According to popular legend, D. I. Mendeleev discovered his famous Periodic Law in a dream. Historians of science have long refuted this apocrypha, but they have never doubted the date of promulgation of the law - March 1, 1869. On this day, as Mendeleev himself wrote, he sent the first printed Table to “many chemists.” But was the scientist wrong? Was he wishful thinking? The famous historian Pyotr Druzhinin was the first to criticize the generally accepted data on the publication of the discovery. Relying on unknown archival documents and unrecorded sources, the author was able not only to re-build the chronology of the appearance of the original version of the Periodic Table in print, but also to accurately establish the date of the first publication of the Periodic Law - one of the fundamental laws of natural science.