Thulium is a bright silvery-gray metal that tarnishes in air slowly. It is a chemical element and has the atomic number of 69 and the chemical symbol Tm. It is an extremely soft metal and can be cut with a knife. It is an extremely rare element and is only found in trace amounts in the crust of the Earth. It is never found in its free form in nature, but is found in minute quantities in certain minerals. The most common minerals where it is found are gadolinite, monazite (the most important commercial source of this element), xenotime and euxenite. The largest reserves of this metal are found in China. Let’s find out who discovered this rare element.
Who discovered thulium?
Thulium was discovered in 1879 by the Swedish chemist Per Teodor Cleve. He was searching for impurities in the oxides of other rare earth elements. He began specifically looking at the element erbium because he discovered differing atomic weights of the samples he obtained. This led to the conclusion that his samples must contain other elements. After removing all the known contaminants from the erbium he was left with two previously undiscovered substances. One was a brown color and the other was a green. The brown substance was an oxide of the element holmium and was given the name holmia by Cleve. The green substance was also an oxide of a previously undiscovered element. He named this oxide thulia and the new element thulium.
The element was not isolated for many years and the first to obtain almost pure thulium was American scientist Theodore William Richards. He carried out 15,000 recrystalizations of the compound thulium bromate to obtain pure thulium! He did this to accurately measure the atomic weight of this element. He was awarded the Nobel Prize for this, and other similar work, in 1914. The first commercial method of obtaining high purity thulium was not developed until the 1950’s.