Chemical elements
    Physical properties
    Chemical properties
      Boron Hydrides
      Boron trihydride
      Boron halogen
      Boron trifluoride
      Hydrofluoboric acid
      Potassium borofluoride
      Fluoboric acid
      Perfluoboric acid
      Boron subchloride
      Boron trichloride
      Boron tribromide
      Boron tri-iodide
      Oxides of Boron
      Tetraboron trioxide
      Boron dioxide
      Tetraboron pentoxide
      Boron sesqui-oxide
      Boron trioxide
      Boric anhydride
      Boric Acids
      Orthoboric acid
      Boric acid
      Boracic acid
      Complex Boric Acids
      Perboric Acid and Perborates
      Sodium perborate
      Sodium hyperborate
      Potassium perborate
      Rubidium perborate
      Ammonium perborate
      Barium perborate
      Boron sesquisulphide
      Boron trisulphide
      Boron pentasulphide
      Boron selenide
      Boron nitride
      Boron amide
      Boron imide
      Boron phosphide
      Boron phospho-iodides
      Boron carbide
      Boron thiocyanate
      Boron Alkyls
      Boron trimethyl
      Boron Silicides and

Fluoboric acid

When boron trifluoride in sufficiently large amount is passed into cold water, a colourless, syrupy liquid is produced. A similar liquid is obtained when as much boric acid as possible is dissolved in a cold, concentrated solution of hydrofluoric acid and the solution concentrated on the water-bath, boiled until it evolves white fumes, and cooled over concentrated sulphuric acid.

The liquid thus obtained, of density 1.584, has a composition in agreement with the formula H2B2O4.6HF. It is decomposed by excess of water with the precipitation of boric acid, an aqueous solution of hydrofluoboric acid being produced. Berzelius regarded the liquid as a definite acid, of which he could form the alkali salts M2B2O4.6MF.H2O by neutralisation with alkali. This view, however, is in all probability erroneous, although the evidence against the individuality of the liquid is not as conclusive as could be desired. Distillation of the liquid is accompanied by rise of boiling-point, and the successive liquid fractions differ in density and composition, whilst initially boron trifluoride is evolved. The " salts," when recrystallised, yield first MF and subsequently a mixture of MF and M2B2O4, while the "acid" in aqueous solution gives with silver nitrate a precipitate of silver metaborate mixed with silver oxide. According to Basarow, the liquid is merely a mixture of metaboric, hydrofluoboric, and hydrofluoric acids.

Two other fluoboric acids have been stated to exist, namely, H4B2O7.3HF and H4B2O9.2HF, but little is known concerning them. A physico-chemical study of mixtures of boric acid, hydrofluoric acid, and potassium fluoride has been made by Abegg; Fox, and Herz, but no definite conclusions could be deduced.

Although no fluoboric acids are definitely known, two compounds have been prepared which may be looked upon as salts of such acids. These are B2O3.2KF and KBO2.KF, to which the constitutions

have been assigned. The former is made by fusing 7 parts of boron sesqui- oxide with 12 parts of potassium fluoride, allowing the melt to cool slowly, and extracting soluble impurities with alcohol; the latter, by fusing the former with the requisite amount of potassium carbonate. The compounds dissolve without decomposition in a little water, but much water decomposes them.

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