Black, Joseph

(b. Bordeaux, France, 16 April 1728; d. Edinburgh, Scotland, 6 December 1799)

chemistry, physics, medicine.

A founder of modern quantitative chemistry and discoverer of latent and specific heats, Joseph Black, although born in France, was by blood a pure Scot. His father, John Black, was a native of Belfast; his mother, Margaret Gordon, was the daughter of an Aberdeen man who, like John Black, had settled in Bordeaux as a factor, or commission merchant, in the wine trade.

John Black and Margaret Gordon were married at Bordeaux in 1716, apparently in the Catholic faith. Joseph, fourth of their twelve children, was first educated by his mother. At the age of twelve he was sent to Belfast, where he learned the rudiments of Latin and Greek in a private school. About 1744 he crossed the North Channel to attend, as did so many Ulster Scots, the University of Glasgow. Here he followed the standard curriculum until, pressed by his father to choose a profession, he elected medicine. At this point he began the study of anatomy and attended the lectures in chemistry recently inaugurated by William Cullen. These lectures were the decisive influence on Black’s career; chemistry captivated him, and for three years he served as Cullen’s assistant. So began a close friendship that lasted until Cullen’s death.

In 1752 Black left Glasgow for the more prestigious University of Edinburgh, which boasted on its medical faculty the great anatomist Alexander Monro primus, the physiologist Robert Whytt, and Charles Alston, a botanist and chemist who lectured on materia medica. Black gained less, he said, from their lectures than from the bedside clinical instruction provided by the university’s Royal Infirmary. Alston’s lectures pleased him most, although he found him deficient in chemical knowledge, a matter of concern, for, as he wrote to Cullen, “no branch should be more cultivated in a medical college.”¹

In 1754 Black received the M.D. with his now historic dissertation De humore acido a cibis orto et magnesia alba. The next year, before the Philosophical Society of Edinburgh, he described the chemical experiments, considerably expanded, that had formed the second half of his dissertation. This classic paper—the chief basis of Black’s scientific renown and his only major publication—appeared in 1756 in the Society’s Essays and Observations under the title “Experiments Upon Magnesia Alba, Quicklime, and Some Other Alcaline Substances.” Here Black demonstrated that an aeriform fluid that he called “fixed air” (carbon dioxide gas) was a quantitative constituent of such alkaline substances as magnesia alba, lime, potash, and soda.

The same year, 1756, brought Cullen to Edinburgh as professor of chemistry, and saw Black—at the age of twenty-eight Cullen’s outstanding student—replace him in Glasgow. Here Black spent the next ten years. Although this period is sparsely documented, we know that he soon emerged as a gifted and effective teacher. His course in chemistry, launched in 1757–1758, proved so popular that many students, some with no particular relish for the subject, pressed to attend. Alongside his teaching, Black carried on an active and demanding medical practice; and since Glasgow, unlike Edinburgh, was administered by its faculty, he was constantly pressed upon by multifarious college duties. Yet it was at Glasgow that he developed his ideas about latent and specific heats—the second of his major scientific achievements—and carried out experiments, alone or with his students, to confirm his theories. These important discoveries he could never be induced to publish.

In 1766 Black received the call to Edinburgh. William Cullen relinquished the chair of chemistry to succeed Robert Whytt as professor of the Institutes of Medicine, and Black took over Cullen’s chair. At Edinburgh he was destined to remain. Although his duties were less onerous than at Glasgow-he limited his medical practice to the care of a few close friends like David Hume-his period of scientific creativity was at an end. Two short papers on insignificant subjects were his only publications. The teaching of chemistry now became his central concern; here, as at Glasgow, he became an idol to the medical students and to many others as well. Each year, from October to May, he delivered a series of more than a hundred lectures, and sometimes offered a course during the summer months.

Black’s pedagogic achievement at least equals that of his great French contemporary, G.-F. Rouelle. Although he had no student of the stature of Lavoisier, there were many of great ability. His audience was surprisingly cosmopolitan; although French students were rare, men came from Germany, Switzerland, Scandinavia, and from as far away as Russia and America, attracted by the reputation of the Scotch medical schools and of Black himself. Lorenz Crell, known as editor of early chemical journals, was one of his German students. To Edinburgh from the American colonies came such men as James McClurg, Later a successful Richmond physician, and the still more famous Benjamin Rush. Black’s British students were no less gifted. At Glasgow there were John Robison, who was to bring out in 1803 his master’s Lectures on chemistry, and William Irvine, Black’s collaborator in the work on specific heat. His Edinburgh students included Thomas Charles Hope, who succeeded him in 1797; Daniel Rutherford, the discoverer of nitrogen; and John McLean, who emigrated to America in 1795, where he became Princeton’s first professor of chemistry. Among the last to hear Black lecture were Thomas Young, the versatile physician, physicist, and linguist; the elegant and prolific Henry Brougham; and Thomas Thomson, chemist and pioneer historian of chemistry.

There are several contemporary descriptions of the appearance, personality, and lecturing skills of this great teacher. On the platform he was an immaculate figure; his voice was low but so clear that he was heard without difficulty by an audience of several hundred. His style was simple, his tone conversational, far different from Rouelle’s flamboyance. He spoke extemporaneously from the scantiest of notes; yet his lectures, of which numerous manuscript versions by his students have survived, were models of order and precision: the facts and experiments led a listener by imperceptible degrees to the theories and principles by which he explained them. Vivid accounts of his own discoveries, and demonstration experiments conducted with unvarying success were the highlights of his performance. He kept abreast of the progress of chemistry: through the years the outline of the lectures remained the same, but new material was added as chemistry, that “opening science,” as he called it, steadily advanced; and Black told his students of new discoveries it, steadily, advanced; and Black and theories, and of the men who had made them.

Black was a typical valetudinarian; never robust, he suffered all his life from chronic ill health, perhaps pulmonary in origin. With only limited reserves of energy, he nevertheless managed by careful diet and moderate exercise-hours of walking were part of his regimen-to husband his strength. In his prime, as the portrait by David Martin depicts him, he was a handsome man; and even in old age his appearance was impressive. Henry Cockburn, who saw Black in his last years, gives the following description:

He was a striking and beautiful person; tall, very thin, and cadaverously pale; his hair carefully powdered, though there was little of it except what was collected in a long thin queue; his eyes dark, clear, and large, like deep pools of pure water. He wore black speckless clothes, silk stockings, silver buckles, and either a slim green silk umbrella, or a genteel brown cane. The general frame and air were feeble and slender. The wildest boy respected Black. No lad could be irreverent towards a man so pale, so gentle, so elegant, and so illustrious. So he glided, like a sprit, through our rather mischievous sportiveness, unharmed.²

And so we see him, on one of his increasingly rare strolls, pictured by the sharp eye of the caricaturist John Kay: slim, slightly stooped, an intent and pensive figure.

