This thesis demonstrates how three chemists – Dmitrii Ivanovich Mendeleev, Julius Lothar Meyer, and John Newlands – emphasised different values when developing their systematisations of the chemical elements in 1863-1875. While no chemist emphasised just one value in the course of establishing of their systematisations, I argue that Newlands elevated simplicity (“simple relation”), Mendeleev completeness (polnost’), and Meyer carefulness when systematising the elements. This thesis sets to show that values provide an illuminating framework to articulate the differences among the competing periodic systems, and give us a novel reading of the priority dispute concerning the discovery of the periodic system.

By examining the role of values in the systematisation of the elements, this thesis seeks to give an example of an integrated history and philosophy of science (iHPS) approach to values. As integrating history and philosophy of science introduces some methodological challenges, I will start by arguing in favour the hermeneutic model to iHPS as articulated by Jutta Schickore (Ch.1). Chapters 2-5 are largely historical. Chapter 2 introduces historical background to the challenge of systematising the elements in the nineteenth century. I then demonstrate how Newlands (Ch.3), Meyer (Ch.4), and Mendeleev (Ch.5) emphasised different values in the course of developing their systematisations of the chemical elements. Chapters 6-8 are more philosophical. In chapter 6, I argue in favour of specific abstract characterisations of simplicity, completeness, and carefulness on the basis of the historical material presented in chapters 3-5. After arguing in favour of a specific understanding of values, I identify a distinct relationship between the chemists’ subsequent uses of the systems and their emphasis on specific values during the development of their systems. In particular, I argue that valuing of completeness contributed to Mendeleev’s use of the system for making predictions (Ch.7), whereas valuing of carefulness did much to support using Meyer’s system for error determination (Ch.8).