One of the chemical compounds having the defining value for existence of all types of life on Earth is water. As well as other substances, it can be in different aggregate states. One of them - water vapor.
Water vapor represents gaseous aggregate state of water. It is formed by its separate molecules in the course of evaporation. Water vapor under normal physical conditions is absolutely transparent, has no smell, taste and color. However at condensation of the saturated steam of water mixed with other gases the smallest drops can be formed. They effectively scatter light. Therefore in a similar state it is possible to see water vapor.
On Earth of couple of water contain in the atmosphere. They play an important role in course of various natural processes and also directly influence activity of plants, animals and people. Content of water vapor in air is called humidity. Distinguish absolute and relative humidity. For receiving an indicator of humidity of air hygrometers or psychrometers use devices.
Today water vapor takes the major place in the industry and many industries of the equipment. It is used as a working body when transforming thermal energy to kinetic and electric by means of different steam-engines - steam-power installations, steam turbines. Because of rather high thermal capacity and an opportunity to be heated to temperature above 100 °C, water vapor is widely applied and as the heat carrier. For example, in the systems of steam heating. Studying water vapor began in the 16th century. The first scientific work devoted to its properties was published in the 17th century by J. Port. With wide circulation of steam-engines in the 19-20th centuries water vapor drew attention of scientists again. So, in the middle of the 20th century serious researches of behavior of steam on ultrahigh pressure were made. Results of researches were stated at the fourth international conference on properties of water vapor which was taking place in New York in 1963.