A number of improvements in apparatus and technique have been made since the production of the prototype model of the controlled-clearance piston gage used by Johnson and Newhall in their 1953 determination of the freezing pressure of mercury at 0oC.
These improvements and the importance of this value have justified the redetermination report herein. The scope of modern high and ultra-high pressure research has indicated that known fixed points on the pressure scale need careful reestablishment. This experiment consists of placing a sample of mercury in a bomb which is then immersed in a constant-temperature (icc) hath and
subjected to increasing pressure. The pressure is continued until the mercury is observed to freeze, and in measuring this pressure by means of a free-piston gauge which is connected to the bomb.