crude salt is a kind of salt containing a small amount of sediment. The purification of crude salt is the process of dissolving (separating insoluble matter from salt), filtering (completely removing insoluble matter) and evaporation (separating salt from solution to obtain salt). In the evaporation process, the glass rod is used to stir, so as to prevent the local temperature from being too high, resulting in liquid splashing.

Sodium hydroxide solution can react with magnesium chloride to generate magnesium hydroxide precipitate and sodium chloride, and sodium carbonate solution can react with calcium chloride to generate calcium carbonate precipitate and sodium chloride, so calcium chloride can be removed by adding excessive sodium carbonate solution, and the chemical formula of sodium carbonate is Na2CO3．. After adding excessive sodium hydroxide solution and excessive sodium carbonate solution in turn, Magnesium hydroxide and calcium carbonate can be removed by filtration, and the obtained sodium chloride solution contains sodium hydroxide and sodium carbonate. When an appropriate amount of dilute hydrochloric acid is added, dilute HCl can react with sodium hydroxide to generate sodium chloride and water, and can react with sodium carbonate to generate sodium chloride, water and carbon dioxide, so as to remove sodium hydroxide and sodium carbonate, and finally obtain sodium chloride solution, and then evaporate and crystallize the filtrate to obtain more pure sodium chloride.

Therefore, the answer is: filtration; Stir; Na2CO3； Dilute HCl．