The paper is a resume of work done by the author in 1949-1956 in connec- ion with nodular cast iron. The investigation was first performed in laboratory and since 1951 carried on in a number of foundries in production scale. Part of the compositions used is summarized and the C and Si are plotted as a graph. Among the factors which influence the mechanical properties, P content is the predominating one. Plotted in a plane, points denoting the tensile strengths and ductilities of irons of equal P contents lie more or less on a curve with shape near a hyperbola. The data show that using o,8% of 80-20 Cu-Ma alloy as the modifying agent for iron melted in a fire brick lined cupola, the tensile strength is 61-77 kg/mm2, and the ductility is 3-7% One test using 50-30-20 ferrosiliconnickel -magnesium as the modifying alloy yields as cast specimens with ductilities 18%, 8%, 14%, 16%. When Cu or Ni increases, the percentage of pearlite and the tensile strength increase while the percentage of ferrite and the ductility decrease. If the Cu and Ni contents are equal, the casting with Cu is some what stronger, and the casting with Ni is some what more ductile. The tensile streng- th of the quenched and tempered specimen may reach 144.1kg/mm2. The duc- tility of the annealed specimen may reach 2.3,5%. Experimental evidences led the author to the hypothesis that both the spheroidizing effect of Na to Al-Si alloys and the spheroidizing effect of Mg to cast irons are surface pbenomena. Na and Mg respectively form transient layers covering part of the surfaces of growing crystals of Si and graphite. The paper describes the preparation of Ma alloys, compares the efficiencies of different treating methods, and briefly narrates the numerous applications including preliminary trials with rolls and ingot molds. The paper is a resume of work done by the author 1949-1956 in connec- ion with nodular cast iron. The investigation was first performed in laboratory and since 1951 carried on in a number of foundries in production scale. Part of the compositions used Among the factors which influence the mechanical properties, P content is the predominating one. Plotted in a plane, points denoting the tensile strengths and ductilities of irons of equal P contents lie more or The data show that using o, 8% of 80-20 Cu-Ma alloy as the modifying agent for iron melted in a fire brick lined cupola, the tensile strength is 61-77 kg / mm2, and the ductility is 3-7% One test using 50-30-20 ferrosiliconnickel -magnesium as the modified alloy yields as cast specimens with ductilities 18%, 8%, 14%, 16%. When Cu or Ni increases, the percentage of pearlite and the tensile strength increase while the percen If the Cu and Ni contents are equal, the casting with Cu is some what what stronger, and the casting with Ni is some what more ductile. The tensile streng- th of the quenched and tempered specimen may reach 144.1kg / mm2. The duc-tility of the annealed specimen may reach 2.3,5%. Experimental evidences led the author to the hypothesis that both both the spheroidizing effect of Na to Al-Si alloys and the spheroidizing effect of Mg to cast irons are surface p benomena. Na and Mg respectively form transient layers covering part of the surfaces of growing crystals of Si and graphite. The paper describes the preparation of Ma alloys, comparable the efficiencies of different handling methods, and briefly narrates the numerous applications including preliminary trials with rolls and ingot molds.