BLACK, JOSEPH

born April 16, 1728, Bordeaux, Fr. died Nov. 10, 1799, Edinburgh, Scot. British chemist and physicist best known for the rediscovery of fixed air (carbon dioxide), the concept of latent heat, and the discovery of the bicarbonates. Black was born at Bordeaux, Fr., where his fathera native of Belfast but of Scottish descentwas engaged in the wine trade. He was educated at Belfast and in medicine and natural sciences at Glasgow University. There he had William Cullen (171290) for his instructor in chemistry, and the relation between the two soon became that of professor and assistant rather than of master and pupil. In 1751 Black transferred to Edinburgh to complete his medical studies. In 1756 he succeeded Cullen as lecturer in chemistry at the University of Glasgow and was also appointed professor of anatomy, though he exchanged that post for the chair of medicine. He practiced as a physician, as well. In his investigations of the heating of magnesia alba (magnesium carbonate), Black anticipated Lavoisier and modern chemistry by indicating the existence of a gas, carbon dioxide, distinct from common air. Black's account of his studies, published in 1756 as Experiments Upon Magnesia Alba, Quicklime, and Some Other Alcaline Substances, proved that the mild alkalies (carbonates) are causticized (become more alkaline) when they lose carbon dioxide and that absorption of this gas converts the caustic alkalies again to mild ones. Black found that carbon dioxide acts as an acid and is produced by fermentation, respiration, and the burning of charcoal, and he inferred its presence in the atmosphere. At the University of Glasgow, Black's studies ultimately led to his doctrine of latent heat. He noticed that when ice melts it takes up heat without undergoing any change of temperature, and he argued that this heat must have combined with the particles of ice and thus become latent. He verified this hypothesis quantitatively in 1761 and thereafter taught the doctrine. Although Black never published any detailed account of his work on latent heat, his friend James Watt doubtless was influenced by these ideas in his revolutionary construction of the condensing steam engine. Black also noticed that different bodies in equal masses require different amounts of heat to raise them to the same temperature, and so founded the theory of specific heats. Black's lectures were written out posthumously from his own notes, supplemented by those of his pupils, and published with a biographical preface by his friend and colleague John Robison in 1803 as Lectures on the Elements of Chemistry, Delivered in the University of Edinburgh. Additional reading William Ramsay, Life and Letters of Joseph Black (1918); A.L. Donovan, Philosophical Chemistry in the Scottish Enlightenment: The Doctrines and Discourses of William Cullen and Joseph Black (1975).