1767, Priestley was offered a ministry in Leeds
located near a brewery. This abundant and convenient
source of "fixed air carbon dioxide from
fermentation sparked his lifetime investigation
into the chemistry of gases. He found a way to produce
artificially what occurred naturally in beer and
champagne, as well as in the baths of the fabled
resort of Spa in Belgium: water suffused with the
sparkling effervescence of carbon dioxide. The method
earned the Royal Society's coveted Copley Prize
and was the precursor of the modern soft-drink industry.
In the mid-18th century, the concept of an element
was still evolving. Researchers had distinguished no more than
two dozen or so elements, depending on who was doing the counting.
It wasn't clear how air fit into that system. Nobody knew what
it was, and researchers kept finding that it could be converted
into such a variety of forms that they routinely spoke of different
The principal method for altering the nature of air, early chemists
learned, was to heat or burn some compound in it. The second
half of the 1700s witnessed an explosion of interest in such
gases. The steam engine was in the process of transforming civilization,
and scientists of all types were fascinated with combustion
and the role of air in it.
British chemists were especially prolific. In 1754, Joseph Black
identified what he called "fixed air" (now known to be carbon
dioxide) because it could be returned, or fixed, into the sort
of solids from which it was produced. In 1766, a wealthy eccentric
named Henry Cavendish produced the highly flammable substance
Lavoisier would name hydrogen, from the Greek words for "water
Finally in 1772, Daniel Rutherford found that when he burned
material in a bell jar, then absorbed all the "fixed" air by
soaking it up with a substance called potash, a gas remained.
Rutherford dubbed it "noxious air" because it asphyxiated mice
placed in it. Today, we call it nitrogen.
But none of those revelations alone tells the whole story. The
next major discovery would come from a man whose early life
gave no indication that he would become one of the greatest
experimental chemists in history.