Abstract
<jats:p>This chapter reconstructs Paneth’s work on the “chemistry of phantoms”: from his attempt to detect polonium hydride, he arrived in 1917/18 at the Vienna Radium Institute at the discovery of bismuth hydride. Using radioactive tracers, a gas stream, filter, ionization chamber, and electroscope, Paneth investigated volatile hydrides while confronting the central problem of distinguishing genuine gaseous compounds from mere radioactive contamination.</jats:p> <jats:p>A control experiment with thorium emanation and products of the thorium decay series provided the crucial evidence for BiH₃; the method was later extended to other metal hydrides, including tin hydride. The chapter also interprets Paneth’s approach as an example of serendipity and abductive reasoning in the sense of Charles S. Peirce, while polonium hydride itself remained a chemical “phantom.”</jats:p>