A sodium lamp is arranged to shine on a rear projection screen. An ordinary flame, say of a match or Bunsen burner introduced between the lamp and the screen will not cast a shadow, but if a wire or stick dipped in salt solution is placed in the flame, a dark shadow of the flame appears.
Arc tubes of hydrogen, helium, argon, mercury, and a few others can be viewed three-at-a-time with a large holographic grating. Also available is an incandescent light which can be used to look at a continuous spectrum.
Another option is that students can use individual gratings to see spectral lines of these tubes.
A hollow prism filled with carbon disulphide will disperse white light into its component colors. Other glass and lucite prisms are available, but their dispersion is not as great as CS2.
The action of a diffraction grating itself can be demonstrated by passing a laser beam through the grating and showing the spread out spots on the wall. You can lead into the phenomenon by showing the effect of Single, Double, and Multiple Slits [1] with the Cornell plate. Interesting effects result from crossing two gratings in the laser beam, or by arranging many at all different angles.
The arrangement below will project the lines of mercury just above their positions in a continuous spectrum of a tungsten filament. By adjusting the height of the 45° mirror you can have the entire length of the mercury lines, mercury lines above continuous spectrum, or just the continuous spectrum. Note that the spectrum of the tungsten filament is deficient in blue as befits a 3000° black body which peaks in the infrared.
Reference instructions for assistant:
Links:
[1] https://demoweb.physics.ucla.edu/node/90