Black Identifies Carbon Dioxide

Joseph Black showed that when intensely heated, magnesia alba (magnesium carbonate) and chalk (calcium carbonate) produced “fixed air,” a gas later called carbon dioxide with unique physical and chemical properties.

Summary of Event

For more than two thousand years alchemists considered air an element, but the Scottish chemist Joseph Black, by discovering that carbon dioxide was a different kind of “air,” made an important contribution to modern chemistry. His studies at the Universities of Glasgow and Edinburgh prepared him well for this discovery. At Glasgow, where he studied medicine, the lectures of William Cullen sparked his interest in chemistry, and it was at Edinburgh, where he received his medical degree in 1754, that he wrote his doctoral dissertation, marking the beginnings of his significant work in chemistry. [kw]Black Identifies Carbon Dioxide (June 5, 1755)
[kw]Dioxide, Black Identifies Carbon (June 5, 1755)
[kw]Carbon Dioxide, Black Identifies (June 5, 1755)
Carbon dioxide
Chemistry;carbon dioxide
[c]Chemistry;June 5, 1755: Black Identifies Carbon Dioxide[1430]
[c]Science and technology;June 5, 1755: Black Identifies Carbon Dioxide[1430]
[c]Health and medicine;June 5, 1755: Black Identifies Carbon Dioxide[1430]
Black, Joseph
Rutherford, Daniel
Cullen, William

This dissertation, De humore acido a cibis orto et magnesia alba (1754; On Acid Humor Arising from Foods, and on White Magnesia, On Acid Humor Arising from Foods, and on White Magnesia (Black) 1973), had its origin in Black’s desire to investigate magnesia alba’s ability to dissolve gall and kidney stones, but when he found it lacked this ability, he decided to study its effect on stomach acidity. He prepared magnesia alba (magnesium carbonate) by reacting Epsom salt (magnesium sulfate) with pearl ash (potassium carbonate). Although the first part of Black’s dissertation did examine the medical use of magnesia alba as an antacid, the second, more creative part of the work examined his own experiments on magnesia and some of magnesia’s chemical reactions.

In the two years before completing his dissertation, Black discovered that magnesia alba, when vigorously heated, produced a previously unknown compound, “calcined magnesia” (magnesium oxide), which weighed less than the magnesia alba with which he started. Similarly, when he heated chalk (calcium carbonate), the quicklime (calcium oxide) he produced weighed less than the chalk. He attributed the lost weight of the chalk and magnesia alba to a new “air” that was not the same as ordinary air. Since this air could be combined with (or “fixed into”) quicklime to form chalk, he called the gas “fixed air.” Fixed air (carbon dioxide) He showed that birds and small animals perished in fixed air, and that fixed air could extinguish a candle flame. Black also found that burning charcoal produced this gas, as did the respiration of humans and animals. Black even developed a specific reagent to test for fixed air. By dissolving quicklime in water, he made limewater, a reagent that turned cloudy in the presence of fixed air.

After solving the puzzle of magnesia alba’s and chalk’s weight loss on heating, Black investigated the other products of these reactions, quicklime and calcined magnesia, and the puzzling observation that when milk alkalis were added to these substances, they became caustic. The substances that Black called “mild alkalis” are today recognized as compounds such as potassium and sodium carbonate. For example, when Black reacted slaked lime (calcium hydroxide) with potash (potassium carbonate), he obtained chalk (calcium carbonate) and “caustic potash” (potassium hydroxide). Black was fascinated by what he called “caustication.” He knew that limestone (calcium carbonate) became caustic (in the form of quicklime) when it lost its fixed air, and he was able to explain why caustic alkalis became mild after standing for some time in air. The caustic alkali reacted with the fixed air in the atmosphere to form a mild alkali. Since, in these studies, Black carefully weighed both reactants and products, he was able to detail fixed air’s participation in a cycle of reactions.

Black made his first public presentation of his discoveries about fixed air on June 5, 1755, when he read his paper, “Experiments upon Magnesia Alba, Quicklime, and Some Other Alcaline Substances,” “Experiments upon Magnesia Alba, Quicklime, and Some Other Alcaline Substances” (Black)[Experiments upon Magnesia Alba, Quicklime, and Some Other Alcaline Substances] before the Physical, Literary, and Philosophical Society of Edinburgh. The paper was published in 1756 in volume 2 of Essays and Observations, Physical and Literary. Black’s principal findings were that fixed air was a unique gaseous chemical substance and that it was a measurable part of such alkaline materials as magnesia alba, limestone, potash, and soda (sodium carbonate). Black intended to follow this influential paper with further serious studies of fixed air, but his increasingly burdensome responsibilities at Glasgow and, after 1766, at Edinburgh interfered with his chemical research. Nevertheless, he turned over some of the problems raised by his fixed-air research to one of his students, Daniel Rutherford, who in 1772 discovered another new “air.” When Rutherford removed from ordinary air all the gases produced by either combustion (the burning of a candle) or respiration (the breathing of a mouse), what remained was a new gas he called “mephitic air” Mephitic air (nitrogen) because no animal could live in it. Mephitic air is now called nitrogen, and Rutherford is credited with its discovery.

