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The Oesper Collections in the History of Chemistry, Apparatus Museum, University of Cincinnati
Evolution of the Pneumatic Trough

The pneumatic trough has no single inventor, but rather evolved over time. Already in the 17th century, Robert Boyle (1660) and John Mayow (1674) had established the practice of collecting various gases or "airs" via water displacment (figure 1). The gases in question (largely hydrogen) were chemically generated within the pneumatic trough itself using chemicals dissolved in the collecting water. In 1727 the English minister, Stephen Hales, proposed a trough in which the site of gas generation was outside or external to the trough (figure 2); in 1765 the English physician, William Brownrigg, proposed the addition of a shelf to support the collection bottles (figure 3); and in 1766, the English chemist, Henry Cavendish, proposed the use of mercury as the collecting fluid when dealing with gases that were highly soluble in water (figure 4). The final touch was Joseph Priestley's suggestion in 1774 that the collecting shelf should be submerged below the surface of the collecting liquid rather than resting on the rim of the trough as in Brownrigg's design.

Further Reading:
J. Parascandola, A. Ihde. "History of the Pneumatic Trough." Isis 60 (1969): 351-361. (View article online in JSTOR)


 
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