How does mist form

Why is it that no dew forms if the air pressure is low, however cool the air temperature  

To understand this question, we must first appreciate how molecules come closer together when applying a pressure. The Irish physical chemist Thomas Andrews (1813-1885) was one of the first to study the behaviour of gases as they liquefy most of his data refer to CO2. In his most famous experiments, he observed liquid C02 at constant pressure, while gradually raising its temperature. He readily discerned a clear meniscus between condensed and gaseous phases in his tube at low temperatures, but the boundary between the phases vanished at temperatures of about 31 °C. Above this temperature, no amount of pressure could bring about liquefaction of the gas. 

Andrews suggested that each gas has a certain critical temperature, above which condensation is impossible, implying that no liquid will form by changes in pressure alone. He called this temperature the critical temperature 7(crjticai). 

The critical temperature 7 (Crjticai) is that temperature above which it is impossible to liquefy a gas. 

Critical fluids are discussed in Chapter 5, where values of critical) are listed. 

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