Abstract: A gas testing apparatus of the type that directs a stream of gas to be tested through a tube containing reagent chemicals. The apparatus has a connector fitting to enable it to be connected to a closed system containing the gas to be tested, a base member having an orifice that reduces the pressure of the gas delivered to the testing tube to near atmospheric, a sliding cover that encloses the testing tube when it is positioned in the holder, and a rising stem indicator that indicates that gas flow has commenced through the tube. The apparatus also has tube seat seals for insuring that all gas entering the apparatus must flow through and not bypass the testing tube.