PURPOSE: To control the concn. of a soln. of a gas in a liq. on the basis of physical property values proper to the soln. without carrying out high precision real-time measurement requiring correction at all times and to prepare a soln. of a slightly soluble gas at an arbitary prescribed concn. with high reproducibility in spite of no established method for performing high precision real-time measurement of the concn.

CONSTITUTION: When a soln. of a gas in a liq. is prepd., an excess amt. of the gas having a uniform concn. is brought into contact with a certain amt. of a solvent at a constant temp. and they are continuously mixed and stirred. The resulting soln. is allowed to attain to the equilibrium concn. in an equilibrium attaining time proper to the soln. and this concn. is maintained.