This opinion was attacked by Haller, and defended by M. Fougeroux, nephew of M. Duhamel; but it is not our business here to inquire how far correct.
One of the most important of M. Duhamel’s papers, which will secure his name a proud station in the annals of chemistry, is that which was inserted in the Memoirs of the Academy for 1737, in which he shows that the base of common salt is a true fixed alkali, different in some respects from the alkali extracted from land plants, and known by the name of potash, but similar to that obtained by the incineration of marine plants. We are surprised that a fact so simple and elementary was disputed by the French chemists, and rather indicated than proved by Stahl and his followers. The conclusions of Duhamel were disputed by Pott; but finally confirmed by Margraaf. M. Duhamel carried his researches further, he wished to know if the difference between potash and soda depends on the plants that produce them, or on the nature of the soil in which they grow. He sowed kali at Denainvilliers, and continued his experiments during a great number of years. M. Cadet, at his request, examined the salts contained in the ashes of the kali of Denainvilliers. He found that during the first year soda predominated in these ashes. During the successive years the potash increased rapidly, and at last the soda almost entirely disappeared. It was obvious from this, that the alkalies in plants are drawn at least chiefly from the soil in which they vegetate.
The memoirs of M. Duhamel on ether, at that time almost unknown, on soluble tartars, and on lime, contain many facts both curious and accurately stated; though our present knowledge of these bodies is so much greater than his—the new facts ascertained respecting them are so numerous and important, that the contributions of this early experimenter, which probably had a considerable share in the success of subsequent investigations, are now almost forgotten. Nor would many readers bear patiently with an attempt to enumerate them.
There is a curious paper of his in the Memoirs of the Academy for 1757. In this he gives the details of a spontaneous combustion of large pieces of cloth soaked in oil and strongly pressed. Cloth thus prepared had often produced similar accidents. Those who were fortunate enough to prevent them, took care to conceal the facts, partly from ignorance of the real cause of the combustion, and partly from a fear that if they were to state what they saw, their testimony would not gain credit. If the combustion had not been prevented, then the public voice would have charged those who had the care of the cloths with culpable negligence, or even with criminal conduct. The observation of M. Duhamel, therefore, was useful, in order to prevent such unjust suspicions from hindering those concerned from taking the requisite precautions. Yet, twenty years after the publication of his paper, two accidental spontaneous combustions, in Russia, were ascribed to treason. The empress Catharine II. alone suspected that the combustion was spontaneous, and experiments made by her orders fully confirmed the evidence previously advanced by the French philosopher.
One man alone would have been insufficient for all the labours undertaken by M. Duhamel; but he had a brother who lived upon his estate at Denainvilliers (the name of which he bore), and divided his time between the performance of benevolent actions and studying the operations of nature. M. Denainvilliers prosecuted in his retreat the observations and experiments intrusted by his brother to his charge. Thus in fact the memoirs of Duhamel exhibit the assiduous labours of two individuals, one of whom contentedly remained unknown to the world, satisfied with the good which he did, and the favours which he conferred upon his country and the human race.
The works of M. Duhamel are very voluminous, and are all written with the utmost plainness. Every thing is elementary, no previous knowledge is taken for granted. His writings are not addressed to philosophers, but to all those who are in quest of practical knowledge. He has been accused of diffuseness of style, and of want of correctness; but his style is simple and clear; and as his object was to inform, not philosophers, but the common people, greater conciseness would have been highly injudicious.
Neither he nor his brother ever married, but thought it better to devote their undivided attention to study. Both were assiduous in no ordinary degree, but the ardour of Duhamel himself continued nearly undiminished till within a year of his death; when, though he still attended the meetings of the academy, he no longer took the same interest in its proceedings. On the 22d of July, 1781, just after leaving the academy, he was struck with apoplexy, and died after lingering twenty-two days in a state of coma.
He was without doubt one of the most eminent men of the age in which he lived; but his merits as a chemist will chiefly be remembered in consequence of his being the first person who demonstrated by satisfactory evidence the peculiar nature of soda, which had been previously confounded with potash. His merits as a vegetable physiologist and agriculturist were of a very high order.
