Abstract: A polyazo dye represented by the formula ##SPC1##Wherein A is an aromatic ring having or not having a substituent, B is an aromatic ring having at least one substituent selected from the group consisting of amino, substituted amino and hydroxyl, Y is hydrogen, alkali metal, --NH.sub.4 or an amine salt residue, n is 1 or 2, and each of R.sup.1 and R.sup.2 is hydroxyl or amino, R.sup.1 being amino when R.sup.2 is hydroxyl and hydroxyl when R.sup.2 is amino. The polyazo dye has outstanding utility in the dyeing of fibers having hydroxyl and/or amide groups and are not carcinogenic.

Abstract: Copper and copper alloys are prevented from rust by surface-treating the copper and copper alloys with at least one compound selected from the class consisting of alkylimidazoles represented by the following formula: ##SPC1##Wherein R is a long straight chain alkyl group of 5-21 carbon atoms and R' is hydrogen atom or a lower alkyl group, and their acid addition salts. The compound is used as it is, or in a solution, by dipping, spraying, coating or directly contacting with copper or copper alloy. The surface -treated copper and copper alloy can well withstand tarnishing in an atmosphere containing sulfur compound gas.