In 1927 Aston obtained, through mass spectrometry, the value 1.00778 for the atomic mass of hydrogen. At the time, the agreement of this number with that obtained by chemists was thought to be enough not to think of any other hydrogen isotope. However, in 1929, it was put forward that the oxygen had three different isotopes with mass numbers 16, 17 and 18. Subsequent corrections to the atomic mass of oxygen induced some ajustments in that of hydrogen, obtained by chemical processes. A slight increase of this value made the scientists to think of a new isotope of mass number 2 and atomic mass 2.0147 with a 1 to 5000 proportion.
Urey tried then to perform the separation of this isotope by fractionation of liquid hydrogen. The spectral analysis of the fractionation residue of huge amounts of hydrogen, revealed the existence of deuterium. Later, G. N. Lewis was able to isolate 1 ml of the so-called heavy water (D2O). The physical properties of this water were slightly different from ordinary water.
Nowadays, deuterium has several aplications such as in NMR (Nuclear Magnetic Resonance Spectroscopy) or in the nuclear fusion process.