Black, Joseph (DNB00)
BLACK, JOSEPH, M.D. (1728–1799), an eminent chemist, was born in 1728 at Bordeaux, where his father, John Black, carried on the business of a wine-merchant. John Black was a native of Belfast, but of Scottish extraction, and married a daughter of Robert Gordon, of the Gordons of Hillhead in Aberdeenshire, like himself engaged in the Bordeaux wine trade, by whom he had eight sons and five daughters. The worth of his sterling character and well-informed mind obtained for him the friendship of Montesquieu. At the age of twelve Joseph Black was placed at a grammar school in Belfast, and in 1746 proceeded thence to the university of Glasgow. There he chose medicine as his profession, and became enamoured of chemistry through the teachings of William Cullen, the first in Great Britain to raise the science to its true dignity. Cullen noted Black's aptitude, promoted him from the class-room to the laboratory, and imparted to him, as his assistant, his own singular dexterity in experiment.
When Black went to Edinburgh to complete his medical education in 1750 or 1751, he found an active controversy in progress as to the mode of action ofthe lithontriptic medicines then recently introduced into the pharmacopœia. He took up the subject, and finding himself, in 1752, on the brink of an important discovery, he postponed tnkmyr his degree until its proofs were assured. There is, perhaps, no other instance of a graduation thesis so weighted with significant novelty as Black's ‘De humore acido à cibis orto, et Magnesia alba,' presented to the faculty 11 June 1754. Developed and perfected, it was read before the Medical Society of Edinburgh 5 June 1755, published in the second volume of ‘Essays and Observations’ (1756), with the title ‘Experiments upon Magnesia alba, Quicklime, and some other Alkaline Substances,' and subsequently twice reprinted (1777 and 1782).
As a model for philosophical investigation this essay was, by Brougham and Robison, placed second only to the ‘Optics‘ of Newton. Its importance in chemical history is two-fold. By setting an example of the successful use of the balance, it laid the foundation of quantitative analysis; and by the distinction of qualities conveyed in it between ‘fixed’ and common air, it opened the door to pneumatic chemistry. Up to that time the causticity of alkalis after exposure to strong heat had been universally attributed to an acrid principle derived from fire. Black showed that they lost instead of gained in weight by calcination; and that what they lost was a kind of ‘air' previously ‘fixed’ in them, and neutralising, by its acid qualities, their native causticity. The effervescence of ‘mild’ and non-effervescence of ‘caustic’ alkalis when dissolved in acids were alleged in countenance of the new theory, which, nevertheless, encountered a vigorous, though futile, opposition in Germany. It was pointed out in the same remarkable treatise that magnesia, until then generally held to he a variety of lime, formed, with the same acids, wholly different salts, and was consequently to he regarded as a distinct substance.
Black was fully aware of the vastness of the field of research thrown wide by the discovery (or rather individualisation) of fixed air, named by Lavoisier in 1784 ‘carbonic acid’ (Mém. de l'Acad. 1781, p. 455). In 1757 he ascertained its effects upon animals, and its production by respiration, fermentation, and the burning of charcoal (Lectures, ii. 87–8). He also inferred its invariable presence, in small quantities, in the atmosphere. Here, however, he stopped, leaving the path which he had struck out to be pursued by Cavendish, Priestley, and Lavoisier.
