Take a vessel with water and put a small amount of ammonia powder in it. The powder, dissolving in water, greatly lowers its temperature. Then they take a second vessel with water and, placing it in the former vessel, put ammonia powder into it as well. Then the water will cool even more. Then take the third vessel, put it in the second one, fill it with water and put ammonia powder there. The water will get even colder. The same is done with the fourth vessel. Finally, a glass of clean water is placed in the fourth vessel. Freeze water in a glass.