The gaseous form of water formed when water boils. At atmospheric pressure, steam is produced at 100^ºC by boiling water. It is widely used in the chemical and process industries as a utility for heating processes such as in kettle reboilers for distillation columns. It is also used in power generation where steam is produced or ‘raised’ from a thermal or nuclear process and expanded through turbines. Scottish engineer James Watt (1736–1819) understood the value of steam and his improvements to the Newcomen steam engine were an important contribution to the Industrial Revolution. Other uses of steam include sterilization, which is used in the food and medical industries. Steam is effective at destroying harmful pathogens and is a harmless substance once cooled. Wet steam is water vapour that contains water droplets. When heated further, the water evaporates. The dryness fraction of steam is the ratio of the amount of water in steam to the total amount of water vapour. Superheated steam is produced by heating the steam above the boiling point of water. The thermodynamic properties of steam are presented in published steam tables.