(16 Apr 1728 - 6 Dec 1799)
born a.d. 1728.—died a.d. 1799.
from Lives of Eminent and Illustrious Englishmen (1837)
Oil portrait (c.1770) by David Martin. (source)
[p.272] The foundation of philosophical chemistry was laid in Britain by Dr Cullen. Until about the year 1730, chemistry, in this country at least, was little else than the art of preparing medicines; and the only business of its public professors was to impart to medical students some little knowledge of the principal chemical agents and their action, with an exclusive view to the methods of preparing the different articles of the pharmacopoeia. Dr Cullen's chemical prelections in the college of Glasgow first conferred something like the dignity of a science upon chemistry; and it was his lectures that first incited and directed Black to that course of research which ended in the establishment of the great doctrine of latent heat, and those discoveries respecting lime and magnesia which conducted other chemists to the true theory of gases.
Joseph Black was born of British parents at Bourdeaux in France, in the year 1728. He spent in Bourdeaux and its vicinity the first twelve years of his life, at the end of which period he was sent to Belfast, where he received the rudiments of his literary education, which he completed in the university of Glasgow. In the course of his studies, he does not appear to have entered very deeply into the abstract sciences; his predilection for chemistry was early and decided, and he passed his time chiefly in the investigations of experimental philosophy. In making choice of a profession he selected that of medicine, as being the most nearly related to his favourite studies.
He graduated at Edinburgh in 1754. His inaugural dissertation printed on this occasion contains an outline of one of his great discoveries,—the nature of the alkaline earths and the properties of fixed air. It was entitled ‘De Humore acido a cibris orto et Magnesia alba.’ In 1756 he communicated his ideas on this subject at greater length in a paper which he read before a philosophical society in Edinburgh.1 Nothing could exceed in simplicity the methods which our chemist pursued in conducting his researches even at this early period of his investigations. “In the same year,” he says, “in which my first account of these experiments was published, namely 1757, I had discovered that this particular kind of air, attracted by alkaline substances, is deadly to all animals that breathe it by the mouth and nostrils together; but that if the nostrils were kept shut, I was led to think that it might be breathed with safety. I found, for example, that when sparrows died in it in ten or eleven seconds, they would live in it for three or four minutes when the nostrils were shut by melted suet. And I convinced myself, that the change produced on wholesome air by breathing it, consisted chiefly, if not solely, in the conversion of part of it into fixed air. For I found that by blowing through a pipe into lime-water, or a solution of caustic alkali, the lime was precipitated, and the alkali was rendered mild. I was partly led to these experiments by some observations of Dr Hales, [p.273] in which he says that breathing through diaphragms of cloth dipped in alkaline solution, made the air last longer for the purposes of life. In the same year, I found that fixed air is the chief part of the elastic matter which is formed in liquids in the vinous fermentation. Van Helmont had indeed said this, and it was to this that he first gave the name gas silvestre. It could not long be unknown to those occupied in brewing or making wines. But it was at random that he said it was the same with that of the grotto del Cane in Italy—but he supposed the identity, because both are deadly—for he had examined neither of them chemically, nor did he know that it was the air disengaged in the effervescence of alkaline substances with acids. I convinced myself of the fact, by going to a brew-house with two phials, one filled with distilled water, and the other with lime-water. I emptied the first into a vat of wort fermenting briskly, holding the mouth of the phial close to the surface of the wort. I then poured some of the lime-water into it, shut it with my finger, and shook it. The lime-water became turbid immediately. Van Helmont says that the dunste, or deadly vapour of burning charcoal, is the same gas silvestre; but this was also a random conjecture. He does not even say that it extinguishes flame; yet this was known to the chemists of his day. I had now the certain means of deciding the question, since, if the same, it must be fixed air. I made several indistinct experiments as soon as the conjecture occurred to my thoughts; but they were with little contrivance or accuracy. In the evening of the same day that I discovered that it was fixed air that escaped from fermenting liquors, I made an experiment which satisfied me. Unfixing the nozzle of a pair of chamber bellows, I put a bit of charcoal, just red hot, into the wide end of it, and then quickly putting it into its place again, I plunged the pipe to the bottom of a phial, and forced the air very slowly through the charcoal, so as to maintain its combustion, but not produce a heat too suddenly for the phial to bear. When I judged that the air of the phial was completely vitiated, I poured lime-water into it, and had the pleasure of seeing it become milky in a moment.”2 The course of investigation thus opened up for the first time was afterwards pursued by Cavendish and Priestley, and undoubtedly conducted them to those brilliant discoveries which have rendered their names immortal in the annals of chemical science.
