When the soft drink 7-Up first came out it was 'lithiated'. The soda used to include lithium citrate, which is now better known as a mood-stabilizing drug. Similar to how Coca-Cola famously used to contain cocaine, the makers of 7-Up were capitalizing on the popularity of "medicated" soft drinks at the time.
That's what inspired this experiment. The original 7-Up did not contain a chunk of metal lithium but the end result is entertaining. The solution even ends up working as an indicator, changing from colorful to clear and back again depending on the acidity of the solution.