Abstract: Seven methods are proposed for estimation of extraction constants as follows.1. The relation:- (pH₁/2 )_1.0= AZ²/r + BX_±+ C-λ(_n-1)+(lgK⁰_dm+a)/n+lgK_aK_d^-1 Linear relations between- (pH_1/2 )_1.0 for two similar cations being extracted with a series of extractants;3. Linear relations between- (pH_1/2)_1.0 for two similar extractants extract a series of cations;4. Linear relations between- (pH_1/2)_1.0 for two diluents;5. Linear relations of-(pH_1/2)_1.0 vs. Z²/r for cations with similar electronegativity value;6. Normal variation of extraction for a series of cations in accordance with Z²/r and electronegativity values;7. Extractants of large ∑_pK_a match closely with cations of large Z²/r, and extractants of small electrouegativity match closely with cations of large electronegativity.