On Wed, 6 Mar 2002, Joseph B. Reid wrote: > ... 237.l6 K for the triple point of water was experimentally > determined, and just possibly in the future another digit might > be added to the above constant.
True, Joe, there was much experimental history leading to the value 273.16 K for the triple point of water, but that value is now set more or less permanently to define the kelvin scale. There are nine isotopic variations of water molecules, and each has its own unique triple point which can be differentiated on the present kelvin scale. The single "fixed point" of the kelvin scale (at 273.16 K) is realized in laboratories by observing a "natural" mix of the isotopes as found in sea water which has been purified by removal of dissolved salts, gases, and other impurities. It is possible that the triple point of only one of the nine isotopic variations of water will be selected in the future as the single triple point used to define the kelvin scale, but that is a remote possibility. Gene.
