The spectroscope magnified the spectrum to allow it to be studied in detail.
When Bunsen and Kirchhoff placed different salts in the flame of the recently invented Bunsen burner, they saw colored lines in each of the spectra they took.
Elemental rubidium is highly reactive, with properties similar to those of other alkali metals, including rapid oxidation in air.
On Earth, natural rubidium comprises two isotopes: 72% is the stable isotope, Rb, with a half-life of 49 billion years—more than three times longer than the estimated age of the universe.
Rubidium is a silvery-white and very soft metal — and one of the most highly reactive elements on the periodic table.
Rubidium has a density about one and a half times that of water and is solid at room temperature, although the metal will melt if it's just a bit warmer, according to Chemicool.
However, rubidium ions have the same charge as potassium ions, and are actively taken up and treated by animal cells in similar ways.