Directions:

Halle (Saale) was the site where Dorn investigated radium emanation (radon). Commonly Dorn is credited with the discovery of radon, but this is incorrect; the true discoverer was Rutherford {LINK to Rutherford in Canada}.
Technisches Halloren- und Saline Museum, which outlines the history of the salt mines of the area, Mansfelder Straße 52 - N51 28.90 E11 57.57.
Original building of Friedrichs Universität, where Stahl (proponent of phlogiston) taught, now called the Neue Residenz; today the Neue Residenz holds to Geiseltal paleontological museum, Domstraße 5 - N51 28.99 E11 57.88.
Old Chemistry Building, where chemists including Vorländer and Ziegler worked; Mühlgasse -
N51 29.10 E11 57.85.
Old Physics Building, where Dorn performed his research on emanation from radium, Friedmann-Bach-Platz - N51 29.20 E11 57.88.
Leopoldina Society, holding historical information, Emil-Abderhalden-Straße 37 - N51 29.33 E11 58.22.
University Library, holding Dorn's dissertations, August-Bebel-Straße 13 - N51 29.40 E11 58.21.
"Portraits of Chemists" (including Stahl's) is at the Fachbereich Chemie (Department of Chemistry), Kurt-Motes-Straße 2 - N51 29.81 E11 56.56.