You will need
  • two identical thermometer, a piece of gauze, the hair psychrometer psychrometric table table of the dew-point.
Determination of relative humidity through the point resistente the temperature of the air and using the table to determine the saturated vapor pressure at a given temperature. Then collect a sample of air and cool it, by constantly monitoring the temperature until the water vapor in it begins to condense, forming dew. Measure the temperature at this point and using the table to determine the saturated vapor pressure. It will be equal to the actual vapour pressure at reference temperature. After that divide the vapor pressure obtained by cooling the saturated vapor pressure at a given temperature, and multiply the result by 100%. The result is relative humidity in percent.
The definition of relative humidity two will thermometrically two of the same thermometer. The best fit liquid mercury thermometers. On the bubble with the fluid of one of them wrap the cheesecloth, then wet it with water. After waiting some time, read thermometers in degrees Celsius. Then find the temperature difference between the wet and dry bulb thermometer readings wet bulb thermometer will be either the same or lower than the dry. In a psychrometric table, locate the column of the dry bulb temperature and look closest to what was demonstrated by the measurement. Then the line find the value that matches the calculated difference in the readings of dry and wet thermometers, the cell will be the relative humidity of the air in percent.
Determine the relative humidity the hair gidrometpostavka horse hair changes its length depending on the humidity of the air, pull it and attach to a sensitive dynamometer. The tension force can determine the relative humidity of the air. This measurement is the least accurate.