On the removal of Cullen to Edinburgh, Black was appointed in 1756 to replace him in the chair of anatomy and chemistry in the university of Glasgow; but dissatisfied with his qualifications for the former post, he exchanged duties with the professor of medicine, and lectured during the ensuing ten years with much care and success on the institutes of medicine, He was at the same time in large practice as a physician, and devoted the most anxious care to the welfare of his patients. Nevertheless he found time to complete the second achievement in science with which his name remains associated. This is the discovery of what is termed ‘latent heat.' In 1756 he began to meditate on the perplexing slowness with which ice melts, and water is dissipated in boiling. He divined the cause in 1757, and ascertained it in 1761. A large quantity of heat, he found, is consumed in bringing about these changes in the state of aggregation, and is thus rendered insensible to the thermometer. The cause of this disappearance, according to modern theory, is the employment of the absorbed heat in doing work—that is, conferring ‘potential energy' on material particles; in Black’s view it was the formation of a quasi-chemical combination between those particles and the subtle fluid of heat, But this erroneous conception in no way detracted from the importance of his discovery. The decisive experiment of obtaining from water during congelation an amount of heat equal to that expended or rendered ‘latent’ in its liquefaction was performed in December 1761. This quantity s measured at rather more than would have sufficed to raise the temperature of the same weight of water 140° Fahrenheit (accurately 143°). He, however, considerably underestimated the latent heat of steam, fixing it, with his pupil Irvine’s assistance, 9 Oct. 1764, at 750° (later at 810°) instead of 967°. The results of this brilliant investigation not only formed the basis of modern thermal science, but gave the first impulse to Watt's improvements in the steam-engine, and thereby to modern industrial developments. Black read an account of his successful experiments before a literary society in Glasgow, 23 April 1762, and from 1761 downwards carefully taught the doctrine of latent heat in his lectures, dwelling with sedate eloquence on the beneficent effects of the arrangement in checking and regulating the processes of nature. But he published nothing on the subject, and was thus scarcely entitled to complain if his ideas were appropriated with little or no acknowledgment. To the same society he detailed, 28 March 1760, a series of experiments instituted with the object of testing the validity of thermometrical indications. He originated, moreover, the theory of ‘specific heat,’ or of the various thermal ‘capacities’ of different bodies, but committed it to Irvine to work out. Still treading in his master's footsteps, Black became, on Cullen's advancement to a higher post in 1766, professor of medicine and chemistry in the university of Edinburgh. His career thenceforward was exclusively that of a teacher. Restricting his medical practice to a narrow circle of friends, and abandoning all thought of original research, he concentrated his powers upon the effective discharge of his official duties. His success was conspicuous. During above thirty years he inculcated the elements of chemistry upon enthusiastic and continually growing audiences. ‘It could not be otherwise,’ Robison wrote in 1803. ‘His personal appearance and manner were those of a gentleman, and peculiarly pleasing. His voice in lecturing was low, but fine; and his articulation so distinct that he was perfectly well heard by an audience consisting of several hundreds. His discourse was so plain and perspicuous, his illustrations by experiment so apposite, that his sentiments on any subject never could be mistaken, even by the most illiterate; and his instructions were so clear of all hypothesis or conjecture, that the hearer rested on his conclusions with a confidence scarcely exceeded in matters of his own experience’ (Black's Lectures, preface, lxii). His lectures had thus a powerful effect in popularising chemistry; and attendance upon them even came to be a fashionable amusement.
Black was a prominent member of the intellectual society by which Edinburgh was then distinguished. Amongst his intimates were his relative and colleague Adam Ferguson, Hume, Hutton, A. Carlyle, Dugald Stewart, and John Robison. Adam Smith, with whom he knit a close friendship at Glasgow, used to say that ‘no man had less nonsense in his head than Dr. Black.’ He was one of James Watt’s earliest patrons, and kept up a constant correspondence with him, Though grave and reserved, Black was gentle and sincere, and it is recorded of him that he never lost a friend. He was at the same time gifted with a keen judgment of character, and with the power of expressing that judgment in an ‘indelible phrase.' In person he is described as ‘rather above the middle size; he was of a slender make; his countenance was placid, and exceedingly engaging’ (Thomson). As he advanced in years, Robison tells us, he preserved a pleasing air of inward contentment. Graceful and unaffected in manner, ‘he was of most, easy approach, affable, and readily entered into conversation, whether serious or trivial.’ Nor did he disdain elegant accomplishments. In his youth he both sang and played tastefully upon the flute. He had talent for painting, and ‘figure of every kind excited his attention . . even a retort or a crucible was to his eye an example of beauty or deformity.' But love of propriety, the same authority informs us, was his leading sentiment, Indeed, his mind was so nicely balanced as to be deficient in motive power. He had all the faculties of invention, but lacked fervour to keep them at work. Hence the slackness with which he pursued discoveries which his genius, as it were, compelled him to make.
