determining the slope p, relative to the change in Ri as measured by step wherein p1 is compared to a reference value po 1 and if p1 <po 1, decreasing the distance between the anode and cathode and as soon as the internal resistance Ri exceeds Ro+r, increasing {TAIL ~ the rate} of introduction of {HEAD ~ alumina} for a time T to a rapid rate CR which is from 20 to 100% greater than the normal rate of consumption CN 
determining the slope p , relative to the change in Ri as measured by step wherein p1 is compared to a reference value po 1 and if p1 < po 1 , decreasing the distance between the anode and cathode and as soon as the internal resistance Ri exceeds Ro+r , increasing { TAIL ~ the rate } of introduction of { HEAD ~ alumina } for a time T to a rapid rate CR which is from 20 to 100 % greater than the normal rate of consumption CN
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