Dalton's Law of Partial Pressure states that the total pressure exerted by a mixture of gases is equal to the sum of the partial pressure of individual gases. Dalton came up with the law of partial pressure from his work on the amount of water vapor that could be absorbed by air at different temperatures. It is fitting that this law is used most often to correct for the amount of water vapor picked up when a gas is collected by displacing water. Each of these gases, nitrogen, oxygen, carbon dioxide, in the air mixture have their own partial pressure. The three partial pressures of the three gases add up to the total atmospheric pressure.