Abstract: A system for measuring the quantity of hydrogen sulfide gas in a sulfur dioxide gaseous stream. A calorimeter is calibrated by a metered quantity of heated hydrogen sulfide calibration gas. A gas sample is grabbed from a source, generally a furnace, and a metered quantity is conditioned and introduced into a reaction cell. A probe in the reaction cell communicates with the calorimeter. The colorimeter measures the quantity of the hydrogen sulfide. A process logic controller monitors and operates the system and its internal and external components.