Effect of temperature:

The surface tension of all liquids decreases linearly with rising temperature, over small temperature ranges, so that surface tension \( T_t \) at \( t^{\circ} \)C is given by,

\( T_t=T_0(1-\alpha{t})\tag{1} \)

where, \( \alpha \) is the temperature coefficient of surface tension, \( T_0 \) is the value of surface tension at \( 0^{\circ} \)C.

At the critical temperature, the value of surface tension is zero, there is no surface tensional effect.

Van der Waals suggested an emperical relation given by,

\( \displaystyle{T=A{(1-\frac{\theta}{{\theta}_c})}^{\frac{3}{2}}\tag{2}} \)

Where \( {\theta}_c \) is the critical temperature, \( A \) is a contant for a given liquid, \( T \) is the surface tension at absolute temperature \( \theta \).

Ferguson gave another modified emperical formula given by,

\( \displaystyle{T=A{(1-\frac{\theta}{{\theta}_c})}^n\tag{3}}\)

Where \( n \) is a constant which varies for different liquids and for most of the liquids, it is 1.21.