Solubility measurements by in situ observation of the apex region formed by the (110), (11̄0) and (101) faces of tetragonal lysozyme crystals

► We measured Te by the apex observation of tetragonal lysozyme crystals (apex-observation method). ► We compared our Te to that of the step-observation on the crystal surface (step-observation method). ► The precision of Te, ΔH and ΔS in this study was comparable to that of the step-observation method. ► Our apex-observation method is easier and cheaper than step-observation methods.