将肥皂溶解在乙醇溶液中，用已知过量的硫酸溶液中和游离碱，并用乙醇氢氧化钾溶液滴定过量的酸。如果肥皂含有添加剂（碱、硅酸盐、etw），则该方法不适用可按规定程序用硫酸分解。如果颜色干扰酚酞终点，则该方法也不适用于有色肥皂。

The soap is dissolved in an ethanolic solution, the free alkali is neutralized with a known excess of sulphuric acid solution and the excess acid is titrated with ethanolic potassium hydroxide solution. The method is not applicable if the soap cantains additives (alkali, silicates, etw.) which can be decomposed by sulphuric acid by the procedure specified. The method is also not applicable to coloured soaps if the colour interferes with the phenolphthalein end point.