As for the evaporation crystallization method, it was naturally a method of obtaining saltpeter after it was dissolved in water and then boiled or dried.
Jiang Yue also mentioned the temperature-lowering crystallization method. It was said that the dissolution of saltpeter in water would decrease as the temperature of the water decreased. In the end, the dissolution would be so small that crystals would be produced, which would produce saltpeter.
Since it was frozen, the temperature must be very low. Even if the soluble saltpeter was not completely separated, most of it would be seen on the surface of the ice. At that time, he could directly scrape off the saltpeter crystals from the surface of the ice and reuse them.
As for the small amount of saltpeter that was still in the ice, it could be obtained after the ice had melted, boiled, or dried.
