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Wikipedia's[2][3] Dmitri Mendeleev article states it plainly: "On 6 March 1869, he made a formal presentation to the Russian Chemical Society, titled The Dependence between the Properties of the Atomic Weights of the Elements". Russia was still on the Julian calendar, so contemporary Russian sources date the work to February; the manuscript sheet on Commons is signed 17.02.1869, the Julian date for 1 March, and the pin uses the Gregorian date Wikipedia gives for the presentation itself.
Carries the date and the title of the presentation to the Russian Chemical Society, and the description of a table ordered by atomic weight and valence.[1]
Sets the 1869 table in context - "The first periodic table to become generally accepted was that of the Russian chemist Dmitri Mendeleev in 1869" - and records the Julian dates around it (17 February 1869, 1 March in the Gregorian calendar) and the printed table appearing in May 1869.[1]
The RSC's interactive table, for the modern form of what Mendeleev proposed; institutional context, not a source for the date.
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