A titration used to estimate amounts of reducing agents. The reducing agent being estimated is dissolved in concentrated hydrochloric acid and titrated with a solution of potassium iodate. A drop of tetrachloromethane is added to the solution. The end point of the titration is reached when the iodine colour disappears from this layer. This is due to the reducing agent being oxidized and the iodate being reduced to ICl. This reaction involves a four-electron change.