Atoms and weights;
His Karlsruhe Congress talk
Proves instrumental as
Step towards resolving
The 29 April 2020 Twitter poem focused on Stanislao Cannizzaro (1826-1910) and his role in clarifying atomic weight, a key concept for chemists, at the Karlsruhe Congress.
“Clearly, convincingly, /
S. Cannizzaro /
Considers delib’rately /
Atoms and weights…”
The Karlsruhe Congress, held in 1860, was the first international meeting of chemists. Scientists from several nations discussed the need to more systematically consider questions of nomenclature (naming compounds), chemical notation (representing compounds’ chemical make-up, structural arrangement, etc.), and atomic weight (quantifying elements’ weights relative to one another). Prior to Karlsruhe, different groups of chemists used different notations and reference schemes, and communication between groups often presented a significant challenge.
Of particular note, a paper from Stanislao Cannizzaro, written originally for his students, was distributed at this meeting; it drew a distinction between weights of atoms and weights of molecules, building on the work of Amedeo Avogadro. For many attendees, this paper and its presentation resolved several important questions.
“His Karlsruhe Congress talk /
Proves instrumental as /
Step towards resolving /
Two attendees at the Karlsruhe meeting were Julius Lothar Meyer (1830-1895) and Dmitri Mendeleev (1834-1907). Both of them were inspired by the standardization of atomic weight made possible by Cannizarro’s statements. Further, each was a chemistry teacher and used this idea in writing a new textbook for his students, organizing the elements into a table based on atomic weight; thus, Cannizzaro’s talks and paper “prove[d] instrumental.”
While both scientists were key figures in the development of periodic law, a publication by Mendeleev in 1869 is most commonly cited as the first version of the modern periodic table of the elements (PTE).
The last few lines here use “periodic debate” both to describe an academic discussion of periodic law and to emphasize the iterative nature of scientific discussions.