Nicholas W Best

Having refuted the phlogiston theory, Lavoisier uses this second portion of his essay to expound his new theory of combustion, based on the oxygen principle. He gives a mechanistic account of thermodynamic phenomena in terms of a subtle fluid (not yet named “caloric”) and its ability to penetrate porous bodies. He uses this hypothetical fluid to explain volume changes, heat capacity and latent heat. Beyond the three types of combustion that he distinguishes and defines, Lavoisier also explains other chemical sources of heat, such as the heat of solution.

Attempting to compare scientific theories requires a philosophical model of meaning. Yet different scientific theories have at times—particularly in early chemistry—pre-supposed disparate theories of meaning. When two theories of meaning are incommensurable, we must say that the scientific theories that rely upon them are meta-incommensurable. Meta-incommensurability is a more profound sceptical threat to science since, unlike first-order incommensurability, it implies complete incomparability.

This seminal paper, which marks a turning point of the chemical revolution, is presented for the first time in a complete English translation. In this first half Lavoisier undermines phlogiston chemistry by arguing that his French contemporaries (particularly P.-J. Macquer and Baumé) had replaced Stahl’s original theory with radically different systems that conceptualised the phlogiston principle in completely incompatible ways. He refutes their claims by showing that these later models were riddled with inconsistencies as to phlogiston’s weight, its ability to penetrate glass and its role as a source of colour and odour in chemical compounds.

Having refuted the phlogiston theory, Lavoisier uses this second portion of his essay to expound his new theory of combustion, based on the oxygen principle. He gives a mechanistic account of thermodynamic phenomena in terms of a subtle fluid (not yet named “caloric”) and its ability to penetrate porous bodies. He uses this hypothetical fluid to explain volume changes, heat capacity and latent heat. Beyond the three types of combustion that he distinguishes and defines, Lavoisier also explains other chemical sources of heat, such as the heat of solution.

The rapid theoretical changes that characterise the chemical revolution raise important philosophical questions. When the new chemistry introduced a radically different list of elements, rejecting the traditional Aristotelian division, even the concept of a chemical element was revised. This rupture allows philosophers to focus on the nature of chemical principles and highlights the boundaries of chemistry’s domain of enquiry. Assumptions that scientists are referring to the same real-world phenomena when describing different theoretical entities appear dubious considering Lavoisier’s refutation of phlogiston theory. Nevertheless, examining the relatively continuous progress of chemistry since the chemical revolution allows us to maintain a realist attitude toward chemical elements.