Manufacture of fluoboric acid

Claim 1

A PROCESS FOR PRODUCING FLUOBORIC ACID COMPRISING MIXING A SLIGHT STOICHIOMETRIC EXCESS OF BORIC ACID WITH A WEAK FLUOSILICIC ACID SOLUTION WHICH CONSISTS OF AQUEOUS FLUOSILICIC ACID SOLUTION IN CONCENTRATION UP TO 20%. SLOWLY AND AT A TEMPERATURE OF AT LEAST ABOUT 70* C., TO PRODUCE FLUOBORIC ACID IN SOLUTION WITH A FILTERABLE PRECIPITATE OF SILICA AND WITH SOME FLUOSILICIC AND BORIC ACID REMAINING, AND THEREAFTER TREATING THE THEREBY ESTABLIDHED SOLUTION OF FLUOSILICIC ACID TO PRODUCE FURTHER FLUOBORIC ACID BY REACTION OF THE FLUOSILICIC AND BORIC ACID REMAINING IN SAID ESTABLISHED SOLUTION, BY CONCENTRATING SAID ESTABLISHED SOLUTION BY EVAPORATION WITH APPLICATION OF HEAT, SAID ESTABLISHED SOLUTION HAVING A CONCENTRATION OF FLUOBORIC AND FLUOSILICIC ACIDS COMBINED OF SUBSTANTIALLY LESS THAN 25%, AND SAID EVAPORATION BEING EFFECTED IN TWO STAGES AT SUCCESSIVELY INCREASING TEMPERATURES, THE FIRST STAGE BEING CARRIED TO A COMBINED ACIDS CONCENTRATION OF 25% TO 30% FOR REMOVING SILICA BY PRECIPITATION AND THE FINAL STAGE BEING CARRIED TO A COMBINED ACIDS CONCENTRATION OF 45% TO 50% FOR FURTHER REMOVAL OF SILICON IN VOLATILIZED COMBINED FORM.