Fig. 2. Sorption of total organic C (TOC) by sample clays (see Table 1) at room temperature (18°C) as a function of the concentration of xanthan at pH 4, both in the (a) presence and (b) absence of 10 mmol L–1 Ca(NO3)2. Values are averages of 1 to 10 replications. Error bars are standard deviations of the means.