Peter Joseph Macquer was born at Paris, in 1718. His father, Joseph Macquer, was descended from a noble Scottish family, which had sacrificed its property and its country, out of attachment to the family of the Stuarts.183 Young Macquer made choice of medicine as a profession, and devoted himself chiefly to chemistry, for which he showed early a decided taste. He was admitted a member of the Academy of Sciences in the year 1745, when he was twenty-seven years of age. Original researches in chemistry, the composition of chemical elementary works, and the study of the arts connected with chemistry, occupied the whole remainder of his life.
His first paper treated of the effect produced by heating a mixture of saltpetre and white arsenic. It was previously known, that when such a mixture is distilled nitric acid comes over tinged with a blue colour; but nobody had thought of examining the residue of this distillation. Macquer found it soluble in water and capable of crystallizing into a neutral salt composed of potash (the base of saltpetre), and an acid into which the arsenic was changed by the nitric acid communicating oxygen to it.
Macquer found that a similar salt might be obtained with soda or ammonia for its base. Thus he was the first person who pointed out the existence of arsenic acid, and ascertained the properties of some of the salts which it forms. But he made no attempt to obtain arsenic acid in a separate state, or to determine its properties. That very important step was reserved for Scheele, for Macquer seems to have had no suspicion of the true nature of the salt which he had formed.
His next set of experiments was on Prussian blue. He made the first step towards the discovery of the nature of the principle to which that pigment owes its colour. Prussian blue had been accidentally discovered by Diesbach, an operative chemist of Berlin, in 1710, but the mode of producing it was kept secret till it was published in 1724, by Dr. Woodward in the Philosophical Transactions. It consisted in mixing potash and blood together, and heating the mixture in a covered crucible, having a small hole in the lid, till it ceased to give out smoke. The solution of this mixture in water, when mixed with a solution of sulphate of iron, threw down a green powder, which became blue when treated with muriatic acid: this blue matter was Prussian blue. Macquer ascertained that when Prussian blue is exposed to a red heat its blue colour disappears, and it is converted into common peroxide of iron. Hence he concluded that Prussian blue is a compound of oxide of iron, and of something which is destroyed or driven off by a red heat. He showed that this something possessed the characters of an acid; for when Prussian blue is boiled with caustic potash it loses its blue colour, and if the potash be boiled with successive portions of Prussian blue, as long as it is capable of discolouring them, it loses the characters of an acid and assumes those of a neutral salt, and at the same time acquires the property of precipitating iron from the solutions of the sulphate at once of a blue colour. Macquer ascribed the green colour thrown down, by mixing the blood-lie and sulphate of iron to the potash in the blood-lie, not being saturated with the colouring matter of Prussian blue. Hence a portion of the iron is thrown down in the state of Prussian blue, and another portion in that of yellow oxide of iron: these two being mixed form a green. The muriatic acid dissolves the yellow oxide and leaves the Prussian blue untouched. Macquer, however, did not succeed in determining the nature of the colouring matter; a task reserved for Scheele, whose lot it was to take up the half-finished investigations of Macquer, and throw upon them a new and brilliant light. Macquer thought that this colouring matter was phlogiston. On that account the potash saturated with it, which was employed by chemists to detect the presence of iron by forming with it Prussian blue, was called phlogisticated alkali.
Macquer, conjointly with Baumé, subjected the grains of crude platinum, to which the attention of chemists had been newly drawn, to experiment. Their principle object was to examine its fusibility and ductility. They succeeded in fusing it imperfectly, by means of a burning mirror, and found that the grains thus treated were not destitute of ductility. But upon the whole the experiments of these chemists threw but little light upon the subject. Many years elapsed before chemists were able to work this refractory metal, and to make it into vessels fitted for the uses of the laboratory. For this important improvement, which constitutes an era in chemistry, the chemical world was chiefly indebted to Dr. Wollaston.
In the year 1750 M. Macquer was charged with a commission by the court. There existed at that time in Brittany a man, the Count de la Garaie, who, yielding to a passion for benevolence, had for forty years devoted himself to the service of suffering humanity. He had built an hospital by the side of a chemical laboratory: he took care of the patients in the hospital himself; and treated them with medicines prepared in his laboratory. Some of these were new, and, in his opinion, excellent medicines; and he offered to sell them to government for the service of his hospital. Macquer was charged by government with the examination of these medicines. The project of the Count de la Garaie was to extract the salutary parts of minerals, by a long maceration with neutral salts. Among other things he had prepared a mercurial tincture, by a process which lasted several months: but this tincture was merely a solution of corrosive sublimate in spirit of wine. Such is the history of most of those boasted secrets; sometimes they are chimerical, and sometimes known to all the world, except to those who purchase them.
