Fluoric acid

[…] that this is not hypofluorous acid but fluoric acid, HFO₃. Thus the behaviour of these fluorides supports the view that the reaction of halides with water takes place through an intermediate co-ordination compound; […]

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.

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.

On the other hand, Sir H. Davy contended that fluoric acid, in its strongest form, is anhydrous; for, on combining it with ammoniacal gas, a dry fluate of ammonia is formed, from which no water can be expelled by heat. He maintained, also, that fluoric acid is composed, not of an infammable base and oxygen, but of hydrogen united with a negative electric body, analogous to chlorine, to which he has given the name of fluorine. According to this view, when the metal potassium is brought into contact with fluoric acid, the hydrogen is not derived from water, but from the acid, and the supposed fluate of potash is a compound of fluorine and potassium. The phenomena are explained with the same ease by either theory, although the arguments upon which they depend are thought, by the majority of chemists, to preponderate in favour of the view proposed by Sir [Humphry] Davy. Fluoric acid forms salts by uniting with several bases. Five fluates have hitherto been found native; viz., the fluate of lime, or fluor-spar, the fluo-silicate of alumine, or topaz, the fluate of cerium, the double fluate of cerium and yttria, and the double fluate of soda and alumine, or cryolite. The four latter are very rare minerals, but the first is abundant. Potash unites with fluoric acid in two proportions, forming a fluate and a bifluate, the former of which consists of one atom and the latter of two atoms of acid united with one atom of the alkali. A neutral fluate of soda may be obtained directly from fluoric acid and carbonate of soda. It melts with more difficulty than glass; 100 parts of water, at 212° Fahrenheit, dissolve only 4.3 of it.