History of the Pneumatic Trough

ALTHOUGH THE SOLID and liquid states of matter are the more tangible, it was the study of gases which laid the foundations for the Chemical Revolution. The contributions in pneumatic chemistry made by Torbern Bergman, Henry Cavendish, Karl Scheele, Joseph Priestley, and their contemporaries served to stimulate the studies of Lavoisier toward creation of the new chemistry. All of these studies became possible as a result of the development of an apparatus for the generation, collection, and manipulation of gases-the pneumatic trough. Despite the significance and simplicity of this device, its invention and improvement were fraught with major difficulties. Since the literature dealing with pneumatic chemistry contains a significant number of ambiguities and lacunae regarding the invention and development of the trough, it is the purpose of this paper to examine the sequence of contributions in order to clarify the picture. 1 Did the apparatus of Robert Boyle and John Mayow, for example, represent a kind of primitive trough, as is sometimes alleged ?2 Why did Stephen Hales develop the apparatus which we recognize as the pneumatic trough, and what were the motivations of other workers in developing their innovations? Was the substitution of mercury for water in the trough made by Cavendish or Priestley ?3 The element "air" was treated through the earlier centuries as a substance exemplifying the qualities of hot and wet in the ultimate degree. There was nothing to suggest that air might be a mixture of gases, and even had the suggestion been made, the tools of the day would have prevented any serious effort to divide atmospheric air into its several components. During the period of alchemy, covering more than one and a half millennia, air was looked upon as an elemental substance rather than simply a substance exemplifying the gaseous state of matter.