A process for separating an aqueous mixture of penicillin and acids associated therewith in its manufacture different members of the mixture having different dissociation constants, comprises contacting the solution with a substantially neutral organic solvent for the mixture under conditions to form two phases, a solvent extract and a residual aqueous solution, separating the phases and washing the solvent extract with water whose pH value in equilibrium with the solvent extract is between that of the original solution and substantially neutral.  The aqueous and solvent phases may flow countercurrently to each other.  Examples of solvents and buffers are given.  In a comparative example, an aqueous penicillin solution (derived from a surface culture) was acidified with sulphuric acid to a pH of 2.0 and divided into positions.  One portion was batch extracted with chloroform and the solvent extract treated with a dilute aqueous sodium bicarbonate solution to produce an aqueous solution of the sodium salt of pencillin, which on evaporating to dryness contained penicillin in a concentration of 169 Oxford units per mg.  The other portion was similarly treated with chloroform, but the solvent extract was washed with distilled water before treatment with the bicarbonate solution.  The dry salt was found to have a penicillin concentration of 310 Oxford units per mg.ALSO:A process for separating a mixture of organic water-soluble electrolytes, which tend to change their number of protons, from an aqueous solution thereof, different members of the mixture having the same tendency but different dissociation constants, comprises contacting the solution with a substantially neutral organic solvent for the mixture under conditions to form two phases, a solvent extract and a residual aqueous solution, separating the phases and washing the solvent extract with water whose pH value in equilibrium with the solvent extract is between that of the original solution and substantially neutral.  The aqueous and solvent phases may flow countercurrently to each other.  In a preferred embodiment the aqueous solution in combination with spent wash water produced in the second step of the process is caused to flow through an extraction zone countercurrently to the organic solvent, and the resulting aqueous and solvent phases separated from opposite ends of the zone, the solvent phase is then introduced into one end of a washing zone and water admitted into the other end to result in a pH which is between that of the original solution and substantially neutral, the solvent phase is washed countercurrently with the water, the resulting washed solvent phase and spent water are separately removed from the washing zone and the wash water combined with the aqueous solution.  In a further modification, the organic solvent and water are introduced at the opposite ends of an extraction zone, the solution admitted at a point intermediate the ends, and the resulting solvent and aqueous phases caused to flow countercurrently to each other after which they are withdrawn from opposite ends of the extraction zone.  Buffers which may be used during extraction and scrubbing include: bicarbonates, bisulphides, phosphates, meta-phosphates, sulphites, oxalates, citrates for the separation of acids and chlorides, bromides, sulphates, nitrates of ammonia, hydrazine, hydroxylamines, ethanolamines and ethylene diamines for the separation of bases. Examples of mixtures of water-soluble organic acids or bases which may be thus separated according to their strength are: lower fatty acids or chlorinated fatty acids, acids resulting from certain fermentation processes, particularly those obtained in the manufacture of penicillin, fruit and vegetable juices containing various acids, bases obtained in the ammonolysis of chlorinated hydrocarbons having up to 5 or 6 carbon atoms in the molecule, amino acids obtained from proteins and certain alkaloids.  Examples of solvents are various organic liquids or mixtures thereof such as propane, butanes, pentanes, hexanes, heptanes, octanes, benzene, toluene, xylenes, cumene, tetraline; gasoline, naphthas, kerosene; methyl chloride, chloroform, carbon tetrachloride, ethyl chloride, ethylene di-chloride, trichlorethylene, tetrachlorethane, propyl chloride; n-butyl    alcohol, amyl alcohol and hexyl alcohols; methyl butyrate, valerate or caproate, ethyl propionate, butyrate or valerate, propy acetate, propionate, butyrate or valerate; butyl and amyl formates, acetates and higher esters; methyl ethyl ketone, di-ethyl ketone, methyl isopropyl ketone, di-isopropyl ketone, methyl isobutyl ketone, di-isobutyl ketone; ethers, amines and imines which are substantially water-insoluble; and alkyl phenols.