Calcium hydroxide plays a role in lime water for ice powder, which will react with carbon dioxide dissolved in water to produce calcium carbonate and fail. When the temperature rises after boiling, the solubility of gas will decrease, including the concentration of carbon dioxide, so it will not affect the concentration and function of calcium hydroxide. After limewater is left for a long time, carbon dioxide will slowly react with calcium hydroxide, and finally all calcium hydroxide will be converted into calcium carbonate precipitation, and then limewater will be ineffective.