M. Macquer had the fortune to live at a time when chemistry began to be freed from the reveries of alchymists; but methodical arrangement was a merit still unknown to the elementary chemical books, especially in France, where a residue of Cartesianism added to the natural obscurity of the science, by surcharging it with pretended mechanical explanations. Macquer was the first French chemist who gave to an elementary treatise the same clearness, simplicity, and method, which is to be found in the other branches of science. This was no small merit, and undoubtedly contributed considerably to the rapid improvement of the science which so speedily followed. His elements of chemistry were translated into different languages, especially into English; and long constituted the textbook employed in the different European universities. Dr. Black recommended it for many years in the University of Edinburgh. Indeed, it was only superseded in consequence of the new views introduced into chemistry by Lavoisier, which, requiring a new language to render them intelligible, naturally superseded all the elementary chemical books which had preceded the introduction of that language.
Macquer, during a number of years, delivered regular courses of chemical lectures, conjointly with Baumé. In these courses he preferred that arrangement which appeared to him to require the least preliminary knowledge of chemistry. He described the experiments, stated the facts with clearness and precision, and explained them in the way which appeared to him most plausible, according to the opinions generally received; but without placing much confidence in the accuracy of these explanations. He thought it necessary to theorize a little, to enable his pupils the better to connect the facts and to remember them; and to put an end to that painful state of uncertainty which always results from a collection of facts without any theoretical links to bind them together. When the discoveries of Lavoisier began to shake the foundation of the Stahlian theory, Macquer was old; and it appears from a letter of his, published by Delametherie in the Journal de Physique, that he was alarmed at the prophetic announcements of Lavoisier in the academy that the reign of Phlogiston was drawing towards an end. M. Condorcet assures us that his attachment to theory, by which he means phlogiston, was by no means strong;184 but his own letter to Delametherie rather shows that this statement was not quite correct. How, indeed, could he fail to experience an attachment to opinions which it had been the business of his whole life to inculcate?
Macquer also published a dictionary of chemistry, which was very successful, and which was translated into most of the European languages. This mode of treating chemistry was well suited to a science still in its infancy, and which did not yet constitute a complete whole. It enabled him to discuss the different topics in succession, and independent of each other: and thus to introduce much important matter which could not easily have been introduced into a systematic work on chemistry. The second edition of this dictionary was published just at the time when the gases began to attract the attention of scientific men; when facts began to multiply with prodigious rapidity, and to shake the confidence of chemists in all received theories. He acquitted himself of the difficult task of collecting and stating these new facts with considerable success; and doubtless communicated much new information to his countrymen: for the discoveries connected with the gases originated, and were chiefly made, in England, from which, on account of the revolutionary American war, there was some difficulty of obtaining early information.
M. Hellot, who was commissioner of the counsel for dyeing, and chemist to the porcelain manufacture, requested to have M. Macquer for an associate. This request did much honour to Hellot, as he was conscious that the reputation of Macquer as a chemist was superior to his own. Macquer endeavoured, in the first place, to lay down the true principles of the art of dyeing, as the best method of dissipating the obscurity which still hung over it. A great part of his treatise on the art of dyeing silk, published in the collection of the Academy of Sciences, has these principles for its object. He gave processes also for dyeing silk with Prussian blue, and for giving to silk, by means of cochineal, as brilliant a scarlet colour as can be given to woollen cloth by the same dye-stuff. He published nothing on the porcelain manufacture, though he attended particularly to the processes, and introduced several ameliorations. The beautiful porcelain earth at present used at Sevre, was discovered in consequence of a premium which he offered to any person who could point out a clay in every respect proper for making porcelain.
