S-Benzylthiuronium chloride reacts with ethylene glycol, derived from hydrolysis of the fluorides, to produce a crystalline substances. Using this, the fluorides can be indentified by measuring melting point. And when the zirconium-alizarin solution reacts with ethylenefluoro hydrin or ${eta}-fluoroethyl$ acetate, the red-violet color disappears to produce a yellow dye, which exhibits absorption maximum at about $530;m{mu}$ using the 250-microgram standard. Using these properties, the fluorine compounds can be determined conveniently by this method.