The present invention relates to a method for producing compacted graphite cast iron using a thermal analysis step, where a) one or two sample vessels, where the inner surface is partially coated with a material, which will lower the concentration of dissolved elementary magnesium, and partially coated with a relatively inert coating; and b) at least three temperature responsive means, of which at least one is arranged in the centre of the vessel/vessels, at least one is placed close to the coating affecting the level of dissolved elementary magnesium, and at least one is situated close to the relatively inert coating, are used.