fluoric acid

Since fluorine must always be negative relative to oxygen, oxyacids analogous to those of the other halogens cannot be expected (24). Almost certainly, perfluoric acid HFO₄, or fluoric acid HFO₃, or hypofluorous acid HOF, will not therefore be prepared.

1959, American Rocket Society, “Jet Propulsion”, in ARS Journal, volume 29, American Rocket Society, page 96

Pure fluoric acid causes a flocculent precipitate in barytic water, which an excess of the same acid or of the nitric or muriatic acids, will redissolve. […] Fluoric acid diluted with six or seven parts of water dissolves zinc rapidly, and with disengagement of much hydrogen. The solution at first remains clear owing to the excess of acid, but after a time the fluat of zinc separates almost totally in white flocculi. The same salt is made immediately by adding fluat of potash to sulphat of zinc. This fluat is tasteless, insoluble in water, but readily dissolves in nitric, muriatic, or its own acid. It cannot be crystallized. The habitudes of iron with fluoric acid much resemble those of zinc, only the fluat of iron is much less easily soluble in an excess of its own acid. Fluoric acid moderately concentrated, does not act upon metallic tin cold or hot, but it readily dissolves the peroxyd of this metal. This salt may be evaporated to dryness without being sublimed, in which it differs from the muriat of tin.

1807, Arthur Aikin, Charles Rochemont Aikin, “Alkaline and Earthy Fluats”, in A Dictionary of Chemistry and Mineralogy , with an Account of the Processes Employed in Many of the Most Important Chemical Manufactures: To which are Added a Description of Chemical Apparatus, and Various Useful Tables of Weights and Measures, Chemical Instruments, &c. &c. Illustrated with Fifteen Engravings, volume 1, London, England: John and Arthur Arch, page 104