An azoxy compound can be treated with concentrated sulphuric acid to produce a nydroxyazo product consisting chiefly of the para isomer. This reaction, the Wallach rearrangement, is the basis for a suggested generic test for an azoxy compound. For the identification of a given azoxy compound, two derivatives are suggested: the hydrazo compound produced by the reduction of the azoxy compound by zinc dust, and the azo compound produced by the oxidation of the hydrazo compound. These compounds are described for the first time: 2,2′-dichloro-4-hydroxyazobenzene, 2,5′,2,5′-tetrachloro-4-hydroxyazobenzene, 2,2′-dimethoxy-5,5′-dichloroazobenzene, 3,3′,4,4′-tetrachlorohydrazobenzene, 2,2′-dimethyl-3,3′-dichlorohydrazobenzene, and 2,2′-dimethoxy-5,5′-dichlorohydrazo-benzene.