Macquer passed a great part of his life with a brother, whom he affectionately loved: after his death he devoted himself entirely to his wife and two children, whose education he superintended. He was rather averse to society, but conducted himself while in it with much sweetness and affability. He was fond of tranquillity and independence. Though his health had been injured a good many years before his death, the calmness and serenity of his temper prevented strangers from being aware that he was afflicted with any malady. He himself was sensible that his strength was gradually sinking; he predicted his approaching end to his wife, whom he thanked for the happiness which she had spread over his life. He left orders that his body should be opened after his decease, that the cause of his death might be discovered. He died on the 15th of February, 1784. An ossification of the aorta, and several calculous concretions found in the cavities of the heart, had been the cause of the disease under which he had suffered for several years before his death.
These four chemists, of whose lives a sketch has just been given, were the most eminent that France ever produced belonging to the Stahlian school of chemistry. Baron, Malouin, Rouelle senior, Tillet, Cadet, Baumé, Sage, and several others whose names I purposely omit, likewise cultivated chemistry, during that period, with assiduity and success; and were each of them the authors of papers which deserve attention, but which it would be impossible to particularize without swelling this work into a size greatly beyond its proper limits.
Hilaire-Marin Rouelle, who was born at Caen in 1718, was, however, too eminent a chemist to be passed over in silence. His elder brother, William Francis, was a member of the Academy of Sciences, and demonstrator to Macquer, who gave lectures in the Jardin du Roi. At the death of Macquer, in 1770, Hilaire-Marin Rouelle succeeded him. He devoted the whole of his time and money to this situation, and quite altered the nature of the experimental course of chemistry given in the Jardin du Roi. He was in some measure the author of the chemistry of animal bodies, at least in France. When he published his experiments on the salts of urine, and of blood, he had scarcely any model; and though he committed some considerable mistakes, he ascertained several essential and important facts, which have been since fully confirmed by more modern experimenters. He died on the 7th of April, 1779, aged sixty-one years. His temper was peculiar, and he was too honest and too open for the situation in which he was placed, and for a state of society in which every thing was carried by intrigue and finesse. This is the reason why, in France, his reputation was lower than it ought to have been. It accounts, too, for his never becoming a member of the Academy of Sciences, nor of any of the other numerous academies which at that time swarmed in France. Nothing is more common than to find these unjust decisions raise or depress men of science far above or far below their true standard. Romé de Lisle, the first person who commenced the study of crystals, and placed that study in a proper point of view, was a man of the same stamp with the younger Rouelle, and never on that account, became a member of any academy, or acquired that reputation during his lifetime, to which his laborious career justly entitled him. It would be an easy, though an invidious task, to point out various individuals, especially in France, whose reputation, in consequence of accidental and adventitious circumstances, rose just as much above their deserts, as those of Rouelle, and Romé de Lisle were sunk below.
The spirit which Newton had infused for the mathematical science was so great, that during many years they drew within their vortex almost all the scientific men in Great Britain. Dr. Stephen Hales is almost the only remarkable exception, during the early part of the eighteenth century. His vegetable statics constituted a most ingenious and valuable contribution to vegetable physiology. His hæmastatics was a no less valuable contribution to iatro-mathematics, at that time the fashionable medical theory in Great Britain. While his analysis of air, and experiments on the animal calculus constituted, in all probability, the foundation-stone of the whole discoveries respecting the gases to which the great subsequent progress of chemistry is chiefly owing.
Dr. William Cullen, to whom medicine lies under deep obligations, and who afterwards raised the medical celebrity of the College of Edinburgh to so high a pitch, had the merit of first perceiving the importance of scientific chemistry, and the reputation which that man was likely to earn, who should devote himself to the cultivation of it. Hitherto chemistry in Great Britain, and on the continent also, was considered as a mere appendage to medicine, and useful only so far as it contributed to the formation of new and useful remedies. This was the reason why it came to constitute an essential part of the education of every medical man, and why a physician was considered as unfit for practice unless he was also a chemist. But Dr. Cullen viewed the science as far more important; as capable of throwing light on the constitution of bodies, and of improving and amending of those arts and manufactures that are most useful to man. He resolved to devote himself to its cultivation and improvement; and he would undoubtedly have derived celebrity from this science, had not his fate led rather to the cultivation of medicine. But Dr. Cullen, as the true commencer of the study of scientific chemistry in Great Britain, claims a conspicuous place in this historical sketch.
