FIGURE 14 PREPARATION and some ELECTRICAL PROPERTIES of an FeS MEMBRANE (cf. Figs 6, 7a)
Ten millimoles of Na2S (representing the alkaline seepage water) is added to a 4% sodium silicate solution (representing the hydrothermal mound), gelled at pH 10 by addition of BIORAD in a tube, inverted and presented to 10 millimoles of FeSO4 (pH 4.2 representing the acidulous ocean). As to be expected from a reading of Figure 7, a tension of about 600 millivolts is recorded. Nevertheless, in this preliminary experiment, carried out at STP, Fe3+ rather than kinetically stable SO42-, is the likely electron acceptor. Thus the half-reactions are presumed to be:
i) 2HS- -> H2 + S2 + 2e-
ii) 2e- + 2Fe3+ -> 2Fe2+
If so, the membrane acts as the salt bridge (cf. Beutner 1920). In the absence of hydrosulfide the silica gel gives rise to an EMF of between 100 and 250 millivolts, a partial response to the pH contrast of nearly 6 units, though it decays more rapidly. These experiments have yet to be run in oxygen-absent conditions.
