CRAWFORD, ADAIR

(b. Ireland, 1748; d. Lymington, England, 29 July 1795)

physiology, physics, chemistry.

Little is known about Crawford’s family background or personal life. His father was a nonsubscribing Presbyterian minister in Crumlin, County Antrim. After obtaining the M.D. degree, he is said to have had a very successful practice in London. His career evidently flourished both as a result of his own achievements and through the intervention of his many influential friends. He was appointed a physician at St. Thomas’s Hospital, London; was elected to the Royal Society of London and that of Edinburgh, the Royal Irish Academy of Dublin, and the American Philosophical Society; and became professor of chemistry at the Royal Military Academy, Woolwich. Perhaps his emphasis upon experimentation and his use of phlogistic arguments owed something to the influence of his friends Joseph Priestley and Richard Kirwan. He died shortly after poor health had forced him into retirement.

From 1764 to 1776 Crawford studied arts, theology, and medicine at the University of Glasgow. In the course of his medical studies he heard William Irvine lecture on his new theory of heat, and Crawford later joined the chemical society that Irvine organized in Glasgow. Irvine had spent several years as Joseph Black’s pupil and assistant during the period in which Black was developing his theory of latent heat. Irvine’s particular task had been to measure the specific heats of various substances. Unlike Black, whose theory proceeded from the assumption that the absorption of heat is a chemical process, Irvine viewed heat as being physically contained in substances having varying capacities for it. He further argued that his theory of capacities enabled him to determine the absolute zero point of temperature and the absolute quantity of heat in a body. Irvine was appointed lecturer in chemistry at the University of Glasgow in 1770, and by 1775 he was presenting a fully developed account of his new theory in his lectures. It was this theory that captured Crawford’s attention in 1776, and it was as a champion of Irvine’s theory that he made his mark as a scientist.

In the summer of 1777 Crawford performed the first experiments designed to determine the specific heats of gases. He believed that respiration, which causes a chemical change in air, also changes the air’s capacity for heat. According to this application of Irvine’s theory, the air that supports respiration has a greater capacity for heat—that is, a higher specific heat—than the air given off by respiration. Thus, in breathing, a certain quantity of “absolute heat” is transferred to the body and, Crawford concluded, is the source of the body’s heat. In 1777 Crawford enrolled in the University of Edinburgh medical school, where he read an account of his experiments to the student medical society; and the following year he described his work to Thomas Reid and several other professors in Glasgow. He then published it as Experiments and Observations on Animal Heat, and the Inflammation of Combustible Bodies; Being an Attempt to Resolve These Phaenomena Into a General Law of Nature (London, 1779).

To establish the truth of his theory, Crawford put forward three fundamental propositions. The first states that the atmospheric air inhaled into the lungs contains more absolute heat than the air exhaled from the lungs. His experiments on the specific heats of gases were designed to verify this proposition. The second asserts that the arterial blood leaving the lungs contains more absolute heat than the venous blood pumped to the lungs. The truth of this proposition is proved, he argued, by the calorimetric experiments on blood described in his book. The third proposition states that a body’s capacity for heat is reduced by the chemical fixation of phlogiston and is increased by the separation of phlogiston.

On the basis of his third proposition Crawford constructed a general theory of combustion. He began his argument by demonstrating that metallic calxes, which are products of combustion and are, according to the phlogiston theory, dephlogistieated, have higher heat capacities than do the metals from which they are formed. Then, to explain how respiration causes a release of “absolute heat,” he appealed to the analogy between combustion and respiration and suggested that during respiration a double decomposition takes place in the lungs, atmospheric air and venous blood yielding phlogisticated air and arterial blood [(air + heat) + (blood + phlogiston) → (air + phlogiston) + (blood + heat)]. Apparently Crawford was not aware that this view of respiration obscures the distinction between Black’s chemical theory of heat and Irvine’s physical theory of capacities.

