Our colleagues at the National Metrological Institute of Japan, Igor Maksimov and Toshiaki Asakai, have completed a set of Harned Cell measurements of HCl activities in HCl/TrisHCl solutions at different concentrations and temperatures. These data will be used to develop the chemical speciation model of Tris (2-Amino-2-hydroxymethyl-propane-1,3-diol, or THAM) buffers in seawater.They are the first of many sets of similar measurements that will be made in solutions containing Tris, TrisH+, Cl- and the inorganic components of seawater.