SummaryHistorians have explored the continuities between science and the arts in the Industrial Revolution, with much recent historiography emphasizing the hybrid nature of the activities of men of science around 1800. Chemistry in particular displayed this sort of hybridity between the philosophical and practical because the materials under investigation were important across the research spectrum. Inflammable gases were an example of such hybrid objects: pneumatic chemists through the eighteenth century investigated them, and in the process created knowledge, processes and instruments (...) essential for the creation of a new gaslight industry from 1800. Once this industry began to expand and mature, the interests and experiments of the gas industry stimulated new research work which in turn had relevance for theoretical debates.This paper explores how the emergence of the gas industry from 1800 provided an impetus for new work in theoretical chemistry. Boulton & Watt, important pioneers of the gas industry, explored the compositions of inflammable gases for practical purposes: the composition of these gases had an important effect on the luminosity of gaslights, and hence the economics of the new technology compared to older forms of lighting. As they explored these questions in their engineering work, they stimulated their friend William Henry to explore the nature of these gases further, and he carried out a series of experiments to determine their composition more exactly than Boulton & Watt had done. Henry published a series of paper between 1805 and 1820 where he made arguments about the compositions of inflammable airs, and further related these to contemporary debates about the laws of multiple and definite proportions, as well as John Dalton's atomism. Henry's research was also a hybrid of the theoretical and practical in that he tried to develop results useful for the fledgling gas industry. Specifically, he suggested the best kind of coal to use, and showed how gas quality varied with distillation time and temperature. (shrink)