  A number of chemists involved in the early advances of organic chemistry who did adopt atomism expressed their ontological commitment to ‘chemical atoms’. In doing so they distinguished their theories from those brands of physical atomism that were in the tradition of mechanical or Newtonian atomism and which sought to explain phenomena in general, and chemistry in particular, by reference to a few physical properties of atoms. Chemical atoms had more in common with natural minima insofar as they were presupposed to have properties characteristic of the substances they were atoms of. Chemical atomism lent itself to the idea that it was developments in chemistry that were to indicate which properties were to be attributed to chemical atoms, as exemplified in the path that led to the property ‘valency’. Alan Rocke (1984, 10–15 and 2013) interprets the use of formulae in organic chemistry as involving a chemical atomism that is weaker than physical atomism but stronger than a commitment only to laws of proportion.