Karoliina Pulkkinen

This article focuses on the Russian chemist Dmitri Ivanovich Mendeleev's assessment of certain representations of various aspects of the periodic system that employed more mathematical methodology. The equations of interest were created by E. J. Mills, B. N. Chicherin, and J. H. Vincent. The English chemist Mills tried to find a firmer numerical basis for the periodicity of the elements. The Russian lawyer and political philosopher Chicherin was convinced of the existence of a mathematical law underlying the periodic system. The English physicist Vincent explored the connection between atomic weights and the elements' order in listings based on atomic weights—a project which he associated with the periodic system of elements. Although, for Mendeleev, the equations of Mills, Chicherin, and Vincent promised a more precise expression of the law of periodicity, he continued to invoke his earlier standards. In particular, Mendeleev wanted the equations to respect the individuality of the elements, and called for completeness in conveying the complexities of chemical phenomena. Thus, the very qualities that he had valued while developing his periodic system in 1869–1871 also characterised his evaluation of the new means of representing aspects of that system.

Much has been said about the accuracy of the famous predictions of the Russian chemist Dmitrii Ivanovich Mendeleev, but far less has been written on how he made his predictions. Here we offer an explanation on how Mendeleev used his periodic system to predict both physical and chemical properties of little-known and entirely unknown chemical elements. We argue that there seems to be compelling evidence in favour of Mendeleev genuinely relying on his periodic system in the course of issuing his predictions—a point recently contested by Woody Science after the practice turn in the philosophy, history, and social studies of science, Routledge, Abington, 2014). In particular, by using the known properties of a number of near neighbours of the three entirely unknown elements, we seek to show how the very format of his table enabled it to function as a powerful tool for Mendeleev in arriving at his predicted values. We suggest that Mendeleev’s use of the periodic system in making his prediction gives an illuminative example of what Woody calls “theoretical practices” in science.