At the right is a light source with a narrow slit in the nickel-plated shield. The light is focused on the entrance slit of the spectrometer at the left by the lens. Rock salt, placed in the middle section, is disassociated by the three gas burners. The exit side of the spectrometer swings from side to side to observe the spectrum and note the two black sodium D absorption lines in the otherwise continuous spectrum. 

   This apparatus is in the Greenslade Collection, and was in very poor shape when I received it. The salt had absorbed moisture and brine had dripped down over the apparatus, producing thick scales of rust. The rust was removed mechanically and the apparatus given a coat of wax to preserve it.