THE VAPOR-PRESSURE OF CESIUM BETWEEN 370-DEGREES-C AND 660-DEGREES-C

We have measured the vapour pressure of caesium over the temperature r ange 370 degrees C to 660 degrees C using a pressure-controlled heat p ipe. The equation log(p/Pa)=a+b/T+c log(T/K)+dT+eT(2) with the coeffic ients a=34,573234, b=-4979,5799 K, c=-9,3234247, d=4,4733132x10(-3) K- 1 and e=-8,684092x10(-7) K-1 fits the data to within +/-8 mK over the entire range. In addition, the non-uniqueness of the ITS-90 appears to be less than +/-1,5 mK over the same temperature range based on the d ata from three thermometers.