This essay offers “material rhetoric” as a new addition to the usual list of categories used to describe rhetoric in the eighteenth century (neoclassical, belletristic, elocutionary, epistemological/psychological) by examining the material elements of treatises written by Joseph Priestley and Gilbert Austin. Those material elements—namely heat, passion, and impression—are tracked through Priestley and Austin's scientific writings, thereby positioning their particular strains of material rhetoric as legacies of philosophical chemistry.