Gases which follow the above laws exactly are called perfect or ideal gases. Gases in reality follow these laws only approximately and the more closely the lower the pressures are. 1p in Pascal = N/m2
Diagram 2.3.4.1
If the gas approaches a vapour like state or if it contains a significant constituent of water vapour, one uses the introduction of a real gas factor Z (diagram 2.3.4.1) in order to effect a correction when calculating the volume. For pure air, and with absolute pressures lower than 40 bar and temperatures below 50°C, the real gas factor can be close to 1 and is, therefore, neglected in most cases. Vapours and real gases only approximately obey the relation p x v = R x T. If steam tables or steam diagrams are available, the appropriate state parameters can be derived from these. These are based on measurements and interpolation calculations.
Formula 2.3.4.1
Another possibility of establishing the real status parameters of gases, consists of supplementing the state equation with the correction factor Z from diagram 2.3.4.1 so that, at high pressures or temperatures, solely formula 2.3.4.1 is valid when an accurate determination of the volume is made.
