See also: 7B11.65 in Astronomy.  NOTE: Make sure the liquid rare earth solutions are stored in an upright position to prevent leakage.  Some evaporation may occur over time.  In that case just add distilled water to the remaining solutions to replentish.

Position the slit slide on the overhead and place the holographic grating in the exit beam.  Place the desired rare earth over half of the slit.  In this fashion you will be able to see the regular spectrum and an absorption spectrum.

NOTE: The spectrum will be a molecular absorption (band absorption).

Holmium should have absorption lines at 415, 450, 535, and 640 nm, with half-widths of less than 5 nm.

The GE "Reveal" bulbs have a slight blue tint to them due to the neodymium added to the glass envelope.  Just place the glass of the bulb into the light path to see the spectrum.

Place the mask on the overhead and position the grating in the exit beam.  Place the didymium glass so that it covers one half of the slit.  In this fashion you will be able to see the regular spectrum and an absorption spectrum.

NOTE: The spectrum will be a molecular absorption (band absorption).

Didymium is a mixture of neodymium and praseodymium.

There should be 5 absorption lines at 430, 450, 530, 580, and 690 nm, with half-widths of about 10 nm.

The long spectrum tube apparatus shows a rainbow spectrum at the bottom with the two Reveal tube bulbs on the top which have some Neodymium in the glass envelope.  This will show that some portions of the yellow, orange, and green parts of the spectrum are missing from the top spectra.