William Cullen was born in Lanarkshire, in Scotland, in the year 1712, on the 11th of December. His father, though chief magistrate of Hamilton, was not in circumstances to lay out much money on his son. William, therefore, after serving an apprenticeship to a surgeon in Glasgow, went several voyages to the West Indies, as surgeon, in a trading-vessel from London; but tiring of this, he settled, when very young, in the parish of Shotts; and after residing for a short time among the farmers and country people, he went to Hamilton, with a view of practising as a physician.
While he resided near Shotts, it happened that Archibald, Duke of Argyle, who at that time bore the chief political sway in Scotland, paid a visit to a gentleman of rank in that neighbourhood. The duke was fond of science, and was at that time engaged in some chemical researches which required to be elucidated by experiment. Eager in these pursuits, while on his visit he found himself at a loss for some piece of chemical apparatus which his landlord could not furnish; but he mentioned young Cullen to the duke as a person fond of chemistry, and likely therefore to possess the required apparatus. He was accordingly invited to dine, and introduced to his Grace. The duke was so pleased with his knowledge, politeness, and address, that an acquaintance commenced, which laid the foundation of all Cullen’s future advancement.
His residence in Hamilton naturally made his name known to the Duke of Hamilton, whose palace is situated in the immediate vicinity of that town. His Grace being taken with a sudden illness, sent for Cullen, and was highly delighted with the sprightly character, and ingenious conversation of the young physician. He found no difficulty, especially as young Cullen was already known to the Duke of Argyle, in getting him appointed to a place in the University of Glasgow, where his singular talents as a teacher soon became very conspicuous.
It was while Dr. Cullen was a practitioner in Shotts that he formed a connexion with William, afterwards Doctor Hunter, the famous lecturer on anatomy in London, who was a native of the same part of the country as Cullen. These two young men, stimulated by genius, though thwarted by the narrowness of their circumstances, entered into a copartnery business, as surgeons and apothecaries, in the country. The chief object of their contract was to furnish the parties with the means of carrying on their medical studies, which they were not able to do separately. It was stipulated that one of them, alternately, should be allowed to study in whatever college he preferred, during the winter, while the other carried on the common business in his absence. In consequence of this agreement, Cullen was first allowed to study in the University of Edinburgh, for a winter. When it came to Hunter’s turn next winter, he rather chose to go to London. There his singular neatness in dissecting, and uncommon dexterity in making anatomical preparations, his assiduity in study, his mild manners, and easy temper, drew upon him the attention of Dr. Douglas, who at that time read lectures on anatomy and midwifery in the capital. He engaged him as his assistant, and he afterwards succeeded him in the same department with much honour to himself, and advantage to the public. Thus was dissolved a copartnership of perhaps as singular a kind as any that occurs in the annals of science. Cullen was not disposed to let any engagement with him prove a bar to his partner’s advancement in the world. The articles were abandoned, and Cullen and Hunter kept up ever after a friendly correspondence; though there is reason to believe that they never afterwards met.
It was while a country practitioner that young Cullen married a Miss Johnston, daughter of a neighbouring clergyman. The connexion was fortunate and lasting. She brought her husband a numerous family, and continued his faithful companion through all the alterations of his fortune. She died in the summer of 1786.
In the year 1746 Cullen, who had now taken the degree of doctor of medicine, was appointed lecturer on chemistry in the University of Glasgow; and in the month of October began a course on that science. His singular talent for arrangement, his distinctness of enunciation, his vivacity of manner, and his knowledge of the science which he taught, rendered his lectures interesting to a degree which had been till then unknown in that university: he was adored by the students. The former professors were eclipsed by the brilliancy of his reputation, and he had to encounter all those little rubs and insults that disappointed envy naturally threw in his way. But he proceeded in his career regardless of these petty mortifications; and supported by the public, he was more than consoled for the contumely heaped upon him by the ill nature and pitiful malignity of his colleagues. His practice as a physician increased every day, and a vacancy occurring in the chair in 1751, he was appointed by the crown professor of medicine, which put him on a footing of equality with his colleagues in the university. This new appointment called forth powers which he was not before known to possess, and thus served still further to increase his reputation.
At that time the patrons of the University of Edinburgh were eagerly bent on raising the reputation of their medical school, and were in consequence on the look out for men of abilities and reputation to fill their respective chairs. Their attention was soon drawn towards Cullen, and on the death of Dr. Plummer, in 1756, he was unanimously invited to fill the vacant chemical chair. He accepted the invitation, and began his academical career in the College of Edinburgh in October of that year, and here he continued during the remainder of his life.
