Some liquids are dangerously cold. Liquid nitrogen, helium, neon and oxygen would almost immediately freeze anything you dip into them. The coolest liquid we know on Earth is liquid helium. Naturally, none of these elements exist as liquids on Earth. They have to be cooled before they become liquids. In liquid form, the temperature of helium is around -269 centigrade. Liquids like these are used to keep some machines cool, especially machines that use super conducting magnets like magnetic resonance imaging machines. Sometimes, a doctor may use liquid nitrogen to burn off abnormal growths on the skin.