Identify the graphite sample spectroscopically analyzed by Hermann Schüler in early 1940

Identify which specific graphite sample Hermann Schüler spectroscopically analyzed when reporting to Walther Bothe in early 1940 that boron could not be detected, in order to clarify the provenance of the impurity assessment used to interpret Siemens electrographite ash absorption measurements.

Background

In early 1940, Hermann Schüler at the Kaiser Wilhelm Institute for Physics informed Walther Bothe that spectroscopic measurements of a graphite sample showed calcium as the most prevalent impurity and no detectable boron. This assessment influenced Bothe’s interpretation of Siemens electrographite ash absorption in his 1941 diffusion experiment.

Later, Wilhelm Hanle reported measurable boron in Siemens electrographite, implying that the original spectroscopy-based assertion may have depended on the particular sample tested. The authors note that the specific sample analyzed by Schüler is not specified, leaving a gap in provenance that affects the historical evaluation of Bothe’s conclusion about graphite’s suitability.