Abstract: An antimicrobial composition which comprises an isothiazolone compound, suppresses decomposition of the isothiazolone compound and reduces irritation of skin caused by the isothiazolone compound is provided. The antimicrobial composition comprises an isothiazolone compound of the following formula [1] or formula [2] and an aminocarboxylic acid of the following formula [3] or a derivative thereof: wherein R1 is hydrogen, alkyl, alkenyl, alkynyl or aralkyl; X and Y are each hydrogen, halogen or form a benzene ring with the carbon atoms at the 4- and 5-positions of the isothiazolone compound; M is a cation of an alkali metal, alkaline earth metal, heavy metal or amine; Z is an anion; a is 1 or 2; n is an integer; R2 is hydrogen or alkyl; R3 is C1-C5 alkylene; R4 is hydrogen or C1-C5 alkyl; R2 and R4 form a heterocyclic group; and b is 0 or 1.

Abstract: An agent for preventing scale formation and a method for preventing scale formation include a polymer which has at least 50% of N-vinyl formamide units or N-vinyl acetamide units and a phosphorus compound added to water in a cooling water system, a boiler water system, or the like. The scale preventing agent and scale preventing method of the present invention are effective in preventing the adherence of various types of scales which are generated in cooling water systems, boiler water systems, and the like. In particular, the present invention is effective in preventing the adherence of silica and calcium scale.