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GERMANY Photosynthesis and corrosion in sea‐water. Amongst the causes of steel corrosion in sea‐water, the latter's oxygen content is of primary importance. Measurements made at the maritime laboratories at Biarritz have thrown light on the annual changes of the characteristics of sea‐water and have proved, in particular, the very considerable effect of oxygen dissolved in the sea‐water. This was produced, it was discovered, by the photcsynthesis of algae. The steel used in the experiments was a Siemens‐Martin steel of composition C 0.07, Si 0.03, Mn 0.36, S 0.019, P 0.013, Al 0.07%. The weight loss due to corrosion is directly proportional to the concentration of dissolved oxygen. If conditions are satisfactory oxygen concentration in sea‐water may be as high as 30 mg./ litre. This will occur, it has been found, in tidal backwaters during the outgoing tide, behind dams, or in natural shallows along the coastline.