FLUORINE (ante). Fluorine has a strong tendency to form double fluorides: those containing hydrogen have acid reactions, as hydrofluosilicie acid, 211F,SiF.; hydroboro fluoric acid, This tendency to form double salts has suggested the idea that fluorine is diatomic, and that its equivalent should be 3S instead of 19. On this hypothesis,which, however, is not generally accepted, hydrofluoric acid could be instead of IIF., Hvdrofluosilicic acid, or silicofluoric, or fluosilicic acid, is formed by the action of water do fluoride of silicon (q.v.). The reaction may be represented as follows: 3SiF,--1- = A special apparatus is required on account of the tendency of the gelatinous silicic acid, one of the results of the decomposition, to stop up the tube which delivers the gaseous fluoride of silicon. This stoppage takes place when the tube is moist. By sinking it beneath the surface of mercury which underlies the water, the difficulty is obviated. When the bubble of gas escapes from the mercury and rises above the water, that part of the silica which has not escaped forms a sort of envelope, and a continuous tube of silica is often formed. The acid solution
is cleared by passing it through linen, ordinary filtration being impracticable, as tire filter is liable to become clogged. A. modification of the process has been introduced by Tessie Du Motay, which has an important relation to arts and manufactures. A paste composed of alumina, fluor-spar, carbon and silica is baked into bricks, which, on being melted again in a furnace, become decomposed, the fluoride of silicon passes off, and leaves a residuum in thefurnace. The gaseous fluoride of silicon is passed through a series of wooden chambers in which sprays of water are arranged to play upon sloping shelves of glass. The acid solution is carried by gravity fromone chamber to another until it contains about 8 per cent of acid. It is a sour fuming liquid which does not ordinarily corrode glass. When evaporated in glass, however, decomposition takes and the hydrofluoric acid which remains combines with the glass. Hydrofluo silicic acid is used in testing for barium and potassium. It is proposed to use it in pre paring various salts from the potassium chloride beds at Stftssfurt, Germany.