The phenomenon of rise or fall of liquid level in a capillarity tube is called as capillarity. In non-wetting liquids (e.g. mercury), what is the relation between cohesion of mercury and adhesion between mercury and capillary tube?

Explanation:

Capillarity: 

• Capillarity is defined as a phenomenon of rise or fall of a liquid surface in a small tube relative to the adjacent general level of liquid when the tube is held vertically in the liquid.
• The rise of liquid surface is known as capillary rise while the fall of the liquid surface is known as capillary depression.
• The attraction (adhesion) between the wall of the tube and liquid molecules is strong enough to overcome the mutual attraction (cohesion) of the molecules and pull them up the wall. Hence, the liquid is said to wet the solid surface. 
• It is expressed in terms of cm or mm of liquid. Its value depends upon the specific weight of the liquid, diameter of the tube and surface tension of the liquid.

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• Capillary rise is given by:  \(h=\,\frac{4 \,\sigma\,cos\theta}{\rho \times\,g\times \,d}\), The value of θ between water and clean glass tube is approximately equal to zero.
• If θ  is less than 90° , the liquid is said to "wet" the solid. However, if θ is greater than 90°, the liquid is repelled by the solid, and tries not to "wet" it.

• For example, water wets glass, but not wax. Mercury on the other hand does not wet glass.

∴ In case of non-wetting liquids (e.g. mercury), cohesion is greater than adhesion.