Control of alumina content during igneous electrolysis

Claim 1

IN THE PROCESS OF CONTROLLING THE ALUMINA CONTENT OF AN IGNEOUS ELECTROLYSIS BATH DURING THE MANUFACTURE OF ALUMINUM, THE STEPS COMPRISING PROVIDING A PILOT ANODE, THE BASE OF SAID ANODE HAVING A SMALL AREA RELATIVE TO THE TOTAL ANODE SURFACE IN SAID BATH, CAUSING A CURRENT IMPULSE TO PASS THROUGH SAID PILOT ANODE, THE CURRENT IMPULSE BEING SUCH THAT SAID BASE IS TRAVERSED BY A CURRENT HAVING A DENSITY HIGHER THAN THE DENSITY D OF THE CURRENT PASSING THROUGH THE ANODE SURFACE OF THE TANK UNDER NORMAL OPERATING CONDITIONS, SAID HIGHER DENSITY BEING BETWEEN 1.5 AND 10 TIMES THE DENSITY AND BETWEEN 1.0 AND 10 A./CM.2, MEASURING THE VOLLTAGE OF THE PILOT ANODE DURING THE DURATION OF THIS CURRENT IMPULSE, REPEATING THE IMPULSE SYSEMATICALLY UNTIL THE VOLTAGE OF THE PILOT ANODE EXCEEDS AN EXCESS VOLTAGE WHICH IS HIGHER THAN THE MAXIMUM VALUE OBSERVED DURING THE PRECEDING IMPULSES, WHEREBY THE MOMENT WHEN THE DISSOLVED ALUMINA CONTENT OF THE BATH HAS DROPPED BELOW A THRESHHOLD VALUE IS DETECTED, SAID THRESHOLD VALUE DEPENDING ON THE CHOSEN IMPULSE DENSITY.