Redox-Conditions and Precipitation of Iron and Copper 

 6.2 6.6 70 7.4 78 8.2 8.6 9.0 9.4 pH 



191 



+ 500 +400 +300 +200 + 100 



100 



-200 mV 



Fig. 3. Redox-conditions before/after adding copper and iron salts to the 

 water (Aquarium no. 2/ marine). 



Marine Conditions (With Stirring) 



The pH value dropped from 7.1 to 6.8, Eh rose from —160 

 to + 500 mV. The heavy metals have been preeipitated within 

 three days at the surface of the mud in a dark-brown, loose 

 colloidal mud-water zone. After 12 days, normalization began 

 and the water again contained free H.S. Tlie border of the 

 upper oxydative and the lower reductive zone was about 1 cm 

 above the surface of the sediment, witli a Eh slnft of about 600 

 mV. About 31 days after the beginning of tlie experiment the 

 sulfuretum had been restored. The shifting of the potential had 