Black never married, but he was no recluse. Cal. self-possessed, gentle, and a trifle diffident, he neverthless enjoyed conviviality. Until at last his health failed him, he frequented, besides the Philosophical Society and the Royal Society of Edinburgh which replaced it in 1783, those those informal clubs for which Edinburgh was famous: the Select, the Poker, and the Oyster. The Oyster, a weekly dining club, was his favorite; indeed, with his two closest friends, Adam Smith and the geologist James Hutton, he had founded it. Other members were his cousin Adam Ferguson, William Cullen, Dugald Stewart, John Playfair, and James Hall: in a word, the scientific luminaries of that remarkable Scotch Renaissance. Since the industrialists of the region were of at table—Jonh Roebuck, Lord Dundonald, for example, and visitors like Henry Cort—the Oyster might be compared with the famous Lunar Society of Birmingham, for discussion of ten turned on the role of science in technological progress.

One after another Black’s friends passed from the scene: Cullen in 1790 and William Robertson, principal of the University of Edinburgh, in 1793. Adam Smith was the first of the triumvirate to die, but increasing infirmity afflicted the two surviving members. Hutton, wasted by years and illness, fell gravely ill in the winter of 1796/97. Black, too, found his feeble strength waning. He gave his last full course of lectures in 1795–1796; but, aware of his debility, he chose Thomas Charles Hope as his assistant and eventual successor. The next year his health worsened, and Hope in effect took over. For a time Black’s health improved slightly, and he lingered on two more years. The manner of his death was so peaceful, in a way so characteristic of his methodical and undramatic life, that it has been several times recounted. Curiously, the early authorities on Black’s life are mistaken about the date of his death, variously given as November 26 (Adam Ferguson, John Robison, and Lord Brougham) and November 10 (Thomson, also quoted by his modern biographer, Sir William Ramsay). But a letter from Robison to James Watt settles the point: Black died on 6 December 1799, in his seventy-second year. ³

By scrupulous frugality, Black had quietly amassed a substantial competence, something in excess of £20,000. In his will, this sum was divided among his numerous heirs according to an ingenious, and of course mathematical, plan. Black had a certain reputation for parsimony—it is said that he weighed on a balance the guineas his students paid to attend his course—and his biographers have felt obliged to set the record straight by citing instances of his generosity: the loans he made to friends, the poor patients he treated without charge, and even the spaciousness of his house and the plenty of his table, “at which he never improperly declined any company.”⁴ He was, at the very least, as methodical in his financial affairs as he was in his science, his teaching, and all the other aspects of his life.

Black’s investigation of alkaline substances had a medical origin. The presumed efficacy of limewater in dissolving urinary calculi (“the stone”) was supported by the researches of two Edinburgh professors, Robert Whytt and Charles Alston. It interested Cullen as well, and Black came to Edinburgh as a medical student with the intention of exploring the subject for his doctoral dissertation.

But at this moment Whytt and Alston were at loggerheads: they disagreed as to the best source, whether cockleshells or limestone, for preparing the quicklime. And they differed as to what occurs when mild limestone is burned to produce quicklime. Whytt accepted the common view that lime becomes caustic by absorbing a fiery matter during calcination, and thought he had proved it by showing that quicklime newly taken from the fire was the most powerful dissolvent of the stone. Alston, in an important experiment on the solubility of quicklime, showed that this was not the case, and that the causticity must be the property of the lime itself. Both men were aware that on exposure to the air quicklime gradually becomes mild, and that a crust appears on the surface of limewater. For Whytt, this resulted from the escape of fiery matter; but Alston, noting that the crust was heavier than the lime in solution, hinted that foreign matter, perhaps the air or something contained in it, produced the crust. Yet he was more disposed to believe that the insoluble precipitate formed when the quicklime combined with impurities in the water. Black, although he had criticized Alston as a chemist, was soon to profit from his findings.

Preoccupied at first with his medical studies, Black did not come to grips with his chosen problem until late in 1753. When he did so, he found it expedient to avoid any conflict between two of his professors; instead of investigating limewater, he would examine other absorbent earths to discover, if possible, a more powerful lithotriptic agent. He chose a white powder, magnesia alba, recently in vogue as a mild purgative. Its preparation and general properties had been described by the German chemist Friedrich Hoffmann; although it resembled the calcareous earths, magnesia alba was clearly distinguishable from them.

Black prepared this substance (basic magnesium carbonate) by reacting Epsom salts (magnesium sulfate) with pearl ashes (potassium carbonate). He treated the purified product with various acids, noting that the salts produced differed from the corresponding ones formed with lime. The magnesia alba, he observed, effervesced strongly with the acids, much like chalk or limestone.

Could a product similar to quicklime be formed by calcining magnesia alba? Would its solutions have the causticity and solvent power of limewater? Black’s effort to test this possibility was the turning point of his research. When he strongly heated magnesia alba, the product proved to have unexpected properties. To be sure, like quicklime, this magnesia usta did not effervesce with acids. But since it was not sensibly caustic or readily soluble in water, it could hardly produce a substitute for limewater.

The properties of this substance now commanded Black’s entire attention, notably the marked decrease in weight that resulted when magnesia alba changes into magnesia usta. What was lost? Using the balance more systematically than any chemist had done before him, he performed a series of quantitative experiments with all the accuracy he could command. Heating three ounces of magnesia alba in a retort, he determined that the whitish liquid that distilled over accounted for only a fraction of the weight lost. Tentatively he concluded that the major part must be due to expelled air. Whence came this air? Probably, he thought, from the pearl ashes used in making the magnesia alba; for Stephen Hales, he well knew, had shown long before that fixed alkali “certainly abounds in air”⁵ If so, upon reconverting magnesiausta to the original powder, by combining it with fixed alkali, the original weight should be regained. This he proved to his satisfaction, recovering all but ten grains.

Magnesia usta, he soon found, formed with acids the same salts as magnesia alba, although it dissolved without effervescence. Only the presence or absence of air distinguished the two substance: magnesia alba loses its air on combining with acids, whereas the magnesia usta had evidently lost its air through strong heating before combining with acids.

Could the same process— the loss of combined air—also explain the transformation of lime into quicklime? Tentative experiments suggested something of the sort; but not until the work on magnesia was completed, late in 1753, did he examine this question. When he precipitated quicklime by adding common alkali, the white powder that settled out had all the properties of chalk, and it effervesced with acids. Early in 1754, Black wrote William Cullen that he had observed interesting things about the air produced when chalk was treated with acid: it had a pronounced but not disagreeable odor; it extinguished a candle placed nearby; and “a piece of burning paper, immersed in it, was put out as effectually as if it had been dipped in water.” ⁶ This was an observation clearly worth pursuing. Nevertheless, he could no longer postpone the writing of his Latin dissertation and his preparation for his doctoral examination.

The dissertation is in two parts: the first, dealing with gastric acidity, was clearly added to give medical respectability to the work; Black was never happy about it, and hoped it would pass “without much notice” ⁷ The second set forth the experiments on magnesia alba and the tentative conclusions he drew from them. Nothing of significance was said about other alkaline substances or about what he was to call “fixed air”.

