Thomas Kuhn discusses the Chemical Revolution in some detail in The Structure of Scientific Revolutions, that is, the great changes in chemistry ushered in by Lavoisier. In fact, Kuhn appeals to the discovery of oxygen as a means to elucidate his new theory of scientific discovery, a theory that has yet to leave a strong mark on the philosophy of science. Here, I aim to show that Kuhn’s theory of scientific discovery offers insight into understanding key discoveries of chemical elements in late 19th and early 20th century chemistry.
Image. Latest release of the Periodic Table (dated 4 May 2022), International Union of Pure and Applied Chemistry, https://iupac.org/what-we-do/periodic-table-of-elements/
Kuhn develops an original account of scientific discovery. His account of scientific discovery is intended to replace the popular view of discovery according to which a discovery is a “Eureka-like” experience in the mind of an individual scientist. For Kuhn, a discovery is a complex event that extends over time. Consequently, he claims it is not possible to identify an exact time of discovery, and, in many cases, it is not possible to identify a particular individual discoverer. Kuhn thus shifts the focus of discovery from inside the heads of scientists to the broader research context. This shift to scientific practice is in line with one of Kuhn’s other key conceptual innovations that has enriched our understanding of science, the “paradigm” concept. Paradigms also were invoked to emphasize the practice of science, and thus downplay the role of theory. Paradigms are learned in laboratory exercises, as part of the training of young scientists-to-be, and they facilitate the analogical reasoning and modeling that enables scientists to solve hitherto-unsolved research problems. This is the work of the typical normal scientist.
Kuhn’s theory of scientific discovery, it seems, can provide some useful insight when we consider the discovery of various chemical elements, especially in the period after 1860. This is the year of the famous Karlsruhe Congress, which brought together many of Europe’s greatest chemical researchers. It marks a point at which many chemists settled on organizing the chemical elements according to their atomic weight, partly as a result of a then-up-to-date list of atomic weights of various chemical elements circulated at the end of the Congress by the Italian chemist, Stanislao Cannizzaro.
The discovery of the noble gasses, for example, are a classical case of discovery that is illuminated by the framework Kuhn develops. Of course, there are isolated events in specific laboratories that occurred and that may, prima facie, appear to be discoveries of the various individual noble gasses. But the reception of these proclamations of discovery were not unproblematic. In fact, there was significant resistance in some quarters. Further, these elements took on a new significance when it was realized that they formed a coherent group, a group that could be set in a nice fashion at the end of the Periodic Table of Elements, the great accomplishment of mid- to late-19th Century chemistry. So, the discovery of the noble gasses is not, strictly speaking, a set of discoveries of individual elements, each creditable to an individual chemist and each occurring at a specific time and place. Rather, the discovery involves, also, the conceptualization that these specific elements form a family, the noble gasses (see Scerri 2020, 164-169). Arabatzis and Gavroglu (2016) have examined the discovery of the element Argon in great detail, thus supporting my general claim.
So, who discovered the noble gasses, and when did it occur? Well, a lot of chemists contributed to the discovery, and it occurred over a stretch of time between 1895 and 1900. Kuhn’s theory of scientific discovery seems useful here.
There is another sort of discovery in early 20th Century chemistry that is illuminated by Kuhn’s theory of scientific discovery. I have in mind here that “discovery” of various new “elements” that were made between, roughly, 1900 and 1914. Experimental techniques were refined considerably in the late 19thCentury. This led chemists to identify a number of new “elements” that would, in time, be reclassified as isotopes. Their initial discovery, though, was met with considerable enthusiasm, and some chemists of reputation did not hesitate to include them in the Periodic Tables of Elements that they published during this period of time. Now, one might be tempted to say the discovery of these elements occurred when they were isolated in the laboratory, and distinguished from other then-known elements. But this is an unsatisfactory characterization of what occurred for a number of reasons. The initial reports of some of these “elements” classified them as distinct, and hitherto unknown elements. But, strictly speaking, this misrepresents what they are, at least by current theoretical lights. Our current theory tells us that isotopes are variants of chemical elements that differ only in the number of neutrons they have, and some properties that are a consequence of this difference. With the discovery of isotopes, itself involving a rather complex discovery process, chemists came to regard some of these newly discovered elements as merely variants of already known elements. But this was only achieved once the notion of an isotope became an integral part of the chemical lexicon.
So, now some “elements” that appear to have been discovered between 1900 and 1914, are only properly understood sometime later, say by 1919 or so. Who discovered these elements and when? Again, it was not the chemist who first isolated them in the laboratory, and proclaimed the discovery of a new chemical element. That story is incomplete, and significantly misrepresents what we now believe happened. Kuhn’s theory of scientific discovery helps us make sense of these discoveries.
Ideally, philosophers of science and chemists will attend to Kuhn’s theory of discovery and then come to understand how complex scientific discovery is. It reminds us of the collective nature of scientific inquiry, and the fact that what we have achieved is a collective accomplishment, even if, in unreflective moments, we continue to associate discoveries with specific individual scientists .
* If you want to read Brad's thematically related article “Theodore Richards and the Discovery of Isotopes" click here: https://link.springer.com/article/10.1007/s10698-022-09449-4
Acknowledgments
I thank Lori Nash for critical feedback on an earlier draft. Eric Scerri’s wonderful book, The Periodic Table: Its Story and Its Significance, provides an insight account of the development of the Periodic Table, including the two episodes I discuss here. I thank Sarah Hijmans for helpful comments, and Vanessa Seifert for the invitation to write this piece.
References
Arabatzis, T., and K. Gavroglu. 2016. “From Discrepancy to Discovery: How Argon Became an Element,” in The Philosophy of Historical Case Studies, edited by T. Sauer and R. Scholl. Springer Nature, pages 203-222.
Scerri, E. 2020. The Periodic Table: Its Story and its Significance, 2nd edition. Oxford: Oxford University Press.