Method of producing phosphoric acid

Claim 1

A PROCESS FOR PRODUCING PHOSPHORIC ACID, WHICH COMPRISES THE STEPS OF: CONTINUOUSLY ADDING SULFURIC ACID AND PHOSPHATE ROCK TO A MIXING ZONE; CONTINUOUSLY REMOVING A SAMPLE OF THE MIXTURE RESULTING FROM THE REACTIONS IN SAID MIXING ZONE; FILTERING SAID SAMPLE TO REMOVE CRYSTALS THEREFROM, THEREBY PRODUCING A FILTRATE; DIRECTING SAID SAMPLE TO AN ANALYSIS ZONE; IN SAID ANALYSIS ZONE, DIRECTING A FIRST BEAM OF RADIATION THROUGH A LIQUID CONTAINING BARIUM IONS IN SOLUTION AND PRODUCING A FIRST SIGNAL WHICH IS A FUNCTION OF THE LIGHT TRANSMISSION THROUGH AID LIQUID; ADDING A PORTION OF SAID FILTRATE FROM THE FILTERED SAMPLE TO SAID BARIUM CONTAINING LIQUID A CONTROLLED CON/ STANT RATE, THEREBY FORMING A PRECIPITATE REPRESENTATIVE OF THE CONCENTRATION OF SULFURIC ACID IN SAID MIXTURE RESULTING FROM THE REACTION IN SAID MIXING ZONE; DIRECTING A SECOND BEAM OF RADIATION THROUGH THE RESULTING LIQUID CONTAINING SAID PRECIPITATE AND PRODUCING A SECOND SIGNAL WHICH IS A FUNCTION OF THE LIGHT TRANSMISSION THROUGH SAID LIQUID CONTAINING SAID PRECIPITATE; COMBINING SAID FIRST AND SECOND SIGNALS TO PRODUCE A THIRD SIGNAL WHICH IS A FUNCTION OF THE VARIATION BETWEEN SAID FIRST SIGNAL AND SAID SECOND SIGNAL AND THEREFORE A FUNCTION OF THE CONCENTRATION OF THE SULFURIC ACID IN SAID MIXTURE RESULTING FROM THE REACTIONS IN SAID MIXING ZONE; AND CONTROLLING THE RELATIVE RATES OF ADDITION OF SAID SULFURIC ACID AND SAID PHOSPHATE ROCK TO SAID MIXING ZONE RESPONSIVE TO SAID THIRD SIGNAL TO MAINTAIN SAID VARIATION CONSTANT AT A VALUE REPRESENTATIVE OF A DESIRED CONCENTRATION OF SULFURIC ACID IN SAID MIXTURE RESULTING FROM THE REACTION IN SAID MIXING ZONE