In his Sceptical Chymist (1661) Boyle attacked scholastic and alchemical matter theories through a critical evaluation of distillation practices, known as ‘fire analysis’. Boyle advanced a twofold critique of elements as primary constituents of matter – whether the four ancient elements, the three Paracelsian principles (tria prima: salt, sulfur, mercury), or combinations thereof, commonly identified with products of fractional distillation – and of ‘fire analysis’ as their ultimate experimental-empirical manifestation. Distillation, particularly of animal and plant matter, tended to produced five distinctive fractions that were associated with an elemental pentad consisting of the tria prima alongside earth and water, the two tangible ancient elements. The belief in the analytical power of fire was in part a vestige of notions rooted in antiquity and medieval/Renaissance iatrochemistry, which emphasized fire’s unique capacity to purify, perfect matter, and isolate its various essences. In principle, Boyle admitted only mechanistic explanations based on particles, motion, and the corpuscular textures. On an operative level, however, he employed “intermediate” and “subordinate” causes, qualities, and states such as heat, fluidity, fermentation, others. Distillation often provided a prime site for the empirical determination of such causes, whereby fluids/liquids were produced out of (mainly) liquids through the action of fire, itself a fluid-like agent in Boyle’s cosmology. Boyle’s intermediate-level operative epistemology was a liberating compromise that allowed him to stay committed to reductive mechanism at the micro-level while deriving conclusions from qualitative (and sometimes quantitative) observations at the macro- and cosmo-levels. The four elements were a fundamental part of this tripartite scheme, as was the conception and organization of substances along a spectrum spanning from solid-cold to fluid-hot. I will discuss some of the ramifications of these issues and their relation to distillation – the single most iconic practical tool in the arsenal of early modern chymists – and its increasingly controversial status in chymistry from Boyle onwards.

Fluids under fire: Robert Boyle on distillation, elements, and particles

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