Difference Between Partial Pressure and Vapour Pressure 1.b 1. Vapour Pressure Take a liquid like H2O, Alcohol etc. in a container and put some Mercury (Hg) in the additional U Tube. Now start heating the container. Results. 'Evaporation start'. This vapour start exerting pressure on Mercury colomn. One side of Mercury level increases to height h. Now P=dgh (d=density of liquid, g= gravitational acceleration, h= height of colomn) 2. Partial Pressure Take some container of same size and some gases like CO2, O2, NE separately and measure pressure of gases. Measure the pressure isolately. Now mix all the gases and now measure pressure of container. Now read the following image.