Variations on a theme : patterns of congruence and divergence among 18th century chemical affinity theories
The doctrine of affinity deserves to be recognised by historians of chemistry as the foundational basis of the discipline of chemistry as it was practiced in Britain during the 18th century. It attained this status through its crucial structural role in the pedagogy of the discipline. The importance of pedagogy and training in the practice of science is currently being reassessed by a number of historians, and my research contributes to this historiographical endeavour. My analysis of the variety of theories sheltered under the umbrella term ‘affinity theory’ has emphasised the role of pedagogy in influencing both the structure and the content of knowledge. I have shown that there were wide ranging discrepancies between many of the components of individual affinity theories. Nevertheless, the scope of divergence was limited. This underlying organisation resulted from the unifying hub of affinity theory, the logical common ground. This was the essence of the doctrine of affinity, encompassing the law of affinity and the conceptualisation of the table that brought together the relations described in the law. The doctrine of affinity thus provided a disciplinary common ground between chemists, providing a mediating level of understanding and communication for all those who subscribed to the doctrine of affinity, in spite of their detailed differences.