Friedrich Wilhelm Ostwald (September 2, 1853 - April 4, 1932)) was a German chemist. He received the Nobel Prize in Chemistry in 1909 for his work on catalysis, chemical equilibria and reaction velocities. Wilhelm Ostwald is usually credited with inventing the Ostwald process used in the manufacture of nitric acid. He did work on dilution theory leading to his discovery of the law of dilution which is named after him. Ostwald's rule concerns the behavior of polymorphs. He was an amateur painter who made his own pigments, and developed a strong interest in color theory in the later decades of his life. He was also interested in the international language movement, first learning Esperanto, then later supporting Ido. He died in a hospital in Leipzig in 1932 at the age of 78. He is considered one of the modern founders of the field of physical chemistry.