Replacing gas in a chamber
Chemists who need to control which gases are in their vessels (e.g. those who work with air sensitive compounds) do this routinely.

There are two ways to achieve gas replacement. The more reliable way is to work with vacuum-lines that allow switching the input to a vessel between a vacuum and an inert gas. First the air is removed and then the inert gas introduced.

Often, though, this is overkill. In many cases where liquids are involved the liquid needs to be degassed (to remove air dissolved in the liquid). In many cases it is good enough to bubble the inert gas through the liquid and the vessel for long enough to sweep out the unwanted gases. Bubbling the inert gas through the liquid and allowing it to escape the vessel is good enough if done for long enough. 

If it isn't important to remove all traces of the original gas, this is usually an effective technique and gets more effective the longer the inert gas is allowed to flow.