During the 19th century atomism was a controversial issue in chemistry. It is an oversimplification to dismiss the critics' arguments as all falling under the general positivist view that what can't be seen can't be. The more interesting lines of argument either questioned whether any coherent notion of an atom had ever been formulated or questioned whether atoms were ever really given any explanatory role. At what point, and for what reasons, did atomistic hypotheses begin to explain anything in chemistry? (...) It is argued that 19th-century atomic accounts of constant proportions and isomerism had little to offer, whereas a non-atomic explanation of chemical combination was developed. Not until the turn of the century did atomism begin to do serious explanatory work in chemistry. (shrink)