The appearance of Dr. Cullen in the College of Edinburgh constitutes a memorable era in the progress of that celebrated school. Hitherto chemistry being reckoned of little importance, had been attended by very few students; when Cullen began to lecture it became a favourite study, almost all the students flocking to hear him, and the chemical class becoming immediately more numerous than any other in the college, anatomy alone excepted. The students in general spoke of the new professor with that rapturous ardour so natural to young men when highly pleased. These eulogiums were doubtless extravagant, and proved disgusting to his colleagues. A party was formed to oppose this new favourite of the public. His opinions were misrepresented, it was affirmed that he taught doctrines which excited the alarm of some of the most moderate and conscientious of his colleagues. Thus a violent ferment was excited, and some time elapsed before the malignant arts by which this flame had been blown up were discovered.
During this time of public ferment Cullen went steadily forward; he never gave an ear to the gossip brought him respecting the conduct of his colleagues, nor did he take any notice of the doctrines which they taught. Some of their unguarded strictures on himself might occasionally have come to his ears; but if it was so, he took no notice of them whatever; they seemed to have made no impression on him.
This futile attempt to lower his character being thus baffled, his fame as a professor, and his reputation as a physician, increased daily: nor could it be otherwise; his professional knowledge was always great, and his manner of lecturing singularly clear and intelligible, lively, and entertaining. To his patients his conduct was so pleasing, his address so affable and engaging, and his manner so open, so kind, and so little regulated by pecuniary considerations, that those who once applied to him for medical assistance could never afterwards dispense with it: he became the friend and companion of every family he visited, and his future acquaintance could not be dispensed with.
His private conduct to his students was admirable, and deservedly endeared him to every one of them. He was so uniformly attentive to them, and took so much interest in the concerns of those who applied to him for advice; was so cordial and so warm, that it was impossible for any one, who had a heart susceptible of generous emotions, not to be delighted with a conduct so uncommon and so kind. It was this which served more than any thing else to extend his reputation over every civilized quarter of the globe. Among ingenuous youth gratitude easily degenerates into rapture; hence the popularity which he enjoyed, and which to those who do not well weigh the causes which operated on the students must appear excessive.
The general conduct of Cullen to his students was this: with all such as he observed to be attentive and diligent he formed an early acquaintance, by inviting them by twos, by threes, and by fours at a time to sup with him; conversing with them at such times with the most engaging ease, entering freely with them into the subject of their studies, their amusements, their difficulties, their hopes and future prospects. In this way he usually invited the whole of his numerous class till he made himself acquainted with their private character, their abilities, and their objects of pursuit. Those of whom he formed the highest opinion were of course invited most frequently, till an intimacy was gradually formed which proved highly beneficial to them. To their doubts and difficulties he listened with the most obliging condescension, and he solved them to the utmost of his power. His library was at all times open for their accommodation: in short, he treated them as if they had been all his relatives and friends. Few men of distinction left the University of Edinburgh, in his time, with whom he did not keep up a correspondence till they were fairly established in business. This enabled him gradually to form an accurate knowledge of the state of medicine in every country, and the knowledge thus acquired put it in his power to direct students in the choice of places where they might have an opportunity of engaging in business with a reasonable prospect of success.
