Caustic soda also has a working grade, reagent grade and so on, but now most of the production to take into account the cost of the problem, many manufacturers are using industrial grade alkali to do hand soap, as soap for the alkali, Also, high purity. The natural cost is also higher. Because of the soap, many people are accustomed to adding some other substances, the purity is even worse, so you can not care about 1 ~ 2% of the NaOH impurities. With industrial-grade NaOH cheap, and use and no problem, so do soap with this level of soap on it. But even the industrial grade of caustic soda should also be high purity of this relatively high security point.