In Dempster’s machine, an ion beam homogeneous in mass and energy but diverging from a slit could be brought to a direction focus.
This spectrometer was employed by Dempster to make accurate determinations of the abundances of the isotopes of magnesium, lithium, potassium, calcium, and zinc, laying the foundation for similar measurements of the isotopes of all the elements.
The name Frederick Soddy in 1913 for these different radioactive forms of the same chemical species, because they could be classified in the same place in the periodic table of the elements.
The ion of mass 22 was, in fact, a stable heavy isotope of neon.
At the connecting point between the two stages, the ions change charge from negative to positive by passing through a thin layer of matter ("stripping", either gas or a thin carbon foil).
Molecules will break apart in this stripping stage.
By varying the magnetic field, he was able to scan through a lines due to helium (mass 4), neon (mass 20), and argon (mass 40), there was a line corresponding to an ion of mass 22 that could not be attributed to any known gas.