Traditionally, the soil in the kitchen is the best for making salt. Is there any soil in the kitchen? Do I need to cover the iron pot with a lid when making it?

Nitre is extracted from the soil. The traditional tools for making salt are very simple, just a big iron pot, and the raw material is soil. It is said that it is best to use soil from the kitchen, because frequent cooking and cooking will precipitate a lot of saltpeter. After putting the soil into the iron pot, keep adding water to boil it. After a day or two, a layer of white saltpeter will form on the edge of the iron pot.