In the same year, 1756, Dr Black was appointed to the chair of chemistry and anatomy in Glasgow, vacant by the resignation of his preceptor, Cullen. From this period his attention was necessarily much occupied by the routine of teaching. Before the year 1763, however, he had brought his next grand set of experiments and inquiries on the absorption of beat to a conclusion. He removed from Glasgow to Edinburgh in 1766, where he again succeeded Cullen as professor of chemistry. From this period, says his biographer Mr Robison, he “formed the firm resolution of directing his whole study to the improvement of his scholars in the elementary knowledge of chemistry. He saw too many of them with a very scanty stock of previous learning; he had many from the workshop of the manufacturer, who had none at all; and he saw that the number of such hearers must increase with the increasing activity and prosperity of the country: and these appeared to [p.274] him as by no means the least important part of his auditory. To engage the attention of such pupils, and to be perfectly understood by the most illiterate, was therefore considered by Dr Black as his most sacred duty. Plain doctrines, therefore, taught in the plainest manner, must employ his chief study. That no help may be wanting, all must be illustrated by suitable experiments, by the exhibition of specimens, and the management of chemical processes. Nice and abstruse philosophical opinions would not interest such hearers; any doctrines, inculcated in a refined manner, and referring to elaborate disquisitions of others, would not be understood by the major part of an audience of young persons, as yet only beginning their studies. To this resolution Dr Black strictly adhered, endeavouring every year to make his courses more plain and familiar, and illustrating them by a great variety of examples in the way of. experiment. No man could perform these more neatly and successfully. They were always ingeniously and judiciously contrived, clearly establishing the point in view, and never more than sufficed for this purpose. While he scorned the quackery of a showman, the simplicity, neatness, and elegance, with which they were performed, were truly admirable. Indeed the simplex munditiis stamped every thing that he did. I think it was the unperceived operation of this impression that made Dr Black's lectures such a treat to all his scholars. They were not only instructed, but (they knew not how) delighted; and without any effort to please, but solely by the natural emanation of a gentle and elegant mind, co-operating, indeed, with a most perspicuous exhibition of his sentiments, Dr Black became a favourite lecturer; and many were induced, by the report of his students, to attend his courses, without having any particular relish for chemical knowledge, but merely in order to be pleased. This, however, contributed greatly to the extending the knowledge of chemistry; and it became a fashionable part of the accomplishment of a gentleman.”
Dr Black's only publications, subsequent to his Edinburgh appointment, were a paper on the effects of boiling upon water in disposing it to freeze more readily, printed in the ‘London Philosophical Transactions’ for 1774, and an analysis of the water of some hot springs in Iceland, in the ‘Edinburgh Philosophical Transactions’ for 1791. He died in 1799.
Mr Robison has given us an interesting sketch of the personal habits and general demeanour of this illustrious philosopher. “I have already observed,” says he, “that when I was first acquainted with Dr Black, his aspect was comely and interesting. As he advanced in years his countenance continued to preserve that pleasing expression of inward satisfaction, which, by giving ease to the beholder, never fails to please. His manner was perfectly easy, and unaffected, and graceful. He was of most easy approach, affable, and readily entered into conversation, whether serious or trivial. His mind being abundantly furnished with matter, his conversation was at all times pertinent and agreeable; for Dr Black's acquirements were not merely those of a man of science. He was a stranger to none of the elegant accomplishments of life. He therefore easily fell into any topic of conversation, and supported his part in it respectably. He had a fine, or accurate musical ear, and a voice which would obey it in the most perfect manner; for he sung, [p.275] and performed on the flute, with great taste and feeling; and could sing a plain air at sight, which many instrumental performers cannot do. But this was science. Dr Black was a very intelligent judge of musical composition; and I never heard any person express so intelligibly the characteristic differences of some of the national musics of Europe. I speak of Dr Black as I knew him at Glasgow. After his coming to Edinburgh, he gave up most of those amusements. Without having studied drawing, he had acquired a considerable power of expression with his pencil, both in figures and in landscape. He was peculiarly happy in expressing the passions; and seemed, in this respect, to have the talent of a history painter. He had not any opportunities of becoming a connoisseur; but his opinion of a piece of painting, or