The influence of some relevant metallic impurities in the triple point of mercury temperature

The influence of impurities on the defined fixed points of the International Temperature Scale of 1990 is one of the most relevant sources of uncertainty in their use. Namely, the triple point of mercury is one of the fixed points most used because its assigned triple point temperature (-39,8344 degrees C) is within a temperature range of high interest for science and industry. Mercury can be obtained with high purity, usually better that 8N and it is realized with a high accuracy, what makes impurities a significant contributor on the final uncertainty. The best procedure to quantify this influence is by means of doping experiments which consist of the addition of a controlled amount of an impurity, determined gravimetrically, in a fixed point cell. This paper presents a summary of the results obtained from a series of doping experiments performed with some relevant metallic impurities on the triple point of mercury temperature.