WATER (H2O)

The liquid that descends from the clouds in rain and which forms streams, lakes, and seas, and is a major constituent of all living matter. Pure water consists of Hydrogen (11.188 percent by weight) and Oxygen (88.812 percent by weight) in the proportion of two atoms of hydrogen to one of oxygen (H2O), and is an odorless, tasteless, transparent liquid which is very slightly compressible. It has a slightly blue color which is observable only in thick layers of the liquid. At its maximum density, 39.2°F (or 4°C), it is the standard for specific gravities, one cubic centimeter weighing one gram. Water's weight per gallon (at 15°C or 59°F) is 8.337 pounds (3.772 kilograms). It is also the standard for specific heats. Its own specific heat is very great. It freezes at 32°F (0°C) and boils at 212°F (100°C) under atmospheric pressure at sea level. Pure water is an extremely poor conductor of electric current, although many Aqueous (water-based) solutions are conductors. Water is the most important of solvents, dissolving many gases, liquids, and solids. Natural waters of the earth, as those of springs, rivers, or the oceans, contain more or less dissolved matter, which is mostly removed by distillation. Rain water is nearly pure. Water is important chemically as a solvent and dissociating agent, as a catalytic agent, and often as one of the substances taking part in a chemical reaction. Ordinary water, described above, is a mixture of molecules containing hydrogen of atomic weight 1, with a small proportion (about 0.015 per cent) of molecules containing hydrogen of atomic weight 2. This later kind of water, termed Heavy Water or Deuterium Oxide, D2O, can be separated by fractional electrolysis or distillation and in other ways and is used as a moderator in certain nuclear reactors.