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Does hot water cool faster than cold? In 1977 Jearl Walker observed the time taken for a beaker of water to reach 0 °C from a range of initial temperatures and in a number of different conditions: 50 ml of water in a small Pyrex beaker (yellow); 50 ml of water in a large beaker (dark blue); 50 ml of water in a large beaker in a frost-free freezer (light blue); 100 ml of water in a large beaker, with the thermocouple (thermometer) near the bottom of the beaker (green); 100 ml of water in a large beaker, covered with plastic food wrap, with the thermocouple near the bottom (purple); and 100 ml of water in a large beaker, with the thermocouple near the top (red). The Mpemba effect is seen in the portions of the graphs that have a negative gradient.