Abstract: A test for determining the sulfur content of the base cast iron used for the production of nodular iron or iron containing compacted graphite. A sample of the molten base cast iron is removed from the melt, then a known amount of a nodular iron inoculant or a compacted iron inoculant is added to the molten metal. The molten metal sample is then cast into test bar or test wedge, solidified and tested to determine whether the bar or wedge is nodular iron or iron containing compacted graphite. The test may be fractured and inspected to visually determine whether the fracture is gray or white. Alternatively, the wedge or bar may be ultrasonically tested to determine whether the wedge or bar contains flake graphite or nodular graphite or compacted graphite. As a further alternative, the cooling or solidification curve of the molten metal sample, after inoculation, can be determined and compared with the cooling curve from a molten base cast iron sample.