Polarographic techniques are employed in the investigation of Chl a dihydrate formation and aggregation in binary solvent mixtures of water/acetone. The variation of the relative intensities of two observed polarographic peaks, at 2 −1100 and −1200 mV, with the composition of the binary solvent supports a shift in the equilibrium in favor of the formation of chlorophyll a dihydrate, Chl a · 2H 2 O, from the acetone solvate, Chl a · Ac, as the water concentration is increased. It is concluded that the equilibrium further shifts towards the dimerization of Chl a · 2H 2 O at water concentrations exceeding 40% (volume). A third polarographic peak at −1434 mV, observed in 50:50 (v/v) water/acetone solutions at Chl a concentrations greater than 1·10 −5 M, is attributed to the oligomer of Chl a dihydrate, (Chl a ·2H 2 O) n . From the amount of electricity calculated from the polarographic peaks, the coverage areas, 259 and 597 A 2 , are respectively obtained for the adsorbed monomer, Chl a ·Ac, and dimer, (Chl a ·2H 2 O) 2 , at the electrode surface.
