A novel experimental method to determine the activity of alloy components in very dilute liquid metal solutions has been developed. The method is applied to the measurement of magnesium vapour pressure over nickel alloys to find the thermodynamic properties of magnesium in dilute liquid solutions at 1470°C. The experimental method employs a commercial Atomic Absorption Spectrophotometer to determine directly the vapour pressure of magnesium over the alloys. A radiatively heated Knudsen cell inside a vacuum system contains the metal. Equilibrium constants are given for the reactions, [Formula Omitted] where Al, 0 and Mg are dissolved in liquid nickel. Further, values for the metal-oxygen interaction coefficients [Formula Omitted] and [Formula Omitted] are determined. Finally, a value for the Raoultian activity coefficient at infinite dilution is suggested. A significant change in the activity of magnesium upon the addition of 20% chromium or iron to the dilute liquid nickel alloys was not detected. This is believed due to overpowering magnesium-oxygen interaction at these levels of chromium and iron. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate