The invention also relates to an apparatus for carrying out the process for accurately controlling the content of alumina, comprising means for delivering to each opening successive amounts of alumina, of substantially constant weight, means for measuring the internal pseudo resistance, means for calculating {HEAD ~ the speed} of {TAIL ~ variation} of the internal resistance, means for varying the rate of introduction of the amounts of alumina in dependence on the variations in the internal resistance, and means for varying the anode cathode distance of the tank 
The invention also relates to an apparatus for carrying out the process for accurately controlling the content of alumina , comprising means for delivering to each opening successive amounts of alumina , of substantially constant weight , means for measuring the internal pseudo resistance , means for calculating { HEAD ~ the speed } of { TAIL ~ variation } of the internal resistance , means for varying the rate of introduction of the amounts of alumina in dependence on the variations in the internal resistance , and means for varying the anode cathode distance of the tank
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