Water, Ice, and the Triple Point:
• Water, composed of hydrogen and oxygen, is the primary source of water on Earth. Its density is the most important fact about water, being densest at +4°C.
• Ice, 10% less dense than water, floats with 90% of its bulk under-water. Water supercools, staying liquid below 0°C its solidus temperature.
• The temperature of pure ice and water is +0.0025°C, not 0°C as most people assume. This is due to water rapidly absorbing air, causing air saturation.
• The mixture of ice/water and water vapor in equilibrium is the water triple point, with its temperature being 0.01°C by definition.
• The triple point of water was recognized as a key temperature in the development of international temperature measurement standards.
• John Stimson developed a water triple point cell with an attached flask for transferring contents and redistilling them back into the cell.