Dissolve an appropriate amount of cerium oxide in a 50% hydrochloric acid solution and heat it with a steam bath. Normally, cerium oxide can be completely dissolved. If there is a small amount of oxide residue at the bottom of the container, it needs to be filtered. Heat the obtained clear solution on a 75 ℃ water bath to remove most of the solvent. After cooling the solution, crystals precipitate. Filter the crystal, place it in a vacuum dryer filled with granular sodium hydroxide and Magnesium perchlorate, vacuumize and dry it to obtain hydrated cerium chloride.