Interesting experiments were made in his classes. Both he and his student- assistants worked long hours in preparing the demonstrations so that all would go well.1

At the University Mendeleyev taught classes in the morning. In the afternoon he made experiments in his two-room laboratory. At night Mendeleyev spent much of his time working with the cards on which he put down information about each of the chemical elements.

Mendeleyev made thousands of experiments with his own hands. He made thousands of calculations, wrote a lot of letters, studied many reports. Everything in the world that was known about the chemical elements Mendeleyev knew. For months, for years he searched for missing data All those data were being brought together and grouped in a special way. In 1869 the description of more than 60 elements was completed, and Mendeleyev published his Periodic Table.

The Periodic Table is spoken of as the beginning of a new era in chemical thought.