PURPOSE: To melt Au safely, exactly and easily by putting the Au into a sealed vessel resistant to chemicals and separately charging HNO3 and HCl under pressure to dissolve the Au by sudden reaction and intermittently and repeatedly discharging the dissolved solution.

CONSTITUTION: A filter cloth 6 of about 200W300 meshed is set in the cylindrical sealed vessel 5 made of "TEFLON ", the Au powder 2 of necessary amount is inserted and a sealing lid 7 is closed. Solenoid valves 12, 12' of pressure charging pipes 10, 10' are opened and metering pumps 11, 11' are operated for a fixed time to charge HCl and HNO3 from an HCl vessel 8 and an HNO3 vessel 9 under pressure and with fixed portions respectively. A reaction suddenly occurs and the Au is dissolved. By opening a valve 15 of a discharge pipe 16, this solution is discharged to a vacuum filter 14. The HCl and the HNO3 are again charged under pressure and with fixed portions to dissolve the Au and to discharge the solution into the filter 14. By intermittently repeating this operation, the Au can be dissolved in short time and in good operation efficiency without causing stagnation of the solution.