The crude salt used in hot compress is sweet and salty, and it is non-toxic. Light yellow iron hydroxide, light red anhydrous iron oxide, brown or black organic spherical polymer or crystal, etc. , the surface is fatty luster. It is valid for 5 years and can be reused for 4 years. Because sea salt is an effective mineral for gasification, it can be repeatedly crystallized in the bag. At first, the bag will shrink quickly, but the total weight has not changed. When the big gap between salt particles is filled with newly crystallized sea salt, the volume of the whole bag will not shrink. Because it absorbs water easily, it can be put in a plastic bag in wet climate, and sea salt can be dried when it is wet.