Graphite anodes used in caustic-chlorine electrolytic cells, and particularly cells of the so-called mercury type, must be relatively pure in respect to certain trace elements, particularly vanadium and others including chromium, molybdenum and tantalum. These elements, even in minute quantities in a cell in which sodium chloride is electrolyzed for the manufacture of chlorine and caustic, will cause an increase in hydrogen gas being produced.
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