Glass J-tube formed from 1 mm bore thick walled capillary tube, with a brass screw and collar at the end of the longer limb. A bubble of gas is introduced into the short limb. Used for sampling small quantities of gas held over water. This is then lowered into reagent solution and the bubble moved back and forth so that reagent diffuses through the end water seal. Use potassium hydroxide for CO2 or alkaline pyrogallol for O2. The change in length of the bubble indicates the amount of gas taken up by the reagent. Dimension: long limb - 250 mm and short limb - 100 mm.