Dr. Andrews compares the irregular molecules of water to the regular ones of ice and explains that ice floats because it is less dense than water. He then shows a diphenyl oxide molecule model and explains that it freezes at room temperature and sinks and is therefore used to remove impurities from a liquid. He demonstrates how skating on ice creates pressure causing ice to melt enough to allow gliding on water, which couldn't be done if the water froze at a lower temperature. Dr. Andrews points out that the molecules of iron in a drill and sodium chloride in salt are arranged in a regular pattern and are therefore "frozen." He then adds liquid nitrogen to water, alcohol, glycerin, and molasses to compare the differing results. Ways of measuring temperatures include household thermometers, Beckmann thermometers (accurate to 1000th degree), and electrical thermometers such as platinum resistance, thermocouple, and bolometer (measuring to the millionth of a degree).