An important skill for chemists is being able to identify an unknown chemical or mixture of chemicals. Modern chemists have a myriad of tools available to help them do this.  Much of modern chemical identification can be done in a "black box" way - inject a sample into a box, press start, and get your answer. We have instruments like IR Spectroscopy, GC-MS, and HPLC to help us determine what is present in a solution. Technology like we have today certainly wasn't available to early chemists, but they did have other fun chemical tests to help.

One of the earliest chemical tests was the flame test. It was known that a flame will burn different colors depending on the chemicals present long before we had the theory to explain it. When lithium is present, for example, a flame will burn bright red. Barium will burn green. To understand why we needed to first develop quantum mechanics. An electron is excited (its energy increases) by a flame. After staying in an excited state for some time the electron will eventually relax. When it does it releases a photon. The energy, and therefore color, of the photon depends on the element involved. This simple test can therefore tell us a great deal of information about what the chemical make-up of a solution is.

The modern application is, of course, fireworks. When fireworks are made they are stuffed with different chemical elements. Each element giving a distinct color. So tonight, when you see fireworks don't just say "Ooohh....Ahhhh" say "Oooohhh copper....Ahhh...sodium".

Here's a list of the chemicals used for fireworks:

Red: strontium or lithium salts
Orange: calcium salts
Gold: iron
Yellow: sodium sals
Green: barium salts
Blue: copper salts
Purple: mixture of strontium (red) and copper (blue) salts
White: magnesium or aluminum

And this great video about what makes fireworks "pop"