Precise pressure measurement in the range from 5 to 100 atmos. is quite a difficult problem. A set of high pressure mercury manometers is very unwieldy and difficult to use, while Bourdon gauges require frequent recalibration and are inherently inaccurate. The most likely solution for this problem is to use a simple piston‐in‐cylinder pressure balance, which, for these pressures and for accuracies of the order of 0.05 percent, can be relatively crude, and does not require excessively precise machining or care in use. A simple pressure balance was constructed for use in the pressure range from 25 to 35 atmos., and used for both pressure measurements and density change determinations. It proved perfectly satisfactory, giving pressures reproducible from day to day to about 0.01 atmos.