水中硬度系指沉淀肥皂的程度，使肥皂沉淀的原因主要是水中钙镁离子，此外还有铁锰铅锌等其他金属离子，但由于钙镁离子浓度远远大于其他离子的浓度。因此，通常以钙镁含量来计算水中硬度。测定水中硬度有经典的乙二胺四乙酸二钠容量法。现讨论测定水中钙镁离子浓度计算水中硬 Water hardness refers to the degree of precipitation of soap, soap precipitation is mainly due to calcium and magnesium ions in water, in addition to iron and manganese, lead and zinc and other metal ions, but the concentration of calcium and magnesium ions is far greater than the concentration of other ions. Therefore, the water hardness is usually calculated as the content of calcium and magnesium. Determination of water hardness of the classic disodium edetate capacity method. Now discuss the determination of calcium and magnesium ions in the water to calculate the concentration of water hardness