Gypsum is anhydrous calcium sulfate, which can react with water and give off heat. The purpose of first frying gypsum is to complete the hydration reaction of gypsum alone. What is dissolved in water is calcium ion and sulfate ion, and what is not dissolved is calcium sulfate hydrate. In the prescription, if the doctor specifies that gypsum should be decocted first, the correct way should be to mix the remaining decocted soup with the decocted liquid, so as to reduce the combination of calcium ions and tannins in the liquid and precipitate.