Happy #NationalBunsenBurnerDay! These little burners represent rubidium, one of the two elements discovered by Robert Bunsen and Gustav Kirchhoff in 1861.
Bunsen developed his burner with assistant Peter Desaga to give a clean flame and used it in the spectroscope that he and Kirchhoff designed. They wished to study the emission spectra of elements and in doing so kicked off a new phase of element discovery. They first identified caesium, named for the deep blue line in its spectrum, and then rubidium, named for its characteristic dark red line. William Crookes followed with thallium (leafy green) and indium (indigo blue). Paul Émile Lecoq de Boisbaudran adapted the technique to discover gallium.
Ultimately Bunsen & Kirchhoff’s invention led to the discovery of helium, with the spectroscope used to analyse not an element heated in a Bunsen flame, but the flame of the sun.