(1) The oxidation velocity of sodium sulphite solution was observed when air is passed at various velocities. (2) It was found that the oxidation velocities are independent of the concentration of sodium sulphite and the velocity constant was expressed as a linear function of the velocity of air passed. (3) The dissolution velocity of oxygen into water when the concentration of oxygen in the surface layer is kept zero, was calculated from the obserbed reaction velocity, and it was found to be expressed as a linear function of the velocity of air passed. (4) An interpretation of the mechanism of this reaction under the observed conditions was given. (5) The maximum value of the ratio of the total number of molecules of oxygen which enter into water to the total number of molecules of oxygen which collide with the unit boundary surface per unit of time at 25°C. was calculated from the observed results.