A little pump called the “Fizz Keeper” is available in kitchen supply stores to pressurize previously opened soft drink bottles and prevent loss of carbonation. The idea appears to make sense, but actually, the device does not work. Pumping the bottle can restore the pressure above the solution so the bottle feels hard, just like when it was purchased. But the manufacturers are unaware of Henry’s Law.
William Henry was an English chemist (1775-1836) who noted that the solubility of a gas in a liquid is proportional to the pressure of the gas over the solution. Other gases above the solution do not matter. Consider a carbonated beverage. Before the bottle is sealed it is pressurized with a mixture of air and carbon dioxide. The partial pressure of the carbon dioxide is very high, far higher than atmospheric pressure, so that a great deal of carbon dioxide dissolves. When the bottle is opened, the pressurized gas escapes and now the only carbon dioxide sitting over the liquid is the atmospheric carbon dioxide which has a tiny partial pressure of 0.0003 atmospheres. The excess carbon dioxide comes out of solution, producing the fizz. Once the bottle has been opened, the only way loss of dissolved carbon dioxide can be prevented is by pressurizing with carbon dioxide, not air.
