Draeger-Tubes are glass vials filled w/ a chemical reagent that reacts to a specific chemical or family of chemicals. A calibrated 100 ml sample of air is drawn through the tube w/ the Draeger accuro bellows pump. If the targeted chemical(s) is present the reagent in the tube changes color and the length of the color change typically indicates the measured concentration. The Draeger-Tube Sysem is the worlds most popular form of gas detection.