A perhaps more prevailing reason for his inaction was the weakness of his constitution. The least undue strain, whether physical or mental, produced spitting of blood, and it was only by the most watchful precautions that he maintained unbroken, though feeble, health. From 1793, however, it visibly declined, and he led, more and more completely, the life of a valetudinarian. In 1795 Charles Hope was appointed his coadjutor in his professorship; in 1797 he lectured for the last time. The end came 6 Dec. 1799 (Dr. G. Wilson, in Proc. Royal Soc. Edinburgh, ii. 238), just in the way he had often desired. ‘Being at table,’ Ferguson relates, ‘with his usual fare, some bread, a few prunes, and a measured quantity of milk diluted with water, and having the cup in his hand when the last stroke of the pulse was to be given, he appeared to have set it down on his knees, which were joined together, and in the action expired without spilling a drop, as if an experiment had been purposely made to evince the facility with which he departed.’ The provisions of his will curiously illustrated the just but cold precision of his modes of thought. He divided his property, without specification of its amount, into 10,000 portions, ‘parcelled to a numerous list of relatives, in shares, in numbers or fractions of shares, according to the degree in which they were proper objects of his care or solicitude.’ He was never married. but lived on the best terms with his family. His morals were irreproachable, his habits abstemious, his frugality was free from parsimony. Indifferent to fame, he disliked the publicity of authorship, and never could be induced to vindicate claims which his friends held to be, in many quarters, encroached upon. He enjoyed, nevertheless, a unique reputation. Fourcroy called him ‘the Nestor of the chemistry of the eighteenth century’ (Hoefer, Hist. de la Chimie, ii. 353); Lavoisier acknowledged himself his disciple, Black, on his side, while professing the highest admiration for Lavoisier's genius, and admitting his discoveries, intensely disliked what he regarded as his premature generalisations. ‘Chemistry,' he observed, ‘is not yet a science. We are very far from the knowledge of first principles. We should avoid everything that has the pretensions of a full system’ (Lectures, note xxvi.) This philosophic caution was eminently characteristic.
Amongst other honours Black was elected member of the Paris and St. Petersburg Academies of Sciences, of the Society of Medicine of Paris, as well as of the Royal Society of Edinburgh, and of the Royal College of Physicians, He was, besides, first physician, to his majesty for Scotland. It is worth notice that he made, in 1767, the first attempt to inflate a balloon with hydrogen (Ed. Encycl. iii. (pt. ii.) 553). His lectures were published by Robison in 1803 from notes found after his death, eked out by those of his hearers, in two quarto volumes, entitled 'Lectures on the Elements of Chemistry, delivered in the University of Edinburgh.' A German translation by Crell appeared at Hamburg in 1804–5, and again in 1818, in four vols. 8vo. Black communicated to the Royal Society of London a paper 'On the supposed Effect of Boiling upon Water in disposing it to freeze more readily, ascertained by Experiment’ (Phil. Trans. lxv. 124) and to that of Edinburgh ‘An Analysis of the Waters of some Hot Springs in Iceland’ (Trans. R. Soc. Ed. iii. 95). Two letters by him on chemical subjects were published, one by Lavoisier in the ‘Annales de Chimie,' the other by Crell in his 'Collections' for 1783.
[Ferguson, Trans. R. Soc. Ed. v. 101; (Hist. of Soc.); Robison's Pref. to Black's Lectures; Thomas Thomson, M.D., Brewster's Ed. Encycl. iii. (pt. ii,), 548; Sir A. Grant's University of Edinburgh, ii. 395; Bibl. Britannique, xxviii. 133, 324 (1805); Phil. Mag. x. 157 (1801); Ann. Phil. iii. 324; Bromley's Cat. of Engraved Portraits, 383.]