1. The oxidation velocity of stannous chloride in hydrochloric acid with air was studied. When the concentration of hydrochloric acid is smaller than about 0.25 normal, the reaction seems to be between first and zero order. When the concentration of hydrochloric acid is greater than about 0.25 normal, the velocity is independent of the concentration of stannous chloride. 2. The effect of temperature is small. 3. The dissolution velocity of oxygen into hydrochloric acid of various concentrations was obtained indirectly.