Phase transitions. Ice in a beaker is heated over a propane Bunsen burner flame while temperature is measured with a digital thermometer. Initially temperature of the ice is -1.1C (frame 1 from left). As ice melts, the temperature of the ice-water mixture stays constant at 0C (frames 2 and 3). After all ice is melted, water temperature rises (frame 4) until water starts to boil and temperature stays at +100C (frame 5). Boiling is characterized by water vapor bubbles appearing at the bottom and rapidly rising to the top.