Gas thermometer 4.58 torr Ice 273.16K Water Fig. 18-4 A triple-point ce which solid ice, liquid water, and water vapor coexist in thermal equi librium. By international agreement the temperature of this mixture has been defined to be 273.16 K. The bulb of a constant-volume gas ther mometer is shown inserted into th well of the cell4.58 torr 273.16 K