Abstract

In some views in the history, philosophy and social studies of chemistry, Joseph Priestley is at least as well-known and cited for his objections to the new chemistry and his promotion of his own late version of the theory of phlogiston, as for his early series of discoveries about types of air for which he had become famous. These citations are generally not associated with any detailed indications about his late work from 1788 onwards and his late phlogistic theory, of which there has not been a detailed study. This paper undertakes a detailed study of Priestley’s late work on water and related airs. He put forward a theory to support which his apparatus and initial substances would have needed to exclude impurities altogether. His theory did not take into account the solutions to the difficulties with the experiment which had been comprehensively understood and published by the phlogistian Cavendish several years previously, and with which the Lavoisians were in agreement. Priestley readily and fundamentally changed his interpretations of experiments in order to support the theory he currently favoured, and he was highly selective about replying about the criticisms of any opponent. This detailed analysis shows many divergences between his own practices and aspects of his objections to the new chemistry, which have implications for those stances in the secondary literature which do not question his objections. Accordingly, this study has implications concerning the nature of chemistry and other sciences, how they do progress and how they should progress.