The equilibration of the collected gas was observed experimentally by using the tank as a constant-volume gas thermometer
. After the tank valve was closed, the pressure of the collected gas was monitored, as shown in Fig.
The largest is 1000 [cm.sup.3] for the interpolating constant-volume gas thermometer (ICVGT).
The capability for performing calibrations of thermometers in the cryogenic range (i.e., T < 120 K) has been maintained at NBS/NIST since 1939 starting with the National Bureau of Standards Constant-Volume Gas Thermometer Scale of 1939 (NBS-39 Scale) (29).