The angle inside the liquid between the tangent to the solid surface and tangent to liquid surface at point of contact is known as angle of contact for that pair of solid and liquid. The angle of contact for those liquids which wet the solid is acute, it is zero for pure water and clean glass, for glass and alcohol also it is zero, for glass and mercury it is 138∘, silver and water 90∘ and for water and chromium 160∘ .