The method for killing bacteria, fungi and algae comprising applying to materials vulnerable thereto an effective amount of one or more compounds of the formula ##STR48## where X represents hydrogen atom, chlorine atom, bromine atom, methyl group or nitro group, Y represents hydrogen atom, methyl group, an alkylcarbonyl group where the alkyl group has from 1 to 12 carbon atoms, and may be substituted by one or more halogen atoms, a lower alkoxy carbonyl group, a lower alkylamino carbonyl group or a metal atom of which the valence is 1 or 2, Z represents hydrogen atom or chlorine atom and n represents 2 when Y represents a divalent metal and n represents 1 when Y does not represent a divalent metal.