“All the experiments that have been hitherto carried out, and those that are still being daily performed, concur in proving that between different bodies, whether principles or compounds, there is an agreement, relation, affinity or attraction (if you will have it so), which disposes certain bodies to unite with one another, while with others they are unable to contract any union: it is this effect, whatever be its cause, which will help us to give a reason for all the phenomena furnished by chemistry, and to tie them together.”

“Despite the caution of Black and his followers, in the second half of the eighteenth century, there was a hardening of opinion in favor of the ‘material theory of heat’. The difficulties of the ‘kinetic theory’ which was favored by mathematicians and physicists were still unresolved, while the chemists who came increasingly to dominate the study were, perhaps by tradition (in the footsteps of Boerhaave), perhaps by metaphysical preference, predisposed to favor the substantial theory. An exception was Pierre Macquer, but he had few disciples.”

— Donald Cardwell (1971), From Watt to Clausius (pg. 57)