The standard Gibbs energy changes of the following reactions have been measured by using transpiration method; The standard Gibbs energies of the formation of 4CaO·P2O5 (ΔG°f,(4CaO·P2O5)) and 3CaO·P2O5 (ΔG°f,(3CaO·P2O5)) have been derived as follows; The reasons for discrepancies from reported values were discussed from the view point of whether the activity of phosphorus is measured directly or not.