sculpture, was respected by good judges. Figure, indeed, of every kind, attracted his attention;—in architecture, furniture, ornament of every sort, it was never a matter of indifference. Even a retort or a crucible was to his eye an example of beauty or deformity. His memorandum-books are full of studies (may I call them) of this sort; and there is one drawing of an iron furnace, fitted up with rough unhewn timber, that is finished with great beauty, and would not disgrace the hand of a Woollett. Naturally, therefore, the young ladies were proud of Dr Black's approbation of their taste in matters of ornament. These are not indifferent things; they are features of an elegant mind, and they account for some part of that satisfaction and pleasure which persons of all different habits and pursuits felt in Dr Black's company and conversation. I think that I could frequently discover what was the circumstance of form, &c. in which Dr Black perceived or sought for beauty, —it was some suitableness or propriety; and he has often pointed it out to me, in things where I never could have looked for it. Yet I saw that he was ingeniously in the right. I may almost say, that the love of propriety was the leading sentiment of Dr Black's mind. This was the first standard to which he appealed in all his judgments; and I believe he endeavoured to make it the directing principle of his conduct. Happy is the man whose moderation of pursuits leaves this sentiment in possession of much authority. Seldom are our judgments greatly wrong on this question; but we too seldom listen to them.”
The merits of Black as a chemical philosopher, have been lost sight of amid the brilliant and rapid discoveries of his successors, though, as has been most justly observed, theirs have been only the glories of rearing a system of which he had laid the firm foundations. M. De Luc and the French academicians made an ungenerous attempt to deprive Black of the merits of his great discovery,—the doctrine of latent heat; but his countrymen have successfully vindicated his claim to this most important and fundamental theory. M. Wilcke, secretary to the Stockholm academy, published in the ‘Memoirs’ of that association, for 1772, a paper on the quantity of heat absorbed by snow when it melts. This was, however, just ten years after the publication of Black's discovery. The publications of Lavoisier and Laplace on the same subject were full twenty years later, and Dr Irvine and Dr Crawford had in the interval prosecuted their master's researches with great success, and proved that every substance in nature has a specific heat of its own.
Before Black laid the foundation of a new era in chemistry, the chemists of Europe were universally possessed with a mistaken faith in the [p.276] phlogistic theory of Stahl. According to them, all combustible bodies are compounds,—one of their constituents being what he called phlogiston. During combustion this phlogiston makes its escape, and the other constituents remain behind. A metal, for example, according to the Stahlian theory, is a compound of a calx and phlogiston; and when it is burnt, the phlogiston flies off and the calx remains. But it was very soon discovered that when a metal has undergone combustion, the calx which remains is heavier than the metal was before it was burnt. To meet this difficulty chemists gravely asserted that phlogiston was not merely destitute of weight, but actually endowed with a principle of levity! This phlogiston of Stahl, then, was “evidently no inference from induction, even as modified and altered by his followers; neither was it the hypothesis of any peculiar qualities in the matter of heat: it was the assumption of a substance, different from every other with which we are acquainted, endued with qualities repugnant to the universal properties of matter, and capable of producing every effect which the inventors might wish to explain. Phlogiston was indeed denominated the matter of heat and light; but it might as well have been called the reguline principle; and then, instead of saying that the escape of the matter of heat and light causes the calcination of metals, the followers of Stahl would have said, that the escape of the reguline principle causes the combustion of inflammable bodies. It is evident that no specific effect, no subordination to the laws of chemical affinity, was ever ascribed to the substance which affects our sense with the feeling of heat, until Dr Black, from the most faithful and cautious examination of obvious facts, found that this substance is capable of uniting with bodies, so as not to affect our senses with the peculiar feeling of heat, and yet to produce upon those bodies the most important changes,—in the same manner that an acid, when combined with an alkali, ceases to taste sour, while it destroys the acridity of the alkali, and forms a third body, possessing the noxious qualities of neither. This physical law, discovered by the strictest induction, is applicable to the explanation of an infinite number of phenomena: its operations actually occur in almost every chemical experiment, and its influence is perceived in all the great processes of nature.”
2 Lectures, vol. ii. pp. 87, 88.