Nor was it in this way alone that he befriended the students in the University of Edinburgh. Remembering the difficulties with which he had himself to struggle in his younger days, he was at all times singularly attentive to the pecuniary wants of the students. From the general intimacy which he contracted with them he found no difficulty in discovering those whose circumstances were contracted, or who laboured under any pecuniary embarrassment, without being under the necessity of hurting their feelings by a direct inquiry. To such persons, when their habits of study admitted it, he was peculiarly attentive: they were more frequently invited to his house than others, they were treated with unusual kindness and familiarity, they were conducted to his library and encouraged by the most delicate address to borrow from it freely whatever books he thought they had occasion for; and as persons under such circumstances are often extremely shy, books were sometimes pressed upon them as a sort of task, the doctor insisting upon knowing their opinion of such and such passages which they had not read, and desiring them to carry the book home for that purpose: in short, he behaved to them as if he had courted their company. He thus raised them in the opinion of their acquaintances, which, to persons in their circumstances, was of no little consequence. They were inspired at the same time with a secret sense of dignity, which elevated their minds, and excited an uncommon ardour, instead of that desponding inactivity so natural to depressed circumstances. Nor was he less delicate in the manner of supplying their wants: he often found out some polite excuse for refusing to take money for a first course, and never was at a loss for one to an after course. Sometimes (as his lectures were never written) he would request the favour of a sight of their notes, if he knew that they were taken with care, in order to refresh his memory. Sometimes he would express a wish to have their opinion of a particular part of his course, and presented them with a ticket for the purpose. By such delicate pieces of address, in which he greatly excelled, he took care to anticipate their wants. Thus he not only gave them the benefit of his own lectures, but by refusing to take money enabled them to attend such others as were necessary for completing their course of medical study.
He introduced another general rule into the university dictated by the same spirit of disinterested benevolence. Before he came to Edinburgh, it was the custom of the medical professors to accept of fees for their medical attendance when wanted, even from medical students themselves, though they were perhaps attending the professor’s lectures at the time. But Dr. Cullen never would take a fee from any student of the university, though he attended them, when called on as a physician, with the same assiduity and care as if they had been persons of the first rank who paid him most liberally. This gradually led others to follow his example; and it has now become a general rule for medical professors to decline taking any fees when their assistance is necessary to a student. For this useful reform, as well as for many others, the students in the University of Edinburgh are entirely indebted to Dr. Cullen.
The first lectures which Dr. Cullen delivered in Edinburgh were on chemistry; and for many years he also gave lectures on the cases that occurred in the infirmary. In the month of February, 1763, Dr. Alston died, after having begun his usual course of lectures on the materia medica. The magistrates of Edinburgh, who are the patrons of the university, appointed Dr. Cullen to that chair, requesting that he would finish the course of lectures that had been begun by his predecessor. This he agreed to do, and, though he had only a few days to prepare himself, he never once thought of reading the lectures of his predecessor, but resolved to deliver a new course, which should be entirely his own. Some idea may be formed of the popularity of Cullen, by the increase of students to a class nearly half finished: Dr. Alston had been lecturing to ten; as soon as Dr. Cullen began, a hundred new students enrolled themselves.
Some years after, on the death of Dr. Whytt, professor of the theory of medicine, Dr. Cullen was appointed to give lectures in his stead. It was then that he thought it requisite to resign the chemical chair in favour of Dr. Black, his former pupil, whose talents in that department of science were well known. Soon after, on the death of Dr. Rutherford, professor of the practice of medicine, Dr. John Gregory having become a candidate for this place, along with Dr. Cullen, a sort of compromise took place between them, by which they agreed to give lectures alternately, on the theory and practice of medicine, during their joint lives, the longest survivor being allowed to hold either of the classes he should incline. Unluckily this arrangement was soon destroyed, by the sudden and unexpected death of Dr. Gregory, in the flower of his age. Dr. Cullen thenceforth continued to give lectures on the practice of medicine till within a few months of his death, which happened on the 5th of February, 1790, when he was in the seventy-seventh year of his age.
It is not our business to follow Dr. Cullen’s medical career, nor to point out the great benefits which he conferred on nosology and the practice of medicine. He taught four different classes in the University of Edinburgh, which we are not aware to have happened to any other individual, except to professor Dugald Stewart.
Notwithstanding the important impulse which he gave to chemistry, he published nothing upon that science, except a short paper on the cold produced by the evaporation of ether, which made its appearance in one of the volumes of the Edinburgh Physical and Literary Essays. Dr. Cullen employed Dr. Dobson of Liverpool, at that time his pupil, to make experiments on the heat and cold produced by mixing liquids and solids with each other. Dr. Dobson, in making these experiments, observed that the thermometer, when lifted out of many of the liquids, and suspended a short time in the air beside them, fell to a lower degree than indicated by another thermometer which had undergone no such process. After varying his observations on this phenomenon, he found reason to conclude that it was occasioned by the evaporation of the last drop of liquid which adhered to the bulb of the thermometer; the sinking of the thermometer being always greatest when this instrument was taken out of the most volatile liquids. Dr. