Process for producing biuret

Claim 1

A PROCESS FOR THE PREPARATION OF BIURET FROM UREA, SAID BIURET BEING SUBSTANTIALLY FREE OF CYANURIC ACID, WHICH COMPRISES HEATING UREA AT ATMOSPHERIC PRESSURE TO ABOUT 140*C. TO FORM A MELT, SUBJECTING THE HEATED MELT TO A REDUCED PRESSURE OF ABOUT 140 TO 150 MM. OF MERCURY, RAISING THE TEMPERATURE OF SAID MELT OVER A PERIOD OF ABOUT 10 MINUTES TO ABOUT 150* TO 160*C. AND SIMULTANEOUSLY REDUCING THE PRESSURE TO BELOW ABOUT 75 MM. OF MERCURY TO FORM A CLEAR BIURET-CONTAINING REACTION MASS, HOLDING SAID MASS AT ABOUT 150* TO 160*C. AND A PRESSURE BELOW ABOUT 75 MM. OF MERCURY UNTIL THE INITIATION OF CLOUDING THEREIN, AND IMMEDIATELY THEREUPON DISCHARGING SAID MASS INTO AN AQUEOUS SOLUTION OF SODIUM HYDROXIDE, DISSOLVING SAID MASS THEREIN TO FORM A SOLUTION OF BIURET AND THE SODIUM SALT OF ANY BY-PRODUCE CYANURIC ACID PRESENT, COOLING SAID BIURET SOLUTION TO CAUSE SAID BIURET TO CRYSTALLIZE SELECTIVELY THEREFROM, AND RECOVERING AND WASHING AND DRYING SAID CRYSTALS TO PRODUCE BIURET SUBSTANTIALLY COMPLETELY FREE OF CYANURIC ACID AND SODIUM CYANURATE.