450 M. Berzelius on Fluoric Acid. [Dec. 



Article X. 



On Fluoric Acid, and its most remarkable Combinations. 

 By Jac. Berzelius. 



{Continued from p. 343.) 



II. Compounds of Fluoric Acid with Acids or Electronegative 



Oxides. 



The fluoric acid is distinguished from every other by its pro- 

 pensity to combine with the weaker acids in such a manner that 

 the latter act as bases ; and these compounds again unite with 

 the fluates of the electro-positive oxides, and form with them 

 double salts. These peculiar salts of fluoric acid and the electro- 

 negative oxides are farther characterised by this circumstance, 

 that, when in a similar degree of saturation, they are partially 

 decomposed by water ; an acid solution being formed, while the 

 negative oxide precipitates in an insoluble state, either uncom- 

 bined, or in union with a smaller quantity of fluoric acid. During 

 these decompositions, a portion of water combines with the 

 acid, and there is obtained in fact a double salt, in which water 

 acts the part of a base ; this water again may be displaced by 

 any of the more energetic bases, and a new double salt is 

 formed, in which both of the bases are metallic oxides. In all 

 cases where, after the decomposition of a neutral fluate by water, 

 an acid fluate remains in solution, we may remark in the latter 

 a strong tendency to form a double salt, by the substitution of a 

 different basis for the water. Perhaps a similar property may 

 be possessed by the neutral salts of other acids, which are in a 

 similar manner decomposed by water : it is not the case, how- 

 ever, with the salts of antimony and bismuth, from which water 

 produces an almost complete precipitation of the oxides. We 

 have long been aware that fluoric acid in union with silica forms 

 a distinct class of salts with the alkalies, such as potash and 

 barytes ; but the nature of these compounds has been hitherto 

 misunderstood. In what follows, I shall demonstrate, that 

 although characterised by peculiar properties, they are funda- 

 mentally analogous with the fluates of the saline bases. 



A. Fktate of Silica, or Silicated Fluoric Acid, and its Combina- 

 tions ivith the Saline Bases. 



The circumstance that silica and fluoric acid have been found 

 existing together in certain combinations, has caused them to be 

 regarded as constituting, while in that situation, a double acid, 

 capable of uniting with bases, and forming with them a class of 

 compounds to which I applied the provisional name of fluosili- 

 cates. In reality, however, this compound must be regarded as 

 a fluate of silica, for unless it undergo a previous decomposition, 