The “Experiments,” on the other hand, is a longer and more elaborate work. Like his dissertation, it is divided into two parts. In Part I, he recounts the experiments on magnesia alba; little or nothing is added, but now his theory is presented without equivocation: this substance he now describes as “a compound of a peculiar earth and fixed air” ⁸

In Part II, Black describes experiments that enabled him to generalize the theory and to support his explanation of causticity. When lime is calcined, air is given off in abundance, and the caustic properties of the resulting quicklime do not derive from some fiery matter, but from the lime itself. He showed by experiment, in effect confirming what Alston had already done, that all of a given amount of quicklime, not merely a part of it, is capable of solution, if enough water is used. Thus the mysterious property of causticity is associated with a definite chemical entity having a definite solubility. As in the case of magnesia, he showed that calcareous earth combines with the same quantity of acid whether it is in the form of chalk (combined with air) or of quicklime. Again quicklime, made from a measured weight of chalk, when saturated with a fixed alkali can be converted into a fine powder nearly equal in weight to the original chalk. The quicklime was evidently saturated with air obtained from the alkali.

Black’s theory also explained the production of strong or or caustic alkalies (e.g., caustic potash) prepared by boiling quicklime with a solution of a mild alkali. What must occur is not, as chemists thought, that the acrimony of the potash is derived from the lime, but that fixed air is transferred from the mild alkali to the quicklime, thereby uncovering the inherent causticity of the alkali. Careful experiments confirmed this new extension of his doctrine.

A conclusive test of his theory of inherent causticity was Black’s demonstration that both quicklime and magnesia usta could be produced by the “wet way,” without the use of fire. He argued that if caustic alkali is caustic when not combined with “fixed air,” it should separate magnesia from combination with acid and deposit it as magnesia usta. This he easily demonstrated. He performed a similar experiment with chalk.

An important collateral investigation stemmed from Black’s experiments on the solubility of quicklime. Although he established to his satisfaction that it could be almost completely dissolved, he was puzzled not to find a larger residue of insoluble matter, for the air dissolved in water ought to combine with the quicklime to form a small amount of insoluble earth (carbonate). Perhaps the air had been driven off when the water was saturated with quicklime. The rough experiment to test this was performed after he had presented his major results to the Philosophical Society. In the receiver of an air pump, Black placed a small vessel containing four ounces of limewater; alongside it he put an identical vessel containing the same quantity of pure water. When the receiver was exhausted, the same amount of air appeared to bubble from both vessels. Clearly, the limewater contained dissolved air, but not of the kind that combined so readily with quicklime. In his “Experiments” he wrote: “Quicklime therefore does not attract air when in its most ordinary form, but is capable of being joined to one particular species only.”⁹ This he proposed to call “fixed air,” preferring to use a name already familiar “in philosophy,” rather than invent a new one. The nature and properties of this substance, he wrote, “will probably be the subject of my further inquiry.”¹⁰

Black had shown that a particular kind of air, different from common air, can be a quantitative constituent of ordinary substances and must enter, as Lavoisier put it later, into their “definition.” But he was not destined to make the investigation of such elastic fluids his “future inquiry.” This was to be mainly the work of his British disciples—Mac Bride, Cavendish, Priestly, and Rutherford—and he published nothing further on the subject. Nevertheless, from his Lectures and other bits of evidence we learn that his discoveries did not end abruptly with the publication of his “Experiments.” He knew that “fixed air” did not support combustion, that it had a density greater than common air, and that its behavior with alkaline substances resembled that of a weak acid. By experiments with birds and small animals, he soon demonstrated that this air would not support life. Using the limewater test, he showed that air expired in respiration consisted mainly of “fixed air”; and likewise that the elastic fluid given off in alcoholic fermentation, like that produced in burning charcoal, was identical with the “fixed air” yielded by mild alkalies when they effervesce with acids.

Black’s doctrines did not have the prompt success on the Continent that they enjoyed in Britain. His influence on the early stages of the chemical revolution in France was far less than scholars have imagined; indeed, at first it was negligible. Before 1773 Frence chemists were unfamiliar with his “Experiments,” which had appeared in English in an obscure publication. What they knew of his work derived largely from the arguments advanced against him by the German chemist J.F. Meyer, whose rival theory of acidum pingue was for a time widely credited. Black’s case would surely have been strengthened had he published the simple experiment, performed at Glasgow in 1757 or 1758, of directly impregnating a solution of caustic alkali with the “fixed air” expelled from chalk or limestone, and so obtaining a product both effervescent and mild.

Black’s discoveries concerning heat, the major achievement of his Glasgow period, were originally stimulated by William Cullen. In 1754 Cullen noted a striking phenomenon—the intense cold produced when highly volatile substances like ether evaporate—and he promptly wrote Black about his experiment. At about this time, Black set down in a notebook a curious observation made by Fahrenheit: water can be cooled below the freezing point without congealing; yet if shaken, it suddenly freezes and the thermometer rises abruptly to 32° on Fahrenheit’s scale. This, Black speculated, might be due to “heat unnecessary to ice.”

Fahrenheit’s observation was recorded in Boerhaave’s Elementa chemiae, a famous work that Cullen, and later Black, recommended in the English version of Peter Shaw to their students. This observation was hard to reconcile with the prevailing view that when water is brought near the freezing point, withdrawal of a small increment of heat must bring prompt solidification. But Fahrenheit’s experiment showed that solidification (or liquefaction) required the transfer of substantial quantities of heat: of heat lying concealed and not directly detectable by the thermometer; of heat, to use Black’s term, that was latent. Upon reflection, Black saw this notion to be quite consistent with commonly observed facts of nature. Snow, for example, requires a considerable time to melt after the surrounding temperature has risen well above the freezing point. A gradual absorption of heat must therefore be taking place, although the temperature of the snow remains unaltered.

Black became convinced of the reality of this latent heat through thoughtful reading and meditation on the familiar phenomena of change of state. He presented his doctrine in his Glasgow lectures, perhaps as early as 1757–1758, before he had performed any experiments of his own. Nor did his doctrine arise from any firmly held theory as to what heat might be.

Not until 1760 did Black carry out his earliest experiments on heat. The first fact to be ascertained was the reliability of the thermometer as a measuring tool. Would a thermometric fluid, having received equal increments of heat, show equal increments of expansion? Ingenious and simple experiments on mixing amounts of hot and cold water (Lectures, I, 56–58) convinced him that the scale of expansion of mercury, over that limited range, was indeed a reliable scale of “the various heats, or temperatures of heat.”

Crucial to Black’s experiments was his recognition of the distinction between quantity of heat and temperature, between what we sometimes describe as the extensive and intensive measures of heat. Although not the first to note this distinction, he was the earliest to sense its fundamental importance and to make systematic use of it. In his lectures, which always opened (after certain preliminaries) with a careful discussion of heat, he would tell his students:

Heat may be considered, either in respect of its quantity, or of its intensity. Thus two lbs. of water, equally heated, must contain double the quantity that one of them does, though the thermometer applied to them separately, or together, stands at precisely the same point, because it requires double the time to heat two lbs. as it does to heat one.¹¹

Temperature, of course, is read directly from the thermometer. But how to measure the quantity of heat? Black’s answer is implied in the above quotation: the time required to warm or cool a body to a given temperature is related to the amount of heat transferred. This elusive quantity required a dynamic measurement: the heat gained or lost should be proportional to the temperature and the time of heat flow “taken conjointly.”¹² Here, as so often in his career, the influence of Newton is quite apparent. In a famous paper of 1701, had used a dynamic method to estimate temperatures beyond the reach of his linseed oil thermometer. Black in his lectures gave a clear account of Newton’ experiments and how his law of cooling (as we now call it) was used to estimate relative temperatures above that Newton’s dynamic method was the key to Black’s.

