pH of Solutions of Potassium Hydrogen d-Tartrate from 0° to 60°C

Al t hough it is impossible to est ablish a t hermodynami c scale of hydrogen-io n a ctivi ty, Ug, t he N BS pH stand ards are assigned pH values that approa ch as closely as possible log U R in dilute b uffer solutions. In order to avoid t he un cer tainti es of t he liquid jun ction, electromotive-fo rce measurements of hydrogen-s ilver chloride cells lVithou t liquid jun ction were used to obtain the s tandard pH. To assign pH values t o four standa rd tar t rate buffer soluti ons in the temperat ure ran ge 0° to 60° C, electromotive-fo rce da ta were obtained for 30 aqueous mi xtures of potassium hydroge n tartrate and sodium chloride. One of t he proposed standards is a sa turated solution of po tassium hydrogen tar t ra te at 25° (pH 3.56) , and t he others are 0.03-, 0.02-, and O.OI-molar wi t h respect to t hi s sa lt . DirecLions for t he prepa rat ion a nd preservation of tart rate buffer standa rds are give n.