In 1904, scientists were working to piece together the series of products as a radioactive atom disintegrates, and understand which elements are related by the process. At this time, Boltwood showed that old geological samples contain a constant ratio of radium and uranium, and he set out to prove the two are connected. To do so, he attempted to determine radiums parent element by "growing" it from uraniums known product, "uranium X". His attempts were unsuccessful, and he suspected a long half life would make it impossible to "grow" radium in a measurable amount. In 1907, he discovered a new element with a half life of almost 100,000 years before it decays to radium, and he named it "ionium" after the ionizing action of its alpha particles. Boltwood was able to prove that ionium disintegrates to radium, and the full connection to uranium was shown in work by Frederick Soddy in 1919. Once the existence of isotopes was established in 1914, Stefanie Horovitz and Otto Hönigschmid demonstrated that ionium was actually thorium-230, the second known case of an isotope, rather than its own distinct element. However, the work of these two scientists in Vienna, as they precisely measured the atomic weight of lead from radioactive sources, also served to reinforce Boltwood's assertion that lead is the final product in the uranium decay series.