In a recent essay review of William R. Newman, Atoms and Alchemy (2006), Ursula Klein defends her position that philosophically informed corpuscularian theories of matter contributed little to the growing knowledge of “reversible reactions” and robust chemical species in the early modern period. Newman responds here by providing further evidence that an experimental, scholastic tradition of alchemy extending well into the Middle Ages had already argued extensively for the persistence of ingredients during processes of “mixture” (e.g. chemical reactions), and that this corpuscular alchemical tradition bore important fruit in the work of early modern chymists such as Daniel Sennert and Robert Boyle.