Dalton's Law

The third in a line of law’s that are used when diving, or are known to govern the effects of diving is Dalton’s law. John Dalton in 1801 put together the idea of how ideal gas pressure was related, basically how the pressure of a mixture of gases may be defined as a summation of each gas. Simply put, by Dalton is “The total pressure in a container is the sum of the partial pressures of all the gases in the container.”

Dalton studied the effect of particular gases when mixed together, this is known as Dalton’s law of partial pressures. Partial pressure is explained as the pressure of a single gas when the gas is the only one in a container. The Dalton law theory said that if there was a large amount of space between gases molecules in the mixture, the gas molecules had no influence on other gases, maintaining the pressure of the gas sample would be the same no matter it was the only gas present or it was among other gases. Therefore the idea that the molecules are alone works well if there is a sufficient amount of space between the gas molecules in the mixture and temperatures are not too low. Dalton’s law states that by lowering the temperature or compressing the gas, it will upset the assumption he spoke of. Though too many is may sound simple, but is possible one of the most useful of gas laws in real life.

Dalton’s law as it pertains to scuba divers is to see how if affects air at different pressures, for this it is assumed that a mixture of gas in a scuba tank is made up of nitrogen and oxygen with a ratio of 80% or 20%. These two numbers are referred to as partial pressures, meaning at the surface of the water the pressure on the diver by the nitrogen mixture is 11.76 pounds per square inch or psi, the pressure from the oxygen in the tank is 2.94psi, put together the gases account for the total of the 14.7 psi of pressure on the surface of the water, as it should be.

Some recreational diving may be done with a special moisture called nitrox, while most is done breathing plain air, Dalton’s law dealt with the physiology of diving and understanding the physics of gas mixtures how they can effect the contents of the tank and the diver.