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The desorption of specifically adsorbed (ligand exchanged) anions, such as phosphate, selenite, and fluoride, from the surface of gibbsite and goethite has been studied by repeatedly washing the adsorption complex with solutions of constant pH and ionic strength but containing no specifically adsorbable anions. The desorption of the anions varies between complete reversibility and almost complete irreversibility. Measurements of surface charge by the uptake of Na+ and C1-revealed that, on washing the adsorption complex, the surface charge returned to its value at the given pH in the absence of specifically adsorbed anions. Thus when the isotherm was irreversible, OH-was desorbed (or H+ adsorbed) in preference to the desorption of the specifically adsorbed anion, whereas when the isotherm was reversible the specifically adsorbed anion was desorbed.Irreversibility appears to involve the nature of the adsorption complex at the surface. Where only monodentate ligands form, for example fluoride adsorption, the isotherm is reversible, whereas bridging or multidentate ligands and the formation of ring structures at the surface favour irreversibility. whic g are involved in the desorption of specifically adsorbed anions,

Sorption of boron by Kent sand kaolinite, WilIalooka illite, and Marchagee montmorillonite in 0.01M CaCl2 is consistent with a mechanism described by the Langmuir equation, except that deviations occur at solution concentrations greater than about 10 �g B/ml. The quantity of boron adsorbed increases markedly with pH, and is rapid, reversible, and unaffected by the concentration of calcium chloride present. Complete desorption of surface boron, without significant solution of lattice boron, is achieved with 0.01M mannitol solution. Comparing the three clays at pH 7.5 on a surface area basis, the illite is most reactive (1.18 �g B/m2), followed by the kaolinite (0.28 �g B/m2) and the montmorillonite (0.02 �g B/m2). For illite, which is the most reactive of the three minerals, the magnitude of the above values emphasizes the small proportion (less than 1.4%) of the total surface area occupied by boron. Consideration of the reaction between boron and clays suggests that either boric acid molecules or borate ions could be the adsorbed species. Increasing sorption with pH could be explained either by the increasing proportion of borate ions to boric acid with pH or by a greater number of sites on the clay surface at higher pH values.

The amounts of Na+, Mg2 +, K+, Ca2 +, C1-, SO42-, HCO3- and dust precipitated in rainfall and as dry fallout into continuously open collection funnels are reported for 59 centres throughout Western Australia. Ionic accessions for 1973 were in the following ranges; Na+, 2-98 kg ha-1; Mg2+, 0.3-15 kg ha-1; Ca2+, 0.8-35 kg ha-1; K+, 0.3-14 kg ha-1; SO42-, 2-57 kg ha-1; C1-, 2-180 kg ha-1; HCO3-, 1-105 kg ha-1. Chloride deposition at the coast is approximately an order of magnitude greater in the south-west of the state than in the north. In each region the amount of chloride precipitated exhibited the usual decrease with distance inland. There were regional differences in rainwater salt composition. Excess of ions over the amounts attributed to oceanic aerosols are explained by the locations of sampling centres relative to other source areas. Perth, the largest city, had the highest excess sulphur and above average values were obtained at the larger mining and country centres. Industry and domestic fires are the probable sources of this sulphur. Excesses of all ions from terrestrial sources were indicated at many inland centres, and were greatest in the zone of salt lakes and occluded drainage in the south-west.