Oxygen and the lost world of giants

Oxygen, in its molecular form, is the second most abundant gas in our atmosphere but second to none in courting controversy. Its discovery is often credited to the great experimenter Joseph Priestley (1733–1904), who in 1774 showed that heating red calyx of mercury (mercuric oxide) in a glass vessel by focusing sunlight with a hand lens produced a colourless, tasteless, odourless gas. Mice placed in vessels of the new ‘air’ lived longer than normal and candles burned brighter than usual. As Priestley noted in 1775, ‘on the 8th of this month I procured a mouse, and put it into a glass vessel containing two ounce measures of the air from my mercuric calcinations. Had it been common air, a full-grown mouse, as this was, would have lived in it about quarter of an hour. In this air, however, my mouse lived a full half hour.’ Later experiments revealed that mice actually lived about five times longer in the ‘new air’ than normal air, giving Priestley an early indication that air is about 20% oxygen. About the same time, the Swedish chemist Carl Scheele (1742–86), working in Uppsala, showed that air contained a mixture of two gases, one promoting burning (oxygen) and one retarding it (nitrogen). Like Priestley, Scheele had prepared samples of the gas that encouraged burning (‘fire air’) by heating mercuric oxide, and also by reacting nitric acid with potash and distilling the residue with sulfuric acid. However, by the time his findings were published in a book entitled the Chemical treatise on air and fire in 1777, news of Priestley’s discovery had already spread throughout Europe and the great English chemist lay claim to priority. Only later did it become clear from surviving notes and records that Scheele had beaten Priestley to it, producing oxygen at least two years earlier. The harsh lesson from history, which still rings true today, is that capitalizing on a new exciting discovery requires its expedient communication to your peers. The talented Scheele died at 43, his life shortened by working for much of the time with deadly poisons like gaseous hydrogen cyanide in poorly ventilated conditions.