To determine co-efficient of expansion of a gas at constant pressure. A glass U-tube with a bulb and stopcock at one end, the other limb being open. An outlet tube from the bottom of the U tube passes through a rubber bung and has a stopcock at the end. The stem below the bulb is graduated 3 x 0.1 ml. An inlet tube with a mohr clip also passes through the bung. A glass water jacket encloses the U tube. All glass parts made of borosilicate glass requires only 20 ml mercury, which is not included.