Joseph Priestley, FRS (13 March 1733 (O.S.) – 6 February 1804) was an 18th-century English theologian, Dissenting clergyman, natural philosopher, chemist, educator, and political theorist who published over 150 works. In “Experiments and Observations on Different Kinds of Air,” he reviews experiments with gases. A common theme in this work is measuring the volumes of gases held in glass tubes, and their increase or decrease when exposed to other substances. He also tests the effects of gases on mice, plants and insects. Priestley demonstrated that fixed air (now known as CO2) can be produced from several reactions including alcoholic fermentation, combustion and a mixture of oil of vitriol and chalk (sulfuric acid and calcium oxide). He also showed that it is soluble in water, and that its toxic effects can be reduced when agitated in water. In other experiments, he showed that combinations of gases can mix to form a smaller volume than the sum of both separate gases, as when he combi