ScienceWeek

ON GASES

The early history of gases is related in some ways to the history of certain chemical operations and, in particular, to distillation. In distillation, a liquid is converted by heat into a vapor, the vapor then condenses in a receiver. However, in some operations, a chemical reaction would take place, and sometimes (our modern knowledge tells us) a gas would be produced. Operators did not understand this. Anything we would call a "gas" would be regarded as irrelevant, no more than a will-of-the-wisp. What concerned them most was the immediate practical consequence of any buildup of pressure in the system: the retort might explode. The apparatus would be damaged beyond repair, and the operator himself might well have been injured. Therefore, operators adopted the practice of making a hole near the receiver to allow any "spirits" to escape. This expedient saved the apparatus and allowed the distillation to be successfully concluded. What was lost seemed of no importance. As one later writer Sigaud de la Fond (1785) expressed it:

"Very far from suspecting what they might have gained from the work, they preferred to safeguard their apparatus. They were happier to abandon a product the value of which they did not understand than to risk losing the fruit of the different operations they were carrying out."

If 16th century "chemists" had been questioned about any possible loss, on reflection they might have spoken of a "spirit" or even a "wild spirit". This brings us to the famous definition of Jan Baptiste van Helmont (1579-1644): "I call this Spirit, unknown hitherto, by the new name of Gas, which can neither be contained by Vessels, nor reduced into a visible body..."

Adapted from: Maurice Crosland: "Slipper Substances: Some Practical and Conceptual Problems in the Understanding of Gases in the Pre-Lavoisier Era." In: F.L. Holmes and T.H. Levere (Eds.): Instruments and Experimentation in the History of Chemistry. MIT Press 2000, p.80. More information at: http://www.amazon.com/exec/obidos/ASIN/0262082829/scienceweek