Characteristically, Black was not satisfied to demonstrate qualitatively that there is such a thing as the latent heat of fusion: he proposed to measure it. The method occurred to him in the summer of 1761. First cooling a given mass of water to about 33°F., he would determine the time necessary to raise its temperature one degree, and compare this with the time required to melt the same amount of ice. Conversely, he would compare the time necessary to lower the temperature of a mass of water with the time necessary to freeze it completely. Assuming that both systems received heat from, or gave up heat to, the surrounding air at the same rate, as much heat should be given off in freezing a given amount of water as in melting the same amount of ice. Obliged to wait until winter, Black carried out the experiment in December 1761 in a large hall adjoining his college rooms. The following April he described his results to his Glasgow colleagues and friends.

Black soon saw that latent heat must play a part in the vaporization of water as well as in the melting of ice. The analogy was so persuasive that as early as 1761—before testing his conjecture by experiment—he presented this version of his doctrine to his students. The success of the freezing experiments soon led him to investigate the latent heat of vaporization. But the method he first employed, a precise analogue of Fahrenheit’s observation on super cooled water, was unsuited to measurement. A better method could be modeled on his freezing experiments. Tin vessels, containing measured amounts of water, would be heated on a red-hot cast iron plate. The time necessary to heat the water from 50°F. to the boiling point would be compared with the time necessary for the water to boil away. The chief obstacle was to find a source of heat sufficiently unvarying so that the absorption of heat could be safely measured by the time. A “practical distiller” informed Black that when his furnace was in good order, he could tell, to a pint, the quantity of liquor that he would get in an hour. When Black confirmed this by boiling off small quantities of water on his own laboratory furnace, he was ready for the experiments. ¹³ These he performed late in 1762. From the average of three experiments he calculated that the heat absorbed in vaporization was equal to that the which would have raised the same amount of water to 810, were this actually possible. This gives a figure of 450 calories per gram for the latent heat of vaporization of water, compared to a modern figure of 539.1 calories per gram. More accurate figures were obtained in later experiments, but several years elapsed before Black took up the subject again.

The second, and closely related, discovery made by Black concerning heat was that different substances have different heat capacities. It is commonly assumed that Black discovered specific heats before his work on latent heat. This is not the case. To be sure, the clue, once again, was found in Boerhave’ text-book; Fahrenheit had made certain experiments at his request and had obtained the surprising result that when he mixed equal quantities of mercury exerted far less effect in heating or cooling the mixture than did the water. At first Black was puzzled; but he soon realized that mercury, despite its greater density, must have a smaller store of heat than an equal amount of water at the same temperature. If so, the capacities of bodies to store up heat did not vary with their bulk or density, but in a different fashion “for which no general principle or reason can yet be assigned.”¹⁴ Now Black could explain a peculiar effect reported twenty years earlier by George Martine, an authority on thermometers. Martine had placed equal volumes of water and mercury in identical vessels before a fire, and observed that the mercury increased in temperature almost twice as fast as the water. Black saw that since less heat was required to bring mercury up to a given temperature, a thermometer placed in it should rise more rapidly. Not until 1760 did Black perceive the significance of this effect, but he did not pursue the significance of this effect, but he did not pursue the subject; he was principally absorbed with the more striking phenomena of changes of state. In 1764—a year that James Watt made memorable in the history of invention—Black returned to the study of heat. His experimental inquiry into specific heats, and his attempts to obtain a more accurate value for the latent heat of vaporization, were stimulated by the activities of Watt.

The year that Black began his Glasgow lectures, James Watt, a young man of nineteen, skilled in making mathematical instruments, was taken under the wing of the university as what we might today call a technician. He was soon called upon by Black to make things he needed for his experiments. Watt, in turn, after repairing the now-famous model of a Newcomen engine and undertaking experiments to improve its performance, turned to Black to explain an effect he could not comprehend. He was astonished at the large amount of cold water required to condense the steam in the engine cylinder, until Black explained his ideas about latent heat.

Watt was many months, and many experiments, away from hitting upon the historic invention of the separate condenser, and Black may be pardoned for believing that this disclosure inspired Watt’s radical improvement of the steam engine, a claim advanced even more strongly by John Robison, who spoke of Watt as Dr. Black’s most illustrious pupil. This, in a strict sense, Watt never was; and, despite his lifelong attachment to Black, he later insisted that the invention of the separate condenser had not been suggested by his knowledge of the doctrine of latent heat. But he readily credited Black with having clarified the problems he encountered and with teaching him “to reason and experiment in natural philosophy.”¹⁵

On the other hand, Watt’s ingenuity and questioning mind, and the practical problems he raised, revived Black’s interest in heat. The problems he now investigated with John Robison and William Irvine were closely related to those Watt needed to elucidate. Irvine was set to work determining a more accurate value of the latent heat of steam. Using a common laboratory still as a water calorimeter, Irvine obtained improved values, although these were not high enough to be really accurate. Black, it should be remarked, never made or used the mythical ice calorimeter associated with his name, although it occurred to him in the spring or summer of 1764 that his knowledge of the latent heat of fusion of ice could be used to measure the latent heat of fusion of ice could be used to measure the latent heat of steam. Plans to put this to the test were set aside when Watt, late in 1764, began to obtain values that Black deemed sufficiently precise. Years later, Black gave the French scientists full credit for the independent invention and first use of an ice calorimeter. ¹⁶

The measurements made at this time by Black, Irvine, and Watt on the specific heats of various substances are the earliest of which we have any trace. Watt seems to have been the first to stress the importance of investigating the subject systematically. He carried out experiments of his own, and Black put Irvine to work on the problem. Using the method of mixtures, Black and Irvine determined the heats communicated to water by a number of different solids. These joint experiments continued until Black left for Edinburgh. After Black’s departure, Irvine continued these investigations, but his results were not published in his lifetime.

Joseph Black’s view of chemistry, his chemical doctrines, can be derived from his single major paper and from the various versions of his lectures. Chemistry, to him, was a subject with wide practical application to medicine and to the progress of industry. But he insisted, as Cullen had done, that it is a science, albeit an imperfect one, not merely, natural or artificial, with a view to the improvements of arts and natural knowledge.”¹⁷

On the question of the “elements” or “principles” of bodies, Black showed a typical caution. He no longer credited the venerable doctrine of the four elements; little could be known about them, for there was knowledge of the underlying constitution and forces of nature. It was more sensible to group into several classes, as Cullen did, those substances sharing certain distinguishable properties: the salts, earths, inflammable substances, metals, and water. These were not necessarily elementary; of earths there were several sorts that could not be decomposed further; water, Black believed, can on distillation be converted into earth; and there was reason to suspect that salts were not compounds of earth and water, but of an earth and some other unknown substance.

