Mendeleev resigned from Saint Petersburg University in 1890.
He left the university on 17 August 1890, after decades of teaching and research there. Mendeleev had joined the institution in the 1860s, became a professor, and helped turn its chemistry program into an internationally recognized center of research. His university career overlapped with the period in which he developed and promoted the periodic law.
The resignation followed a dispute with officials in the Ministry of Education over the treatment of university students. It was therefore not simply a routine retirement or a move caused by old age. After leaving the university, Mendeleev continued working on industrial, agricultural, petroleum, metrology, and other scientific questions.
The year is sometimes confused with 1893, when he became director of the Main Chamber of Weights and Measures. Nor was 1905 the departure date: that was the year he received the Copley Medal from the Royal Society. His university resignation belongs specifically to 1890.