Sodium Absorption Lines

Burning of sodium bicarbonate in Bunsen flame produces sodium absorption lines in continuous spectrum. Sodium 'D' line absorption shows up as a black line in the yellow of a continuous spectrum. Good as a simulation of the sodium portion of the Fraunhoffer absorption spectrum caused by atoms in the solar atmosphere; it does not however, resolve the 5890/5896 doublet.

For more details, see
http://sciencedemonstrations.fas.harvard.edu/presentations/sodium-absorption