Black invariably devoted the early lectures of his course to the subject of heat, telling his students that Boerhaave, Robert Boyle, and Sir Isaac Newton followed Lord Bacon in believing that heat is caused by motion, and that the French thought heat to be the vibration of an imponderable, elastic fluid. The fluid theory was the one to which he quite definitely leaned, for it seemed to agree best with the phenomena; he could not, for example, readily conceive a motion of particles in dense, solid bodies. But such questions are involved in obscurity. And he told his students; “The way to acquire to acquire a just idea of heat is to the facts.” ¹⁸

In discussing problems of combustion, fermentation, and the calcination of metals, Black— until the close of his career—presented a gingerly avoided the term. Air, of course, was required for combustion; but like his contemporaries he invoked the property of elasticity to explain its role. Combustion was caused by the presence of an inflammable principle, for which different substances had a different “elective attraction.” Inflammable and combustible substances, including the calcinable metals, were pervaded with this mysterious substance, the nature of which “we are still at a loss to explain.” Although little could be said on the subject, heat and light appeared to be the principles of inflammability. There was, however, a fact that was hard to explain and was a strong objection to this theory. When it was possible to collect the product of combustion, or weight a calcined metal, this product was heavier, despite the loss of the inflammable principle. Possibly this was a kind of matter that defied the general law of gravitation, yet speculations of this sort were not Black’ cup of tea. These doubts almost certainly prepared him to accept, in the main, Lavoisier’s discoveries.

As late as 1785 Black was reluctant to adopt the new “French chemistry,” a term he heartily disliked. The geologist Sir James Hall was the earliest of Black’s circle to sense the winds of change. A visit to Paris in 1786 convinced him, and on his return to Scotland, in the course of long discussions, he brought Thomas Charles Hope around to his opinions. Early in 1788 Hall read around to his opinions. Early in 1788 Hall read before the Royal Society of Edinburgh a paper entitled “A View of M. Lavoisier’s New Theory of Chemistry.” Black may well have been present— we cannot be sure—but his intimate friend James Hutton was, and defended the phlogistic hypothesis with a paper of his own. Never-theles, an Italian visitor to England, an admirer of Mme. Lavositor, wrote her from London in 1788 that and Watt (“in my opinion the two best heads in Great Britain”) were on the verge of being convinced by Lavoisier’s antiphlogistic theory. Soon thereafter, Black began to mention the new doctrine in his lectures; he wrote to Lavoisier, in a famous letter of October 1790, that he had began to recommend the new system to his students as simpler, and more in accord with the facts, than the old. Robison’s edition of Black’s lectures, based on what Black was telling his students between 1792 and about 1796, amply confirms his statement. Yet it is clear that Black strongly disapproved of the new nomenclature, while recognizing that advances in chemists completely he felt that the new terms were “contrived to suit the genius of the French language” and he perceived in the new scheme a clever stratagem of the French chemists to give their doctrines “universal currency and authority.” ¹⁹

The most interesting and pervasive of Black’s doctrines is the theory theory of chemical affinity. Here debt to Cullen, and beyond Cullen to to Newton’s Opticks, is clearly evident. Chemical reactions result from the differential or “elective” attraction of chemical individuals for one another. Simple elective attractions are those produced by heat; “double elective attractions,” reactions of double decomposition, are chiefly those that take place in solution. Black saw no reason for avoiding the term “attraction,” as did the French chemists who spoke instead of “affinities” or “rapports.” As Newton had insisted, “attraction” should be taken as a descriptive term, not a causal explanation.

Black’s earliest use of this concept, and of Geoffroy’s well-known table of affinities, appears in his “Experiments.’s He employs it to show the differential behavior of alkaline substances toward acids and “fixed air.” For Black, as for Cullen, this became a centrally important pedagogical device; invariably he devoted several lectures to elective attractions, describing the table, and referring to it elsewhere when speaking of particular reactions. In the lectures of the early years Black set forth these reactions with the diagrams Cullen had invented, adding numbers to indicate the relative force of attraction between substances:

Later, he used a diagram consisting of segmented circles, but without numbers to indicate the relative attractions. ²⁰ The following example illustrates what takes place when a compound of volatile alkali with any acid (e.g., ammonium chloride) reacts with a mild fixed alkali (e.g., sodium carbonate); here the “fixed air” or “mephitic air” represented by MA combines with the volatile alkali, 8; and the fixed alkali, 8, joins itself to the acid, >:

Did Black wish to represent molecules in which the atomic partners are interchanged? Perhaps this occurred to him, but he probably conceived these diagrams primarily as what we call visual aids. Unlike his master, William Cullen, Black did not explicitly link his discussion of elective attractions with the corpuscular or atomic doctrine, about which he had little to say in his lectures.

Robison records that in an early conversation Black “gently and gracefully” checked his disposition to form theories and warned him to reject “even without examination, every hypothetical explanation, as a mere waste of time and ingenuity.”²¹ Like Newton, whom he so greatly esteemed— at least Newton as he understood him—Black chose not to “deal in conjectures”.

In mid-career he told his students, well before the fulfillment of what we call the chemical revolution:

Upon the whole, Chymistry is as yet but an opening science, closely connected with the useful and ornamental Arts, and worthy the attention of a liberal mind. And it must always become more and more so: for though it is only of late, that it has been looked upon in that light, the great progress already made in Chymical knowledge, gives us a pleasant prospect of rich additions to it. The Science is now studied on solid and rational grounds. While our knowledge is imperfect, it is apt to run into errour: but Experiment is the thread that will lead us out of the labyrinth. ²²

NOTES

1. Thomson, Cullen, I, 573.

2. Henry Cock Burn, Memorials of his Times (Edinburgh, 1856), pp. 48–49.

3. Muirhead, Origin and Progress, II, 261–263.

4. Ferguson, “Minutes,” p. 116.

5.Dissertation, p. 272, amd “Experiments,” p. 17. Compare Lectures, II, 63–64.

6. Thomson, op, cit., I, 50.

7. Letter to Cullen, 18 June 1754, ibid., pp. 50–51.

8. “Experiments,” p. 25.

9.Ibid., pp. 30–31.

10.Ibid., p. 31.

11. Law, “Notes of Black’s Lectures,” 1, 5.

12.Ibid., p. 18.

13.Lectures, 1, 157,

14.Ibid., p. 79.

15. Muirhead, op. cit., 264.

16.Lectures, I, 175.

17. Cochrane, “Notes from Black’s Lectures, 1767/8,” p. 3. Black saw no reason to change his definition: see Lectures, I, 12–13.

18. Law, op. cit., I, 5. Compare Lectures, I, 35.

19.Lectures, I 489–493.

