First of all 1/500 solution of oleie acid is prepared in alcohol by dissolving 1 cm3 of oleic acid in 500 cm3 of alcohol. Put n drops of this solution on the surface of water. Thus a film of oleic is formed. This film is stretched so that its thickness is just equal to the molecular size. With passage of time, alcohol is evaporated and a with layer of oleic acid is formed on the surface on water.
The area of thin layer is measured with a tracing paper and a grapn paper.
Volume of n drops = nv
Volume of oleic acid in n drops of solution
= nV X 1/500 cm3.
Now thickness of film = Volume of film/Area of film
t = nv/500 x 1/A cm
Since thickness of film is equal to the molecular size and hence size of the molecule can be Calculated.
