Jean Antoine Claude Chaptal was not only a chemical manufacturer and one of the first ‘industrial scientists’ but was also, according to his own testimony, one of the early supporters of Lavoisier's system of chemistry. It might be assumed that Chaptal's pioneering work in industrial chemistry was intimately linked with his acceptance of the oxygen system of chemistry; more specifically, that this theory served to direct and inform his applied research and contributed not a little to its success. Indeed, he himself in 1790 explicitly stated this to have been the case. A close study of his work prior to 1790 fails, however, to establish the importance of such a linkage. First, his selection of research topics proves to have owed little to the ‘new chemistry’ but much to the scientific and economic milieu of his province of Languedoc and of Montpellier, its administrative seat. Second, the significance of his acceptance of the ‘new chemistry’ appears rather problematic, not the least because of the rather hazy boundaries between the phlogistic and Lavoisian theories in the 1780s. Third, it is not clear from the evidence available how the new theory helped solve the various problems of industrial chemistry he faced, or could have done so, other than to offer alternative explanations for processes with which he was already familiar and indeed had often mastered. It will be suggested that it is precisely this less dramatic role which was filled by the new chemistry: that of ‘rectifying’ his ideas by providing alternative and more satisfactory rationalizations of his experiences and experiments in the laboratory and the factory, not that of enabling him to simplify and perfect old processes nor to invent new ones. To put the point more bluntly: Chaptal's early successes and reputation in industrial chemistry were not a by-product of his allegiance to the new chemistry; rather, his growing adherence to that system was a by-product of its ability to provide satisfactory post-hoc explanations of the chemical processes and products with which he was concerned.