A periodic table found during a laboratory clear-out at the University of St Andrews is believed to be the oldest in the world.
Experts have dated the teaching chart as being printed between 1879 and 1886.
Work has been taking place to authenticate and preserve the fragile chart since it was found among old chemistry equipment in 2014.
Russian chemist and inventor Dmitri Mendeleev made his famous disclosure on periodicity in 1869.
The St Andrews chart bears an inscription identifying a scientific printer who operated in Vienna between 1875 and 1888.
Professor Eric Scerri, from the University of California, has dated the table to between 1879 and 1886.
Gallium and scandium, discovered in 1875 and 1879 respectively, are present but germanium, discovered in 1886, is not.
The university said no earlier lecture chart of the table appeared to exist.
Prof David O'Hagan, former head of chemistry at St Andrews, said: "The discovery of the world's oldest classroom periodic table at the University of St Andrews is remarkable.
"The table will be available for research and display at the university and we have a number of events planned in 2019, which has been designated international year of the periodic table by the United Nations, to coincide with the 150th anniversary of the table's creation by Dmitri Mendeleev."
The university was awarded a funding grant from the National Manuscripts Conservation Trust for the conservation of the chart.
A full-size facsimile is now on display in the School of Chemistry, while the original periodic table is being kept in climate-controlled conditions.