When evacuated gas tubes were inserted into an electrical housing unit, the gas emitted a unique color.
The young girls viewed the different frequencies of light that each gas tube emitted. This light was viewed through a spectroscope.
After viewing the different colored gas through spectroscopes, the girls drew out the unique "bar codes" of emitted energy.
Different elements have different numbers of electrons. When these electrons fall from an excited state back down to a lower energy level, they emit different frequencies of light.
The girls from Dallas and Fort Worth learned a brief history of JJ Thompson, Robert Milliken, and Ernst Rutherford who all lead the way in our development in the structure of the atom. We now know that atoms have different energy configurations. Each configuration is associated with the energy required to hold it there. The girls observed how different elements create unique colors when the electrons in them are excited to higher energy levels. By viewing different elements in gas tubes with a spectroscope, they were able to draw out and identify different elements by their " bar code of energy emissions."