Joseph Black (1728-1799)

• produced "fixed air" (carbon dioxide) by chemical reaction in 1756
• first evidence of a gas as a distinct chemical species and not a modification of atmospheric air
• careful use of balance & weight changes

Carl Wilhelm Scheele (1742-1786)

• concluded that atmospheric air = foul air + fire air
• foul air (nitrogen) could not absorb phlogiston
• fire air (oxygen) had a strong attraction for phlogiston
• fire air results from 1771 or 1772 were not published until 1777
• heat = fire air + phlogiston

Priestley