CHAPTER XII 



THE HALOGENS. 



A. FLUORINE. 



Fluorine. In 1813 and 1814 Davy published two papers 

 on " Fluor Spar " and the " Fluoric Compounds " ( Works, 

 V. 408424, 425 436). In these he recognised the 

 existence of an element, resembling chlorine, which he 

 proposed to call FLUORINE. The origin of these fluoric 

 compounds is described in his " Elements of Chemical 

 Philosophy" (1812), as follows : 



" There is a substance found abundantly in nature called 

 FLUOR SPAR ; it is usually either blue, green, yellow, or 

 white, transparent, and crystallised in cubes. It is a common 

 product of the mines in Derbyshire. 



" When this substance, in fine powder, is mixed with oil 

 of vitriol and distilled in retorts of silver or lead, connected 

 with receivers of the same metal artificially cooled, an 

 intensely active fluid is produced. It has the appearance 

 of sulphuric acid, but is much more volatile, and sends off 

 white fumes when exposed to air. It must be examined 

 with great caution, for when applied to the skin it instantly 

 disorganises it, and produces very painful wounds. When 

 potassium is introduced into it, it acts with intense energy 

 upon it, and produces hydrogen gas and a neutral salt : when 

 lime is made to act upon it, there is a violent heat produced, 

 water is given off, and the same substance as fluor spar is 

 produced. When it is dropped into water a hissing noise is 



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