Hydrofluorio acid

On a manufacturing scale, an aq. soln. of hydrofluorio acid is made by gently heating the best quality of powdered fluorspar, free from silioa, to about 130° along with cono. sulphuric acid—containing 10 per cent, of water. The retort is a cast-iron pot with a cast-iron cover. The rim of the cover dips into an annular trough the joint is sealed with cone, sulphuric acid. The retorts are connected with a series of lead boxes as condensers. These contain water or dil. hydrofluorio acid to absorb the gas from the retorts. The condensers are submerged in water to keep them cool, and the acid so obtained is collected in leaden bottles. 

If it is desired to employ fluoborlc acid HBF it can be prepared by adding 100 g. of A.R. boric acid in small proportions to 325 g. of A.R. hydrofluoric acid (40 per cent. HF) cooled in ice the hydrofluoric acid is contained in a Bakelite beaker, a beaker coated with wax or in a lead vessel. A simple container may also be prepared by cutting off the neck of the wax bottle (in which the hydrofluorio acid is supplied) with a large (e.g., a butcher s ) knife which has been slightly warmed. One-third of the above solution should be employed in the preparation. Handle with great care. 

Amnio FetUaftwride is not known in the free state. Marignao obtained a double conq>ound A8F,4-KT in colourless crystals by dissolving potasdum arsenate in hydrofluorio acid. 

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