Solute transport models often use batch‐generated adsorption isotherms to partition solute between the aqueous and adsorbed phases, but the relationship at equilibrium between aqueous and adsorbed solute concentrations may be different in closed (batch) and open (flow) systems. Adsorption isotherms were generated for orthophosphate/goethite, silicate/goethite, orthophosphate/soil clay and orthophosphate/arsenated‐goethite systems using batch and flow (miscible displacement) techniques. The contact times were 168 and 96 h in the batch and flow experiments, respectively. The shapes of the isotherms generated by the two methods were very similar in all cases, although the flow‐generated isotherms were displaced slightly upward relative to the batch isotherms. Simple Langmuir plots of both batch and flow data were nonlinear for all systems, while in all systems containing phosphate, flow‐generated distribution coefficients were greater than the corresponding batch‐generated values, particularly at low surface coverage. In addition, adsorption maxima and values of the two‐surface Langmuir parameter b1 were consistently greater in the flow systems. The results indicate that provided transport processes do not keep the flow system far from chemical equilibrium, batch‐generated anion adsorption isotherms are likely to underestimate the extent of adsorption in the corresponding flow system, particularly at relatively low aqueous phase sorbate concentrations. This appears to be due, in part, to the removal of competitive antecedent species in the flow system effluent. It is suggested that flow systems are thermodynamically equivalent to batch systems having very wide solid/solution ratios.

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Two main theories have been proposed to explain the specificity of uptake of sugars by human erythrocytes. The membrane theory (see for example, Bowyer & Widdas, 1956;LeFevre, 1954) suggests that the main barrier to diffusion is the cell membrane and that transfer across this barrier can occur only as a result of binding of the penetrant by a specific agent or carrier located in the membrane. Once inside the cell, however, the sugar is free to diffuse throughout the aqueous phase of the protoplasm. The 'sorption' theory (Troshin, 1961) on the other hand suggests that all the water within the protoplasm is bound, so that the solubility of the sugar in the aqueous phase of the cell is less than in free water.Specific binding of various compounds by the cell colloids is supposed to occur, however, and to account for at least part of the sugar appearing in the cell.The present work seeks to determine the amount of binding of sugars occurring in human erythrocytes. To this end measurements were made of the amount of sugar entering cells whose volume was adjusted by varying the tonicity of the medium in which they were suspended. It would be expected that if all the sugar in the cells were bound the amount taken up by a given number of cells would be independent of their volume, since the amount of cell protein and hence the number of binding sites should be constant. On the other hand if the sugar was in solution within the cell the amount taken up would be proportional to the volume of free (or solvent) water present in the cell.It was also the purpose of the present work to measure the kinetics of sugar uptake by cells of different volumes in an attempt to decide whether the greater resistance to diffusion occurs in the membrane or within the protoplasm. Since the surface area of erythrocytes remains constant as the cell volume is varied, the rate of sugar uptake should be independent of the volume if the membrane provides the greater resistance.

The simplest biological transport system so far extensively investigated is that of monosaccharides in human erythrocytes. Despite its simplicity there is still considerable doubt and divergence of opinion concerning its mechanism. Some confusion may arise as a result of the comparison of diverse data obtained by different workers using a variety of experimental techniques. To minimize this problem, an attempt is made here to repeat, under standard conditions and with as much care as possible, five of the more definitive types of experiments previously performed on this system. It is hoped that the result of this effort is an internally consistent set of data with which the quantitative predictions of various proposed mechanisms may be compared as a primary criterion for their acceptability.

Measurements of the rate of loss of sugar from human erythrocytes into sugar-free solutions were made as a function of sugar concentrations. The half-saturation concentration of this process was found to be different from those half-saturation concentrations previously measured by other methods. These data, together with a number of similar data from former publications, are summarized in tabular form and their use in assessing postulated transport mechanisms is illustrated by consideration and rejection of a mechanism in which the transport process is assumed to be the result of a protein conformational change.