20. Henry Guerlac, “Commentary on the Papers of Cyril Stanley Smith and Marie Boas,” in Marshall Clagett, ed., Critical Problems in the History of Science (Madison, Wis., 1959), pp. 515–519. For a fuller treatment, see M. P. Cropland, “The Use of Diagrams as Chemical “Equations” in the Lecture Notes of William Cullen and Joseph Black.”. Crosland argues that Black wished to illustrate the course of chemical reactions without implying mechanical explanations and that his symbols were generalized expressions for reactions of a similar type.

21.Lectures, I, vii.

22. Law, op, cit., III, 88.

BIBLIOGRAPHY

1. Original Works. Black’s published writings are the following:

Dissertatio media inaugurals… (Edinburgh, 1754). Reprinted in Thesaurus medicus Edinburgensis novus, II (Edinburgh-London, 1785). English translation by A. Crum Brown in Journal of Chemical Education, 12 (1935), 225–228, 268–273, with facsimile of title page and dedication.

“Experiments Upon Magnesia Alba, Quicklime, and Some Other Alkaline Substances,” in Essays and Observations, Physical and Literary. Read Before a Society in Edinburgh, 2 (1756), 157–225. Republished, together with Cullen’s “Essay on the Cold Produced by Evaporating Fluids” (Edinburgh, 1777; repr. 1782). Black’s famous paper is most readily available as Alembic Club Reprints no. 1 (Edinburgh, 1898). The first French translation was “Expériences sur la magnésia blanche, la chaux vive, & sur d’autres substances alkalines, par M. Joseph Black, Docteur en Médicine,” in Observations sur la physique, 1 (1773), 210–220, 261–275. A short summary of Black’s work on magnesia had been published in the Journal de médecine, Chirurgie, pharmacie, 8 (1758), 254–261.

“On the Supposed Effect of Boiling Upon Water in Disposing It to Freeze More Readily,”, in Philosophical Transactions of the Royal Society of London, 65 (1775), 124–129.

“Lettre de M. Joseph Black à M. Lavoisier,” in Annales de chime, 8 (1791), 255–229. The English original of Black’s letter was printed by Douglas McKie in Notes and Records of the Royal Society of London, 7 (1950), 9–11.

“An Analysis of the Water of Some Hot Springs in Iceland,” in Transactions of the Royal society of Edinburgh, 3 (1794), 95–126.

Lectures on the Elements of Chemistry, John Robison, ed., 2 vols. (Edinburgh, 1803; American ed., 3 vols., Philadelphia, 1806–1807). Robison omitted Black’s introductory lecture and much of the next two or three lectures. In a letter of 16 September 1802 to James Black, Joseph’s brother, he tells of his difficulties in putting together, from Dr. Black’s sparse notes, a coherent text. He even speaks of having to “manufacture” one lecture; obviously, although Robison’s edition probably represents Black’s opinions, the language may sometimes be Robison’s. The text should be compared with the MS versions. See McKie, Annals of Science, 16 (1960), 131–134, 161–170.

“Case of Adam Ferguson, Drawn up by Joseph Black, M.D., in May, 1797,” in Medico-Chirurgical Transactions, 8 (1816). Cited and summarized by Crowther.

“A Letter From Dr. Black to James Smithson, Esq. Describing a Very Sensible Balance,” in Annals of Philosophy, n.s. 10 (1825), 52–54. Black’s letter is dated 18 September 1790.

The earliest pictures of Black are two ink sketches made by Thomas Cochrane in his notes while attending Black’s lectures in 1767–1768 in what appears to be an anatomical theater. Reproduced by McKie in Annals of Science, 1 (1936), 110, and in his edition of Cochrane’s “Notes 1767/8.”

Not much later (ca. 1770) is a fine oil by David Martin, the teacher of Sir Henry Raeburn (Collection of the University of Edinburgh). Published by Guerlac in Isis, 48 (1957) and by McKie as frontispiece to his edition of the Cochrane “Notes 1767/8.”

The most familiar portrait of Black is by Raeburn (Collection of the University of Edinburgh), showing Black at about the age of sixty; of ten reproduced, sometimes (as in the frontispiece of Robison’s edition of Black’s Lectures) from an inferior engraving.

Roughly contemporaneous with the Raeburn portrait are the sketches of John Kay: one shows Black walking in the country; another places en face a birdlike Hutton and a pensive Black. The most interesting is a close view of Black lecturing, spectacles in hand, and before him a spate of scattered notes, a syphon, a burning candle, and a small bird in a cage, all to demonstrate the properties of “fixed air.” See A Series of Portraits and Caricature Etchings by the Late John Kay, 2 vols. (Edinburgh, 1837), I, pt. 1, 52–57. Reproductions by Ramsay in his biography of Black and, more attractively, by John Read in Humour and Humanism in Chemistry, plates 41 and 44–45.

No published census of manuscript versions of Black’s lectures exists, but a few may be mentioned, together with their present locations. The earliest is Thomas Cochrane’s (Andersonian Library, University of Strathclyde, Glasgow); dating from Black’s early teaching at Edinburgh, it is otherwise notable only for the caricatures of Black. Very sketchy, it has recently been published as Notes from Doctor Black’s Lectures on Chemistry 1767/8, ed. with intro., by Douglas McKie (Cheshire, 1966).

More complete are the closely written set of 120 lectures recorded by James Johnson, 1770 (University of Edinburgh Library), and three volumes bearing the name of Joseph Freyer Rastrick and covering Black’s lectures of 1769–1770 (History of Science Collections, Cornell University Library). A fine set is the Beaufoy MS, 1771/72 (University of Saint Andrews). Quite different from others is Alexander Laws’s “Notes of Doctor Black’s Lectures on Chemistry” (University of Edinburgh Library,) with fifty-seven lectures from 13 June to 22 December 1775, and elaborate notes and appendices. For Black’s later period there are the notes of George Cayley, 6 vols., 118 lectures, 1785f-1786 (York Medical Society) and a similar set, without date or name of original owner, now at University College, London. McKie, in Annals of Science (1959), p, 73, believes this set to be contemporary with the Cayley notes.

II. Secondary Literature. A brief, uninspired account of a visit to Black in 1784 (largely devoted to a description of Black’s portable furnace) is given by the geologist Barthélemy Faujas de Saint-Fond, in his Voyage en Angleterre et en Ecosse, II (Paris, 1797), 267–272. The earliest biographical sketch is the short, anonymous account, probably by Alexander Tilloch, in Philosophical Magazine, 10 (1801), 157–158. But the most important source is Adam Ferguson, “Minutes of the Life and Character of Joseph Black, M.D.,” in Transactions of the Royal Society of Edinburgh, 5 (1805), 101–117. Ferguson was Black’s cousin and close friend. John Robison, “Editor’s Preface,” in Lectures, I, v–lxvi, draws heavily on Ferguson, yet adds much useful information. Thomas Thomson, History of Chemistry, I (London, 1830), ch. 9, relies on Ferguson and Robison, but adds personal impressions. Thomson also contributed short accounts of Black to the Annals of Philosophy, 5 (1815), 321–327, and the Edinburgh Encyclopedia. Lord Brougham, like Thomson one of Black’s last students, devotes an intersting chapter to Black in his Lives of Philosophers of the Time of George III (London-Glasgow, 1855), pp. 1–24. George Wilson’s brief note, in Proceedings of the Royal Society of Edinburgh, 2 (1849), 238, corrects the date of Black’s death as given by Ferguson and Robison, citing newspaper accounts and Muirhead.

