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.1hasserved for almost 150 years as a key to discovering new elements and it has retained its key capacity until now.
2.His lectures were always listened to with great ...
3began to write a great text book of chemistry, known in its English translation as "Principles of Chemistry" Hard work preceded it.Mendeleyev made thousands of experiments and calculations, wrote a lot of letters, studied many reports.
4.All those data were being brought together ...
5earned him lasting international fame.
6were being brought together and grouped in a special way.
7serves as a basis for thousands of researches.
8.It is studied by philosophers, historians, teachers ...