King's College London
Exhibitions & Conferences

Joseph Priestley’s discovery of oxygen

Fold-out plate showing equipment used by Joseph Priestley in his experimentsFold-out plate showing equipment used by Joseph Priestley in his experimentsThis section of the online exhibition is concerned with the first of a three-volume work Experiments and observations on different kinds of air by Joseph Priestley (1733-1804). In this work Priestley announced his discovery of several gases, including oxygen.

Prior to Priestley’s discovery, the theory that air was an elementary substance, formed some 2,500 years ago, still prevailed. Priestley found during a series of experiments that ‘air is not an elementary substance, but a composition’ of gases. One of the gases he discovered he called ‘dephlogisticated air’, which was soon after given the name ‘oxygen’ by the French chemist Antoine Lavoisier (1743-94), who recognised it as the active principle in the atmosphere. The discovery of the existence and activity of oxygen revolutionised chemistry.

The fold-out plate reproduced here shows equipment used by Priestley in his experiments. Using this equipment, he discovered oxygen, finding it to be a gas ‘of exalted nature’, observing that ‘a candle burned in this air with an amazing strength of flame’. In this work, as well as writing on his discovery of oxygen, Priestley identifies ammonia gas, nitrous oxide and nitrogen dioxide, along with the process of photosynthesis.

As well as being a scientific pioneer, Priestley harboured religious and political beliefs that were considered radical in his day. Priestley was a Dissenter (a Protestant not associated with the Church of England) who supported the American and French Revolutions. Many people found his opinions too radical, and in 1791 the Priestley Riots occurred in Birmingham on Bastille Day. A drunken mob damaged the Old and New Meeting Houses and destroyed Priestley’s house, Priestley and his family only just escaping with their lives. Priestley and his family emigrated to America in 1794, where he continued his scientific work until his death. The copy of Priestley’s work featured here contains the bookplate of his son, Joseph Priestley junior (1768-1863). The bookplate in this item is pictorial, not heraldic. It therefore belonged to Joseph Priestley junior, not his father, the chemist Joseph Priestley.


In this exhibition

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