Abstract
A recent study identified boron, sodium, aluminium and silicon as the dominant impurities in triple point of water (TPW) cells. These results suggest that borosilicate glass is a less than ideal container as it is the most likely source of the contaminating elements. An estimate for the rate of change of the equilibrium temperature of TPW cells is presented using results recently obtained at the National Research Council of Canada (NRC) and supplemented by those reported in 1982 by Furukawa and Bigge of the US National Institute of Standards and Technology (NIST). An analysis of the two data sets suggests that a decrease of 4 µK per year is appropriate in describing the average behaviour of TPW cells. The conclusion is speculative in that the behaviour of the various cells has not been monitored over a period of time to track the nature of the changes. Rather, the analysis assumes that the changes have occurred continuously and linearly with time.