An atomic absorption spectrophotometer has been constructed to provide automated measurement of elemental vapor pressure changes with temperature. Three alloy‐containing absorption cells and a blank reference cell are fixed in a furnace which is automatically moved to position each cell sequentially on the spectrophotometer optic axis, while the furnace independently follows a predetermined time‐temperature profile. Measurements of spectral intensities and thermocouple outputs are recorded at selected intervals and are printed and punched on paper tape. Subsequent computer processing of the punched data yields values of thermodynamic activities and partial molar enthalpies and entropies of the alloy constituents.