The fatty acid counter ion has a large effect on the properties of soap. If sodium is used as the counter ion, the solidiication point and the hardness normally increase, and it is easy to adjust the shape as solid soap. On the other hand, the solubility in cold water and the foaming property decrease, and they tend to decrease the cleansing power and the feeling in use. In contrast to this, if potassium is used as the counterion, the solubility in cold water and the foaming property are largely improved. However, the solidification point and the hardness significantly decrease, and production suitability as solid soap and the shape-retaining property deteriorate. Therefore, potassium is widely used, as the counter ion, for liquid soap (liquid body soap etc.). However, the application of about 20% of potassium has virtually been the limit for solid soap.