Though the benzophenone method of synthesis is not quite advantageous for dalbergin and methyl dalbergin, it is more convenient for the preparation of allo-dalbergin (4-phenyl-5-methoxy-6-hydroxy coumarin) and its methyl ether. These compounds and other 4-phenyl coumarins give markedly coloured solutions when treated with alcohol, hydrochloric acid and magnesium; a number of 4-methyl coumarin derivatives also give similar colour reactions. On the other hand 3-phenyl and 3-phenyl-4-methyl coumarin derivatives do not respond to this test which may therefore be of diagnostic value.