A characteristic blue or green colour reaction with concentrated nitric acid is given by the fully alkylated ethers of resorcinol and phloroglucinol and by a number of carbonyl derivatives of them. n the case of these carbonyl compounds one orthohydroxyl could be free. Certain flavanone derivatives of phloroglucinol also give this test whereas chalkones, flavones, diketons and coumaranones do not. It is useful for the differentiation and characterisation of closely related and isomeric compounds belonging to the above categories.