Multistage extraction: Hunter-Nash Method It is proposed to reduce the concentration of acetaldehyde in aqueous solution from 50 per cent to 5 per cent by mass, by extraction with solvent S at 293 K. If a countercurrent multiple contact process is adopted and 100 kg/s of the solution is treated with an equal quantity of solvent, determine the number of theoretical stages. The equilibrium relationship for this system at 293 K is as follows: 100% Acetaldehyde 50 50 50 100% Water 100% Solvents