First Uses of the Periodic Table Element -Deuterium. The Early Days of Deuterium: Pioneering Uses and its Evolving Role. When it comes to hydrogen isotopes, most of us are familiar with protium, the lightest and most common form. However, there is another isotope, deuterium, that has played a significant role in scientific research and practical applications since its discovery in 1931. Its initial applications were groundbreaking, yet over time, deuterium was gradually replaced by more efficient alternatives. Let us delve into its early uses and explore the reasons behind its decline from those specific purposes.