Dalton's law of partial pressures
      n : (chemistry and physics) law stating that the pressure
          exerted by a mixture of gases equals the sum of the
          partial pressures of the gases in the mixture; the
          pressure of a gas in a mixture equals the pressure it
          would exert if it occupied the same volume alone at the
          same temperature [syn: Dalton's law, {law of partial
          pressures]