Dalton's law of partial pressures
Dalton's law of partial pressures states that the total pressure (P) exerted by a mixture of gases is equal to the sum of the partial pressures (p) of the components of the gas mixture. The partial pressure is defined as the pressure the gas would exert if it was contained in the same volume as that occupied by the mixture. The law is named after the English chemist and physicist John Dalton. See also vapor pressure.