In the ancient world, people used snow and ice to cool foods, but these natural refrigerants were in short supply during hot weather. Early scientists searched for a more reliable coolant, and someone discovered that putting saltpeter (potassium nitrate) in water produced a very cold liquid. By the mid-sixteenth century, Italians knew about this phenomenon and used it to make frozen concoctions called ices. See italian ice. The French also learned the secret, and recipes for ices were published in Europe before 1700.