Crawford’s book attracted considerable attention. Its attempt to explain animal heat in physicochemical terms was not especially novel or shocking; but in providing the first published account of Irvine’s theory of capacities, it seriously challenged the chemical theories of heat advanced by Black and Lavoisier. The scientific “intelligencer” J. H. de Magellan provided a lengthy description of Crawford’s experiments in his Essai sur la nouvelle théorie du feu élémentaire, et de la chaleur des corps (London, 1780) and claimed: “We owe the birth of this branch of natural philosophy to the publication of this excellent work by Dr. Adair Crawford, “After visiting Paris in 1781. J. A. Deluc reported: “Dr. Crawford’s theory on the phenomena of heat… was then in great agitation.” The challenge posed by Crawford’s theory was soon taken up by Lavoisier and Laplace. In 1782 they began a series of experiments on the specific heats of gases and heats of combustion that led them to conclude, in their “Mémoire sur la chaleur,” that no reliable figure for absolute zero could be established and that Irvine’s theory therefore remained a highly dubious hypothesis.

A greatly enlarged but not fundamentally altered second edition of Crawford’s book was published in 1788. By then his critics had come to realize that the available experimental data on the specific heats of gases were too imprecise to permit a resolution of the central theoretical issue. Irvine’s theory remained influential in Great Britain, however, largely through the advocacy of John Dalton, who admitted that he was “overawed by the authority of Crawford.” But in 1812 the prize-winning work of Francois Delaroche and J. E. Bérard provided experimental values for the specific heats of gases and finally rendered the theory of capacities untenable.

BIBLIOGRAPHY

I. Original Works. In addition to the two editions of his book mentioned in the text, Crawford published two papers in Philosophical Transactions of the Royal Society: “Experiments on the Powers That Animals, When Placed in Certain Circumstances, Possess of Producing Cold,” 71 (1781), 479-491; and “Experiments and Observations on the Matter of Cancer, and on the Aerial Fluids Extricated From Animal Substances by Distillation and Putrefaction; Together With Some Remarks on Sulphureous Hepatic Air,” 80 (1790), 391 -426. The archives of the Royal Society contain an MS that Crawford read on 6 Dec. 1787, “Experiments and Observations on the Stability of Heat in Animals.” “On the Medicinal Properties of Muriated Barytes,” which contains the first description of strontium, was published in Medical Communications (of the Society for Promoting Medical Knowledge), 2 (1790), 301-359; and An Experimental Enquiry Into the Effects of Tonics, and Other Medicinal Substances, on the Cohesion of the Animal Fiber was edited by his younger brother, Alexander Crawford (London, 1816). An MS note and letter by Crawford are in G. W. Corner and William Goodwin, “Benjamin Franklin’s Bladder Stone,” in Journal of the History of Medicine,8 (1953). 359-377.

II. Secondary Literature. Everett Mendelsohn, Heat and Life, the Development of the Theory of Animal Heat (Cambridge, Mass., 1964), discusses Crawford’s place in the history of physiology and gives references to translations of his book and the writings of his critics. Crawford’s theory of combustion is analyzed in J. R. Partington and Douglas McKie, “Historical Studies on the Phlogiston Theory. III. Light and Heat in Combustion,” in Annals of Science,3 (1938), 337-371; and in J. R. Partington, A History of Chemistry. Ill (London, 1962). 156-157. Crawford’s contributions to calorimetry are examined in Douglas McKie and Niles H. de V. Heathcote, The Discovery of Specific and Latent Heats (London, 1935), 126-129, 136. For an account of the heat theories of Black and Irvine, see A. L. Donovan, Philosophical Chemistry in the Scottish Enlightenment: The Doctrines and Discoveries of William Culien and Joseph Black (Edinburgh, 1975), 222-249, 265-276. On Crawford’s influence on Lavoisier, see Robert J. Morris, “Lavoisier and the Caloric Theory,”in British Journal for the History of Science, 6 (1972), 1-38. On the study of the specific heats of gases in France, see Robert Fox, The Caloric Theory of Gases From Lavoisier to Regnauli (Oxford, 1971).

Arthur Donovan