An apparatus for measuring the reduced inorganic sulfur content of a sample. The apparatus has a reaction chamber (12) and means (14) for introducing a reducing agent that can selectively convert the reduced inorganic sulfur of a sample in the reaction chamber (12) to hydrogen sulfide. The reducing agent can be chromous chloride. The apparatus also includes means for measuring the amount of hydrogen sulfide evolved by reaction of the reducing agent with the sample and a detector for detecting when evolution of the hydrogen sulfide has reduced or ceased. The term "reduced inorganic sulfur" refers to sulfur in a form that can undergo oxidation and includes mineral sulphides and elemental sulfur.