A rainbow of colors should be seen. Place, one at a time, a color filter in front of the light bulb and observe. Now use the gas discharge tubes with the power supply and look at the light through the diffraction grating. Write down what you see for each tube. Each of the tubes will be for a specific element.
Common tubes are hydrogen, helium, neon, mercury.
Tubes containing air, carbon dioxide, and water vapor are also available. It can be an audio CD or one containing computer software. Make sure it is old and not needed. Use a flashlight with a narrow beam and shine at an angle onto the CD in a dark room. Observe the reflected light on a white screen or white board.