Dmitri Ivanovich Mendeleev (February 8, 1834 - February 2, 1907) was a Russian chemist, inventor and credited as being the creator of the first version of the periodic table of elements. Using the table, he predicted the properties of elements yet to be discovered. In 1863 there were 56 known elements with a new element being discovered at a rate of approximately one per year. After becoming a teacher, Mendeleev wrote the definitive textbook of his time: Principles of Chemistry (two volumes, 1868-70). As he attempted to classify the elements according to their chemical properties, he noticed patterns that led him to postulate his periodic table which described elements according to both atomic weight and valence. The Russian chemist and science historian Lev Chugaev has characterized him as "a chemist of genius, first-class physicist, a fruitful researcher in the fields of hydrodynamics, meteorology, geology, certain branches of chemical technology (explosives, petroleum, and fuels) and other disciplines adjacent to chemistry and physics, a thorough expert of chemical industry and industry in general, and an original thinker in the field of economy." He died in 1907 from influenza at the age of 72.