Humidity is the water content in liquid or vapor in the air, construction materials, fuel, materials, soil, food products etc.
To characterize air humidity are the following parameters: maximum humidity, absolute humidity, relative humidity, lack of saturation. At a given temperature in 1 m3 of air can contain a certain maximum amount of water vapor is the maximum air humidity in the state of saturation. If on reaching saturation state to lower the temperature of the air, part of the water vapor will be allocated in the form of dew or frost (at temperature below 0 degrees). The content of water vapor in the air under these conditions is called the absolute humidity. The temperature at which the absolute humidity maximum is called the dew point. Maximum humidity and absolute measured by the pressure of water vapor and are expressed in millimeters of mercury (or millibars) or weight units - in grams per 1 m3 of air. Relative humidity is expressed as the percentage ratio of absolute humidity to the maximum. The difference between the maximum humidity and absolute called " lack of saturation.
In medical climatology and sanitary practice we often use the concept of relative humidity and lack of saturation, because they allow you to judge the influence of humidity on the human body. Most meets the requirements of comfort, relative humidity, equal to 30%to 60%. For measurement of humidity of atmospheric air and air of premises of inhabited and public buildings, and industrial premises used the psychrometers (see), hygrometers. Registration of changes of humidity within a certain period of time using hygrographs with recording device.
Universal methods of determining the moisture content of building materials, soil, food products etc. do not exist.
Depending on the put in the study tasks using different methods - weight, chemical and other