Per Teodor Cleve (10 February 1840 – 18 June 1905) was a Swedish chemist, biologist, mineralogist and oceanographer. He is best known for his discovery of the chemical elements holmium and thulium.
Cleve's first work was Några ammoniakaliska chromföreningar (Some compounds of ammonia and chromium, 1861). While in Paris, he visited the laboratory of Charles-Adolphe Wurtz and also made a number of friends there. While removing impurities from a sample of erbium oxide, Cleve discovered a brown substance and a green substance, and the brown substance was holmium oxide (the green substance was thulium oxide). However, this sample may have been impure. He separated thulium from an erbium oxide sample in 1879. Additionally, Cleve and Abraham Langlet discovered helium in the mineral cleveite in 1895.
Cleve discovered six forms of dichloronaphthalene and discovered aminonaphthalenesulfonic acids, which are sometimes named after him. In 1890, Cleve began to mainly focus on the field of biology, mainly studying freshwater algae, diatoms, and plankton. With Johann Diedrich Möller he issued and distributed an exsiccata-like series of microscope slides under the title Diatoms edited by P. T. Cleve and J. D. Möller.
Cleve, in collaboration with
Otto Höglund<!-- Otto Magnus Höglund -->
prepared numerous previously-undiscovered salts of yttrium and erbium. The two also did work on the chemistry of the chemical elements thorium and lanthanum. By 1874, Cleve discovered that thorium was a quadrivalent element and also determined lanthanum to be trivalent. These findings were initially doubted by the scientific community. His son-in-law and grandson, Hans von Euler-Chelpin and Ulf von Euler, both won Nobel Prizes. The second daughter, Agnes Cleve-Jonand (born Agnes Elisabet Cleve) (1876-1951), was a visual artist and pioneer of Modernism in Sweden. The third and last daughter, Célie Brunius (born Gerda Cecilia Afrodite Cleve) (1882-1980), was a journalist. His daughter Agnes was married to illustrator, set designer and artist John Jon-And. His daughter Célie was married to writer August Brunius and was the mother of artist Göran Brunius, journalist Clas Brunius and associate professor Teddy Brunius. The television host and politician Lisette Schulman was his great-granddaughter.
Per Teodore Cleve was a supporter of women's equality and Ellen Fries, the first Swedish woman to receive a PhD, was one of his students.