Gas purity tester is an absorption bottle designed to eliminate confusing cocks, hose connections, awkward manipulation and usual caustic spillage. It consists of caustic reservoir and calibrated absorption burette mounted to a PVC polished frame. The reservoir and burette are held to the frame with two neoprene covered mounting bands that are adjustable from the rear side of the frame. The caustic reservoir has a line indicating the level to which caustic solution should be added, which volume is slightly in excess of the capacity of the absorption burette. The line drawings are used for identification of the purity tester parts.