Lowering in vapour pressure is determined by Ostwald and Walker dynamic methed. It is based on the prinicipal , that when air is allowed to pass through a solvent or solution, it takes up solventvapour with it to get itself saturated at that temperature
I and II are weighted separately before and after passing dry air. Loss in mass of each set, gives the lowing of vapour pressure. The temperature of air, the solution and the solvent is kept constant.
Loss in masss of solvent (`w_(II)`)will be proportional to :
