In this installment from physics professor and my dad, Dean Zollman, we find several advances in chemistry in the 19th century – as well as leaders in the field who refused to accept atomic structure despite the evidence. – Kim
By Dean Zollman
As we discussed last time, John Dalton (1766-1844) made real progress in explaining some chemical reactions in terms of atoms. Following on his work, several scientists advanced our knowledge of how elements blend to form new substances.
Joseph-Louis Gay-Lussac (1778-1850) showed the importance of thinking in terms of volumes of gases when considering how they combined. For example, he noted that two volumes of hydrogen and one volume of oxygen mixed to make two volumes of steam. Amedio Avogadro (1776-1856) concluded that equal volumes of any gases contained equal numbers of particles. Thus, he came up with the number that many of us were required to memorize in high school chemistry. Johan Jakob Brezelius created a notation for describing how elements combined. It is basically the notation that we use today. (This notation was one place where Dalton did not succeed; he had his own notation but Brezelius’ was less cumbersome and required less knowledge of the internal structure of molecules.) In addition, several laws and rules were created based on the way particles combined in chemical reactions.
With all of these “victories,” we would expect that the opponents of atoms would give up the battle. But scientists are people first. Biases die very slowly even in the face of strong evidence to the contrary.
One of most outspoken opponents of the atomic structure of matter was Jean Baptiste Andre Dumas (1800-1884). An important issue was that the experiments did not clearly distinguish between atoms and molecules. Dumas and Justus Liebig (1803-1873) added to the confusion by creating two types of atoms – physical and chemical. Dumas explained this difference with an analogy.
I find in Lewis the story of a demon who abducts a young lady and who, hoping to win her good graces, pledges to obey her first three orders: “Show me” said she, “the most sincere of all lovers.” He compiled promptly. “Very well” she continued, “but show me an even more sincere lover.” The demon was taken aback. “What would have happened had the lady been under the control of he who can show us an atom, and then divide it in two? He would experience no qualm producing the most sincere lover, followed by a more sincere still.” Mr. Griffins failed to understand that I had carefully distinguished between atoms relative to physical forces and atoms relative to chemical forces; that is to say, indivisible masses for the former, and other indivisible masses for the latter. It is thus possible to divide with one type of force that which resists the other type. In the case of chlorine and hydrogen chemistry dissociated atoms that physics could not dissociate. … That sums it up.
In this passage, we see confusion about atoms and molecules. Any volume of hydrogen gas is made of hydrogen molecules, but each molecule contains two atoms. There is nothing else but hydrogen. However, each “particle” of hydrogen can be divided into two hydrogen atoms. (Each of these atoms can be further divided, but then they are no longer hydrogen; that story will come much later.) Dumas’ solution was to create some things that could be divided by chemical processes and other things that could be divided by physical processes.
Dumas and Liebig were leaders in chemistry in the first half of the 19th century. For much of their lives they were somewhat bitter rivals. Some of their criticisms of each other seem closer to name calling than intellectual discussion. At the same time, both contributed to progress in chemistry and developed students who became the next generation of chemists in Europe. Liebig was also an applied chemist who invented chemical fertilizer, baby formula (both liquid and powered), and powdered beef bouillon. Today his laboratory in Giessen, Germany, has been restored as a museum, and it is worth a visit if you are in that area.
Dumas continued to be a critic of atoms as the fundamental building block of matter. He felt that atoms were theoretical constructions which could not be confirmed by experiment. Because chemistry was an experimental science, it should stick to observation. Another quotation from Dumas sums his thoughts well:
What is left of the ambitious exploration we began into the realm atoms? Nothing firm it seems.
What does remain is the conviction that chemistry strays as always when it abandons experiments and decides to proceed through the unknown. … If I were the master, I would outlaw the word “atom” from science convinced as I am that it goes far beyond experiments.
Dumas was not “the master” but he was a very influential member of the French Academy of Science. And Paris was considered a center – by some the center – of chemistry research during the first half of the 19th century. So, the concept of atoms was having a difficult time becoming established. However, things would begin to change, and we will look at some progress next time.
Portraits via Wikimedia Commons in the public domain.
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.