122 M, ^erzelius on Silicium, [Aug. 



crystalline forms of bodies will require to be much farther 

 extended, before it will be possible to deduce unequivocal con- 

 clusions respecting the number of atoms of oxygen which exist 

 in oxides. The supposition that sihca is constituted of an atom 

 of each of its elements is unquestionably the simplest, and the 

 most convenient for the purpose of expressing the composition 

 of silicates by formulae ; but this view obliges us to admit the 

 improbable existence of silicates in which the silica contains six 

 times the oxygen of the base ; as, for example, in apophyllite, 

 in which one atom of potash would be combined with 12 atoms 

 of sihca. 



B. Fluohoric Acid, 



The characteristic properties of a strong and corrosive acid 

 which the compound hitherto styled fluoboric acid possesses, 

 have caused it, from our earliest knowledge of its existence, 

 to be regarded as a double acid, which, with bases, has a ten- 

 dency to form double salts, containing tivo acids and one base. 

 This property indeed it possesses in a far higher degree than 

 the silicated fluoric acid ; but, as is the case with that com- 

 pound, its most distinguishing tendency is likewise to produce 

 double salts containing one acid and tioo bases, the boracic 

 acid invariably constituting one of the latter. I shall hereafter 

 demonstrate that it thus forms a class of salts, which are con- 

 stituted in obedience to the same laws with the corresponding 

 salts of silica. 



Gay-Lussac and Thenard, and J. Davy, have stated, that 

 fluoboric acid is absorbed by water without decomposition. 

 This however is inaccurate ; for I have ascertained that when 

 the acid gas is passed into water, it deposits a considerable 

 quantity of boracic acid, just as siUcated fluoric acid deposits 

 one third of its silica. If the liquid acid be cooled or very 

 slowly evaporated, an additional quantity of boracic acid 

 separates; but if it be concentrated in an elevated temperature, 

 it volatilizes without leaving any residue, a proof that, in a 

 certain degree of concentration, the compound which had been 

 decomposed by water, is reproduced. 



It would be impossible by direct analytical experiments to 

 ascertain the composition of the gaseous fluoboric acid, or to 

 determine the quantity of boracic acid which is disengaged by 

 dissolving the gas in water, and indeed, without a previous 

 knowledge of silicated fluoric acid, the composition of fluoboric 

 acid, and the proportions of its combinations with other bodies, 

 would present two of the most diflticult problems which still 

 remain to be resolved by chemical analysis; but in conse- 

 quence of the complete analogy which subsists between the 

 properties of these two substances, the simplest experiments 

 suflice to demonstrate, that, with the exception of mere pro- 



