposed by the water and converted into hydro- 

 fluoric acid and silica. The hydrofluoric acid and fluoride of 

 silicon, in solution, are supposed to be in combination by Ber- 

 zelius, forming 3HF + 2Si F 3 , which is termed by him hydro- 

 fluosilicic acid. When this liquid is placed in a moderately 

 warm situation, the whole of it gradually evaporates, the free 

 hydrofluoric acid reacting upon the deposited silica, with forma- 

 tion of water ; and fluoride of silicon is revived. 



The most remarkable property of the fluoride of silicon is to 

 produce, with neutral salts of potash, soda and lithia, precipi- 

 tates which are gelatinous, and so transparent, as to be scarcely 

 visible at first in the liquor, and with salts of bary tes, a white and 

 crystalline precipitate, which appears in a few seconds. Almost 

 all the basic metallic oxides decompose this acid, when they are 

 employed in excess ; separating silica, and giving rise to metallic 

 fluorides. When, on the other hand, no more of the base is 

 applied than the quantity required to neutralize the free hydro- 

 fluoric acid, combinations are obtained with all bases, which are 

 analogous to double salts; consisting of a metallic fluoride com- 

 bined with fluoride of silicon, the proportion of the latter con- 

 taining twice as much fluorine as the former. The formula of 

 one of these compounds, the double fluoride of silicon and po- 

 tassium, is 2SiF 3 + 3KF, and those of other metals are similar. 

 The ratio of 2 to 3, in the equivalents of the two fluorides which 

 form these double salts, is unusual. 



Dr. Clark, to whose judgment on the subject of atomic 

 weights I would greatly defer, considers that the equivalent 

 number of silicon adopted by Berzelius is too high by one third; 

 and should be reduced from 277-31 to 184.8/. With this 

 change, silica comes to consist of 1 eq. of silicon and 2 of oxy- 

 gen, or is analogous to carbonic acid ; and the fluoride of silicon, 

 of 1 of silicon and 2 of fluorine. The double fluorides, in ques- 

 tion, may then be represented by single equivalents of fluoride of 

 silicon and metallic fluoride ; fluoride of silicon and potassium, 