John Playfair’s “Biographical Account of the Late Dr. James Hutton,” in Transactions of the Royal Society of Edinburgh, 5 , pp. 39–99 of the “History of the Society,” has references to Black. James Patrick Muirhead, Origin and Progress of the Mechanical Inventions of James Watt, 3 vols. (London, 1854), published numerous letters from Watt to Black, and one from Black to Watt. Also valuable is John Thomson’s Account of the Life, Lectures and Writings of William Cullen, M.D., 2 vols. (Edinburgh-London, 1859), with several early letters of Black to Cullen.

For Glasgow University in Black’s time, see Henry G. Graham, Social Life of Scotland in the Eighteenth Century, II (London, 1899), chs. 12–13; W. Innes Addison, Roll of Graduates of the University of Glasgow (Glasgow, 1898) and Matriculation Album of the University of Glasgow (Glasgow, 1913). Worth consulting is W. R. Scott, Adam Smith as Students and Professor (Glasgow, 1937). Letters of Thomas Reid in The Works of Thomas Reid, D.D., Sir William Hamilton, ed., 7th ed., I (Edinburgh, 1872), 39–50, describe Black’s Glasgow lectures. For the chair of chemistry at Glasgow, see Andrew Kent, ed., An Eighteenth Century Lectureship in Chemistry (Glasgow, 1950). For Edinburgh, consult Alexander Bower, History of the University of Edinburgh, 2 vols. (Edinburgh, 1817); and Sir Alexander Grant, Story of the University of Edinburgh, 2 vols. (London, 1884).

Agnes Clarke’s article on Black on the Dictionary ofNational Biography is disappointing and sometimes inaccurate, but gives the correct date for Black’s death. The most scientifically eminent of Black’s modern biographers is Sir William Ramsay. He first discussed Black’s work in his Gases of the Atmosphere (London, 1896), pp. 527–531, and again in his Joseph Black, M.D., A Discourse (Glasgow, 1904). His Life and Letters of Joseph Black, M.D. (London, 1918) is the only full-length biography; published posthumously, it is valuable chiefly for the use made of letters and papers of Black, including an autobiographical sketch, which have been otherwise inaccessible to scholars. Ramsay’s book is unsatisfactory; when a scholarly biography is written, and one is badly needed, use will surely be made of Henry Riddell’s “The Great Chemist, Joseph Black, His Belfast Friends and Family Connections,’ in Proceedings of the Belfast Natural History and Philosophical Society, 3 (1919/20), 49–88.

Black is, of course, discussed in the familiar histories or studies of early chemists. Most can be ignored; an exception is Max Speter’s “Balck,” in G. Bugge, Das Buch der grossen Chemiker, 2 vols. (Weinheim, 1929), I, 240–252 J. R. Partington, History of Chemistry, III (London-New York, 1962), 131–143, appraises Balck’s proficiency as a chemist and gives detailed citations of the literature. John Read has a readable, if not wholly relible, account of Balck in his Humour and Humanism in Chemistry (London 1947), ch. 8, and a brisk chapter in Kent’s Eighteenth Century Lectureship, pp. 78–98. A longer and more informative account of Black, with new insights and some inaccuracies, is J.C. Crowther, Scientists of the Industrial Revolution (London, 1962), pp. 9–92. Archibald and Nan L. Clow, The Chemical Revolution (London, 1952), has a misleading title: it deals with the applications of chemistry to industry in the eighteenth and early nineteenth centuries, and is valuable for many passing references to Black’s involvement in such matters.

Douglas McKie’s paper on the Cochrane “Notes,” in Annals of Science, 1 (1936), 101–110, has been superseded by his edition of that MS. But see his “Some MS Copies of Black’s Chemical Lectures,” ibid., 15 (1959), 65–73; 16 (1960), 1–9; 18 (1962), 87–97; 21 (1965), 209–255; 23 (1967), 1–33. E.W. J. Neave, “Joseph Black’s Lectures on the Elements of Chemistry,” in Isis, 25 (1936), 372–390, merely outlines the contents of Robision’s of Black’s Lectures.

Black’s influence on the progress of scientific medicine and biology is treated by Herinrich Buess, “Joseph Balck und die Anfänge chmischer Experimentalforschung in Biologie und Medizin,” in Gesnerus, 13 (1956), 165–189. Henry Guerlac, “Joseph Balck and Fixed Air,” in Isis, 48 (1957), 124–151, 433–456, attempts to clarify the chronology of Black’s early life and to reconstruct the steps in his chemical investigations. Guerlac’s Lavoisier, The Crucial Year (Ithaca, N.Y., 1962), pp. 8–35, 68–71, sees Stephen Hales, rather than Joseph Black, as the chief British influence on Lavoisier before 1773. M. P. Crosland has studied Balck’s teaching symbols in “The Use of Diagrams as Chemical ‘Equations’ in the Lecture Notes of William Cullen and Joseph Black,’s in Annals of Science, 15 (1959), 75–90. Twenty-six recently discovered letters by or concerning Black, inculding twenty-one written to his brother Alexander, have been published by Douglas McKie and David Kennedy, “Some Letters of Joseph Black and Others,” in Annals of Science, 16 (1960), 129–170. Inculded is the important letter by John Robison on the problems encountered in publishing Black’s Lectures.

For Black’s work on heat, consult Ernst Mach, Die Principien der Wärmelehre (Leipzig, 1896), pp. 153–181; Douglas McKie andd Niels H. de V. Heathcote, The Discovery of Specific and Latent Heats (London, 1935), pp. 1–53; and Martin K. Barnett, “The Development of the Concept of Heat From the Fire Principle of Heraclitus Through the Caloric Theory of Joseph Balck,” in Scientific Monthly, 42 (1946), 165–172, 247–257.

Henry Guerlac

Joseph Black

1728-1799

Scottish Chemist, Physicist and Physician

Joseph Black is best known for his work with gases, alkaline substances, and heat, including the development of the concepts of latent heat and specific heat. His groundbreaking work in the quantitative study of chemical reactions places him among the founders of modern chemistry.

Joseph Black was born in France. His father, who was of Scottish descent, was a wine merchant. He received his early education in Belfast, Ireland, and completed advanced studies in chemistry and medicine at the universities of Glasgow and Edinburgh in Scotland. He was appointed professor of chemistry and anatomy at the University of Glasgow in 1756 and subsequently was given the chair of medicine. He became professor of chemistry at Edinburgh University in 1766 and remained in that position until his death. He was a dedicated and thorough researcher and a very popular lecturer, attracting nonscientists as well as scientists. He also practiced medicine during his early career.

