The ancients used saltpeter to make ice, just like the magic of nature, full of magical charm.
Saltpeter, also known as natural potassium nitrate, is a white crystalline substance. It is widely distributed in desert and grassland areas and is a common refrigeration raw material for ancient people.
To use saltpeter to make ice, you first have to choose a place to shelter from the sun and wind, and dig a deep pit one meter deep, two meters wide and three meters long. Then, the bottom of the pit is covered with saltpeter with a thickness of about ten centimeters. Next, pour clean water into the pit and allow the saltpeter to dissolve thoroughly.
At this point, a miraculous phenomenon occurred. The saltpeter in the water begins to absorb heat, and the temperature drops rapidly. It wasn't long before the water began to freeze. If you look closely, you will notice that the ice starts at the bottom of the pit and gradually spreads out in all directions.
The process of making ice requires patience and time. In general, it takes about four hours from pouring clean water to completely freezing. During this time, you can hear ice cubes "crunching" growing in the pit. The sound is a wonderful sense of pleasure.
The prepared ice cubes are crystal clear, like gemstones. The ancients used to use these ice cubes to cool off the heat in the hot summer. And this method of making ice from saltpeter has also become a kind of life wisdom of ancient people.