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Black, Joseph (b. April 16, 1728, Bodeaux, Fr.—d. Nov. 10, 1799, Edinburgh), chemist and physicist best known for the rediscovery of “fixed air” (carbon dioxide), the concept of latent heat, and the discovery of the bicarbonates. First educated in medicine and natural sciences at Glasgow University, in 1751 he transferred to Edinburgh to complete his medical studies. His thesis describes experiments in the heating of magnesia alba (magnesium carbonate) and anticipated Antoine-Laurent Lavoisier and modern chemistry by indicating the existence of a gas, carbon dioxide, distinct from common air, which he detected by using the balance. Carbon dioxide had been described first by Jan van Helmont (1577—1644) as gas sylvestre. Black’s fuller account published in 1756, 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.
Although Black made no detailed study of carbon dioxide, he had found that it acts as an acid, is produced by fermentation, respiration, and the burning of charcoal, and inferred its presence in the atmosphere.
In 1756 Black succeeded his first instructor in chemistry, William Cullen, as lecturer in chemistry at Glasgow, acquired the chair of medicine there, and also was a practicing physician.
His 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 in April 1762 he described his work to a literary society in Glasgow, he never published any detailed account of it, and others such as J.A. Deluc claimed credit for his results. 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. He also showed that equal additions or removals of heat produce equal variations of bulk in the liquid of thermometers.
Black published only two more papers. His 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 (1739—1809), in 1803, as Lectures on the Elements of Chemistry, Delivered in the University of Edinburgh.
