the statement that the total pressure of a mixture of gases is equal to the sum of the partial pressures of the individual component gases. The partial pressure is the pressure that each gas would exert if it alone occupied the volume of the mixture at the same temperature.

This empirical relation was stated by the English chemist John Dalton (Dalton, John) in 1801. It follows from the kinetic theory of gases under the assumption of a perfect (ideal) gas and assumes no chemical interaction between the component gases. It is approximately valid for real gases at sufficiently low pressures and high temperatures.