 The ferric chloride test is a traditional colorimetric test for phenols , which uses a 1 % iron ( III ) chloride solution that has been neutralised with sodium hydroxide until a slight precipitate of FeO ( OH ) is formed . The mixture is filtered before use . The organic substance is dissolved in water , methanol or ethanol , then the neutralised iron ( III ) chloride solution is added — a transient or permanent coloration ( usually purple , green or blue ) indicates the presence of a phenol or enol . 
