Analyzer and method of control

Claim 1

APPARATUS FOR USE IN THE PRODUCTION OF PHOSPHORIC ACID AND FOR MAINTAINING THE SULFATE ION CONCENRTATION THEREOF WITHIN A PREDETERMINED RANGE, COMPRISING: A FIRST MIXING VESSEL; MEANS TO ADD PHOSPHATE ROCK TO SAID VESSEL; MEANS TO ADD SULFURIC ACID TO SAID VESSEL; MEANS TO WITHDRAW A SAMPLE STREAM FROM SAID VESSEL; ANALYZER MEANS TO MEASURE THE CONCENTRATION OF SULFATE IONS IN SAID REMOVED SAMPLE STREAM, SAID ANALYZER MEANS COMPRISING FIRST AND SECOND SAMPLE CELLS, MEANS TO DIRECT FIRST AND SECOND RADIATION BEAMS THROUGH SAID FIRST AND SECOND CELLS, RESPECTIVELY, A SECOND MIXING VESSEL, MEANS TO DIRECT A REAGENT THROUGH SAID FIRST CELL INTO SAID SECOND VESSEL, SAID REAGENT BEING A REGENT WHICH WILL REACT WITH SAID SULFATE IONS IN SAID SAMPLE STREAM AND CHANGE THE LIGHT TRANSMISSION PROPERTIES THEREOF, MEANS TO ADD AT LEAST A PORTION OF SAID REMOVED SAMPLE STREAM TO SAID SECOND VESSEL, MEANS TO DIRECT THE RESULTING MIXTURE OF SAID REAGENT AND SAID PORTION OF SAID SAMPLE STREAM FROM SAID SECOND VESSEL THROUGH SAID SECOND CELL, AND COMPARISON MEANS TO COMPARE THE RADIATION BEAMS TRANSMITTED THROUGH SAID FIRST AND SECOND CELLS; MEANS RESPONSIVE TO SAID COMPARISON MEANS TO CONTROL THE RELATIVE RATES OF ADDITION OF SAID SULFURIC ACID AND SAID PHOSPHATE ROCK TO SAID FIRST MIXING VESSEL; AND MEANS FOR RECOVERING PHOSPHORIC ACID PRODUCT HAVING A PREDETERMINED SULFATE ION CONCENTRATION.