Soap is made by cooking with fat and caustic soda. The soap contains about 30% of water. If you dry it, it will not only evaporate the water and shrink and crack, but also separate the internal oil and caustic soda. It becomes an acid fat, and caustic soda becomes soda ash by absorbing carbon dioxide in the air, so the decontamination ability of soap is reduced. From this we can infer:. ['Shrinking dry and cracked soap and 30% water can restore the original decontamination ability.', 'Soda ash has no decontamination ability.', 'Soap without any of grease and caustic soda will not have the ability to decontaminate.', 'It is the moisture in the soap that combines the oil and caustic soda.']