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Karlsruhe, general view, Baden, Germany, between 1890 and 1900, Detroit Photographic Company, 1905. (Library of Congress image via Wikimedia Commons, public domain)

In this installment on the history of atom theory, physics professor (and my dad) Dean Zollman discusses how the first international scientific conference was organized to discuss the various ideas about chemistry and resolve conflicting definitions. — Kim

By Dean Zollman

Dean ZollmanBy the middle of the 19th century, chemistry was in a state of disarray. Dalton, building on ideas developed by Lavoisier, seemed to have established that a model using atoms and molecules was the best way to understand chemical reactions. Avogadro and Ampere had added strength to these concepts with the conclusion that equal volumes of different gasses contained equal numbers of particles. Yet, well-respected researchers such as Dumas raised serious questions about the atomic hypothesis.

In addition, within the chemistry research and teaching community different definitions of fundamental terms such as “atom” and “molecule” created confusion. Likewise, no consensus had been reached on the makeup of many common substances.

Acetic acid formulas, 1861

Acetic acid formulas, 1861 (public domain image via Wikimedia Commons)

For example, J. Lothar Meyer (1830-1895) described the situation then as ” there was much confusion, every substance, even the simplest, had a series of formulas, e.g. water : H2O or HO or H2O2 … Even a simple compound such as vinegar could have enough proposed formulas to fill an entire page.” Meyer did not randomly select vinegar as one of his examples. In a textbook, Friedrich Kekulé (1829-1896) had included a table with 19 variations on the formula for acetic acid, the primary ingredient in vinegar.

This situation led Kekulé to propose that chemists needed to get together and work out some of these differences. He enlisted the aid of Carl Weltzien (1813-1870) and Charles Wurtz (1817-1884) to arrange the meeting. In 1859, Kekulé suggested that they organize an international conference of chemists in Karlsruhe, Germany, where Weltzien was a professor of chemistry. Karlsruhe was selected because it was considered a location that would be attractive to a large number of chemists and because the grand duke of the region, Frederick I (1826-1907) was a patron of the sciences. Thus, the location for the first international conference of scientists was chosen for the same reasons that many such conference locations have been chosen since then – an attractive location and someone who will help pay the bills.

In the spring 1860, Kekulé, Weltzien, and Wurtz composed an invitation which expressed the purpose of the conference. The purpose of the conference was stated as

Such an assembly cannot deliberate on behalf of everyone, nor can it pass resolutions by which everyone must abide, but by means of free and thorough discussion, certain misunderstandings could be eliminated, and common agreement facilitated on some of the following points: the definition of important chemical notions such as those expressed by the words atom, molecule, equivalent, atomic, basic: …

 The three organizers asked a large number of eminent chemists to sign the letter in hopes that their endorsement would encourage broad participation. Both Dumas and Liebig, whom we discussed last time, lent their names as did Louis Pasteur (as in pasteurization) and Robert Bunsen (known for the Bunsen burner). In total, 45 well-known chemists’ signatures were on the letter of invitation. (Things work somewhat similarly today. Instead of signatures on a letter of invitation, many international science conferences establish advisory committees which include people known in the field. This committee is publicized as helping organize the conference.)

A summary of the conference says that 140 chemists from throughout Europe attended. However, the list of participants contains only 126 names. (Wikipedia has a list of those attending.)

The conference was organized to assure that the important issues were discussed rather than individuals giving talks about their own research. (This factor is different than most international scientific conferences today.) A summary of the conference, written by Wurtz, indicates that the discussions were sometimes heated. However, after three days very little was resolved. The only direct vote was to allow continued use of a rather old set of formulas.

While the goals of the conference were not reached, several useful items did come out of the effort. A frequent contributor to the discussions was Stanislao Cannizzaro (1826-1910). In 1858, Cannizzaro had written a long letter which was later published as “A Sketch of a Course of Chemical Philosophy.” In this work he described his view on the importance of the hypotheses of Avogadro and Ampere. One of his concerns was that many mid-19th century chemists were not recognizing this importance. He also argued forcefully for making distinctions between atoms and molecules.

At the end of the conference Cannizzaro’s paper was distributed to all of the participants. Mary Jo Nye, a historian of science, states “[This paper] became central to chemistry in the late nineteenth century and especially to the revival of interest in Avogadro’s hypothesis of the relationship between gas volumes and numbers of gas molecules.” Thus, by providing a means to deliver Cannizzaro’s thoughts to a large number of chemists, the Karlsruhe conference helped provide progress in chemistry and the value of atomic models.

Among the Karlsruhe participants were Julius Lothar Meyer and Dmitri Mendeleev. Within a few years after the conference these chemists would create period tables which would bring much order to our understanding to the chemical elements and the atoms. Again the Karlsruhe gathering helped these people move forward on an important aspect of understanding elements, atoms, and molecules. We will look at that those developments next time.

A coincidence connects these events to my current status. Stanislao Cannizzaro was born in Palermo, Sicily in present-day Italy. From 1861 to 1871, he served as a professor of chemistry at the University of Palermo. Next week, the week of July 6, an international conference on the teaching of physics will occur at that university. By the time that this article is posted, I will be traveling to that conference.


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The Poetry of Atoms

Atom Theory in Ancient India

Religion, Science Clashed over Atoms

Medieval Arabic Scholarship Might Have Preserved Scientific Knowledge

Rediscovering a Roman Poet – and Atom Theory – Centuries Later

Reconciling Atom Theory with Religion

Did Atom Theory Play a Role in Galileo’s Trouble with the Inquisition?

Did Gifted Scientist’s Belief in Atoms Led to His Obscurity?

Does Atom Theory Apply to the Earthly and the Divine?

A Duchess Inspired by Atoms

Separating Atoms from Atheism

Isaac Newton: 300 Years Ahead of His Time

Issac Newton and the Philosopher’s Stone

When Chemistry and Physics Split

Redefining Elements

Mme Lavoisier: Partner in Science, Partner in Life

With Atoms, Proportionality and Simplicity Rule

Despite Evidence of Atoms, 19th Century Skeptics Didn’t Budge

Dean Zollman is university distinguished professor of physics at Kansas State University where he has been a faculty member for more than 40 years. During his career he has received four major awards — the American Association of Physics Teachers’ Oersted Medal (2014), the National Science Foundation Director’s Award for Distinguished Teacher Scholars (2004), the Carnegie Foundation for the Advancement of Teaching Doctoral University Professor of the Year (1996), and AAPT’s Robert A. Millikan Medal (1995). His present research concentrates on the teaching and learning of physics and on science teacher preparation.