Joseph Priestley was a prolific writer, producing more than 150 titles. He is perhaps best known for his work on the properties of different types of air. This book, building on a paper that earned him the Copley Medal, the oldest and most prestigious award of the Royal Society, explores eudiometry (a traditional method of calculating the composition of gaseous compounds) and introduces early ideas on photosynthesis. The most significant discovery made by Priestley during these experiments was oxygen, which Priestley named ‘dephlogisticated air’ and described extensively in the second volume of this work.