3. In olden days, when there were no refrigerators or availability of ice, ice cream was made by adding potassium nitrate to water to chill a container to -20C, making it possible to freeze the cream-sugar mixture. The container with the salt-water never froze, and remained as a liquid solution. Explain why no solid ice or slush was observed in this container, even though the temperature was well below 0, the freezing point of water