Rubidium (RB 85.2). This element was first discovered by Bunsen in 1861, the source being some mineral waters from Durkheim, and the method the application of spectroscopic analysis. By this means the presence of the metal could be detected in a few drops of the water, although many tons had to be used before sufficient could be obtained to experiment with. The metal closely resembles potassium, igniting if thrown upon water. Its salts also are very similar to those of potash. Although only existing in very small quantities, the metal is very widely distributed, being found in sea water, many mineral waters, sea-weeds, tobacco, tea, and many other plants, as well as associated with potassium in many minerals.