Rutherford was not the only distinguished student of Black. In his thirty-three-year career at Edinburgh, Black taught students from all over the world, including France, Germany, the United States, and Russia. Many of his students went on to distinguished careers in medicine, chemistry, and physics. Although he was aware of the weaknesses of the phlogiston theory Phlogiston theory —which explained combustion, respiration, and other phenomena in terms of a “weightless fluid,” or substance, called phlogiston—Black did try to explain his experimental results in terms of its principles. However, late in his career, Black began to teach the new chemical ideas of the French chemist Antoine-Laurent Lavoisier, Lavoisier, Antoine-Laurent who had been deeply influenced by Black’s experiments on fixed air.


Traditional historians of science consider Joseph Black the founder of quantitative pneumatic chemistry because he reasoned on the basis of meticulously executed experiments to conclusions based on quantitative arguments. Using refined techniques of analysis and synthesis, Black falsified the old idea of a single elemental air and showed that a new gas could be created and that it could be combined chemically with a solid to produce a new compound. Once Black had established that fixed air was a unique chemical substance, other scientists, such as the English natural philosopher Joseph Priestley, Priestley, Joseph discovered many new gases, including oxygen, which in Lavoisier’s hands became the central element of the chemical revolution.

Some revisionist historians of science have questioned the classic characterization of Black as the great quantifier of chemistry, claiming that he emphasized microscale attractive forces rather than macroscale weight relationships as the key to understanding chemical phenomena. Other scholars consider Black’s significance to be his liberation of chemistry from traditionally allied disciplines such as medicine and metallurgy. Still other scholars see the importance of Black’s studies on carbon dioxide as the beginning of the breakdown of the barrier between animate and inanimate substances, because carbon dioxide was produced both by burning inanimate charcoal and by the respiration of animate mice. Because of his phlogistic views, Black is not categorized among the modern chemists, but his chemical discoveries greatly influenced the new chemical ideas of Priestley, Henry Cavendish, and Lavoisier.

Further Reading

  • Black, Joseph. On Acid Humor Arising from Foods, and on White Magnesia. Translated by Thomas Hanson. Minneapolis, Minn.: Bell Museum of Pathobiology, 1973. The English translation of Black’s medical degree dissertation of 1754. Brief, forty pages.
  • Brock, William H. The Chemical Tree: A History of Chemistry. New York: Norton, 2000. This reprint of a book in the Norton History of Science series is an updated survey of the history of chemistry. Black’s work is analyzed in chapters 3 and 4. Includes excellent descriptive bibliographies for all chapters, and a good index.
  • Ihde, Aaron J. The Development of Modern Chemistry. New York: Dover, 1984. This reprint of a work first published in 1964 emphasizes the evolution of chemical disciplines from the seventeenth through the twentieth centuries. Ihde analyzes Black’s work in his chapter on “pneumatic chemistry.” Includes appendices, an extensive annotated bibliography, and name and subject indexes.
  • Jungnickel, Christa, and Russell McCormmach. Cavendish: The Experimental Life. Lewisburg, Pa.: Bucknell, 1999. The award-winning first edition of this biography has been extensively revised and expanded in this updated edition, in which the influence of Black’s chemical and physical work on Cavendish is discussed. Illustrations, bibliography, and index.
  • Partington, J. R. A. History of Chemistry. Vol. 3. London: Macmillan, 1962. This comprehensive history of chemistry contains a detailed discussion of Black’s life and contributions (chapter 4). Includes many references to primary sources in the footnotes and indexes of names and subjects.
  • Ramsay, William. Life and Letters of Joseph Black, M.D. London: Constable, 1918. This work remains the only book-length biographical study of Black, and it contains letters and other primary source materials not available elsewhere.

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Stahl Postulates the Phlogiston Theory

Bernoulli Proposes the Kinetic Theory of Gases

Celsius Proposes an International Fixed Temperature Scale

Lomonosov Issues the First Catalog of Minerals

Haller Establishes Physiology as a Science

Woulfe Discovers Picric Acid

Priestley Discovers Oxygen

Cavendish Discovers the Composition of Water

Lavoisier Devises the Modern System of Chemical Nomenclature

Leblanc Develops Soda Production

Proust Establishes the Law of Definite Proportions

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Chemistry;carbon dioxide