Zigong City, Sichuan Province, is known as the salt capital of the millennium, the method of drilling wells to produce salt is: first, drilling wells on the ground to the salt rock layer, and then hig

(2) due to the solubility of sodium chloride is not affected by the temperature change is not very large, so it is usually used to evaporate the solvent method of crystallization;

(3) the substance in the different solvents have different solubilities, with saturated sodium chloride (2) repeated washing (2) crystallization of salt, you can remove calcium chloride impurities, because saturated sodium chloride solution can no longer dissolve sodium chloride but can dissolve calcium chloride;

(4) according to the characteristic reaction of calcium ions: can be reacted with carbonate to produce a white precipitate to test.

The answers are:

(1) Nitrogen fertilizers from paddy fields flow into salt wells and river water;

(2) Evaporation and crystallization, the solubility of sodium chloride doesn't change much with temperature;

(3) Saturated sodium chloride solution can't dissolve sodium chloride any more but it can dissolve calcium chloride;

(4) Take the drenched solid dissolve it in water, then drop sodium carbonate solution, if there is no white precipitate, it no longer contains calcium chloride.