Carbon dioxide, known as "fixed air," had been discovered previously by Stephen Hales (1677-1761), but had not been studied until it was rediscovered by Black. He performed extensive quantitative studies on this gas and on the alkaline materials, known as carbonates, that give off carbon dioxide when heated. He showed that carbon dioxide acts as an acid when dissolved in water and discovered that mild alkaline carbonates become more alkaline when they lose carbon dioxide, while strong alkaline carbonates become less alkaline when they absorb carbon dioxide. He proved that this gas is produced in fermentation, respiration, and the burning of charcoal. His clear demonstration that "fixed air" differs chemically from ordinary air resulted in a clarification of the concept of gases as a state of matter and led to the subsequent discovery of a variety of other gases.

Black's development of the concepts of latent heat and specific heat were the first important discoveries in the study of heat in modern times. Observing that when ice melts or when water evaporates, heat is taken up but the temperature is not changed, he concluded that the absorbed heat becomes "latent": it is contained in the substance but is not active (i.e. does not change the temperature), yet it is available to be given off when water freezes or condenses. The amount of heat needed to melt one gram of a solid substance is its latent heat of fusion. Similarly, the heat needed to evaporate one gram of a liquid substance is its latent heat of evaporation. He also noted that when the temperature of the identical quantities of different substances is raised by the same number of degrees, different amounts of heat are required. He defined the amount of heat required to raise one gram of a substance one degree as the specific heat of that substance. To facilitate his experiments, he developed the methods of calorimetry, the quantitative measurement of the heat given off or absorbed in chemical and physical processes. His friend James Watt (1736-1819) was influenced by these ideas on heat in the development of the steam engine.

Black's careful experimental studies played a major role in the development of chemistry as a modern quantitative science, especially in the development of physical chemistry. In addition to his careful experiments, he made significant contributions to the basic understanding of important concepts in chemistry and physics. Perhaps his most notable contribution was the clarification of the concept of chemical reaction. Black applied to chemistry the Newtonian physics idea that if one agent acts upon another, the second agent will exhibit a reaction to this action. Using this terminology, he explained the chemical change that occurs when substances are mixed to be the result of the "reaction" of these substances as they act upon each other.

J. WILLIAM MONCRIEF

Joseph Black

The British chemist Joseph Black (1728-1799) is famous for his discovery of "fixed air" (carbon dioxide). He also discovered latent heat and was the first to recognize clearly the difference between intensity and quantity of heat.

Joseph Black was born on April 16, 1728, in Bordeaux, France, the son of a Scottish merchant settled in that city. Educated first at the University of Glasgow, he proceeded to the University of Edinburgh to complete his medical studies and presented his thesis there in 1754. This thesis, submitted, as was then customary, in Latin, was published in English in an expanded form in 1756 under the title Experiments upon Magnesia Alba, Quicklime, and Some Other Alcaline Substances.

The work described in this thesis sounded the death knell of the phlogiston theory and led in due course to the development of the modern system of chemistry through the work of Lavoisier and others. In his thesis Black showed by careful quantitative experiments that magnesia alba, a mild alkali, lost weight on heating; that this loss in weight was due to the release of an air, different from ordinary atmospheric air, which he named "fixed air" (now known as carbon dioxide); and that the ignited magnesia no longer effervesced with acids. Mild alkalies were thus shown to differ from caustic alkalies by containing "fixed air" in combination, and the same "fixed air" was later found by him to be produced in respiration, in fermentation, and in the combustion of charcoal. To appreciate the full significance of these results, it should be remembered that prior to Black's work it was believed that limestone (a mild alkali) on heating absorbed fiery particles (phlogiston) and was thereby converted to quicklime (a caustic alkali). Black's application of the chemical balance to the study of such chemical reactions demonstrated the falsity of this view and in the broader sense was perhaps his greatest contribution to science.

When Black moved to Glasgow in 1756 as professor of anatomy and chemistry, he turned his attention to the study of heat, applying to it the same quantitative approach he had used in his chemical work. He showed that different substances have different capacities for heat. Further studies led him to the discovery of latent heat and to the first reasonably accurate measurements of the latent heat of vaporization and freezing of water. James Watt later applied these discoveries in his development of the steam engine. Black returned to the University of Edinburgh in 1766 as professor of chemistry and medicine, a position which he occupied until his death on Dec. 6, 1799.

Further Reading

Black's work is recorded in most histories of chemistry, but an excellent account of his life and work in the setting of his times is in Andrew Kent, ed., An Eighteenth Century Lectureship in Chemistry (1950). Background works which discuss Black include Thomas W. Chalmers, Historic Researches: Chapters on the History of Physical and Chemical Discovery (1952), and Stephen Toulmin and June Goodfield, The Architecture of Matter (1962). □

Black, Joseph

SCOTTISH CHEMIST AND PHYSICIST
1728–1799

Joseph Black was trained as a medical doctor. One of his early scientific undertakings was investigating means of treating "the stone" (kidney stones and gallstones). The investigation prompted him to make a study of how to dissolve stones found in nature. Black found that certain stones, such as limestone, dissolved in mild acids, giving off large volumes of a gas. He called this gas "fixed air," as it had been "fixed" in a small volume of solid stone. Following the practice of the pneumatic chemists (chemists who were studying the properties of gases or "airs"), he trapped and characterized this new gas. "Fixed air" was found to be mildly acidic. It would later be called carbon dioxide, and stones that generated this gas would be defined as carbonates. Black also discovered that the chemical nature of the gas that had been produced in these experiments was determined by the stone it came from, not by the acid used.

Black was the first to distinguish between the temperature of an object and the heat contained in that object. He characterized "specific heat" as the amount of heat required to increase the temperature of a sample by a given amount. He recognized that it is dependent on the identity of and the amount of the material in the sample. If the sample being heated is at its melting or boiling temperature prior to the application of heat, it will absorb heat as it is going through a phase change (from solid to liquid or liquid to gas), but the temperature of the sample does not increase. The amount of heat absorbed during such a transition is also dependent on the amount of material in the sample and is characteristic of the type of material in the sample. Black termed this heat "latent heat" because it is "latent" in the sample and does not increase the temperature of the sample.

Although trained as a medical doctor, Joseph Black spent most of his professional career as an instructor in chemistry at the University of Edinburgh. His lecture notes were edited by one of his students and published as a textbook in chemistry in 1803, four years after his death.

David A. Bassett

Bibliography

Partington, J. R. (1962; reprint 1996). A History of Chemistry, Vol. 3. New York: Martino Publishing.

Black, Joseph (1728–99). Chemist who showed that gases enter into chemical reactions. Black studied medicine at Glasgow University with William Cullen, and then migrated to Edinburgh where in 1754 he submitted his MD dissertation on magnesia alba, a remedy for stomach aches. This he extended into a paper in 1756. He followed a cycle of reactions, in which ‘fixed air’ (carbon dioxide) is driven off from the stone on heating, leaving a powder akin to quicklime. With water it is slaked; and then slowly absorbs or fixes air or gas again to turn back into the starting substance. In 1756 he succeeded Cullen as professor of chemistry (within the medical school) at Glasgow, and in 1766 in Edinburgh. He also noted how much heat was needed to turn ice into cold water, or boiling water into steam: the phenomenon of latent heat. He was an early convert to Lavoisier's new chemistry.

David Knight