"Observations on different kinds of air" were first published in the Philosophical Transactions in 1772. As the experiments themselves were performed at such a prolific rate, it was decided to publish them in book form. Three volumes entitled Experiments and Observations of different kind of Air were issued, followed by the continuation, Experiments and Observations relating to various Branches of Natural Philosophy, also in 3 volumes.

"Priestley's hundreds of experiments on different types of 'air' led to the identification of numerous gases, including ammonia, nitrogen dioxide and (most importantly) oxygen, which he obtained by heating mercuric oxide. Although the Swedish chemist Scheele had succeeded in isolating oxygen at least two years before Priestley, Priestley was long credited with the discovery of oxygen. As he was the first to publish his discovery. Priestley's experiments with gases led Cavendish and Watt to discover the compound nature of water, and it was his revelation, coupled with Priestley's isolation of oxygen, that formed the experimental basis of Lavoisier's new oxidation chemistry." (Norman)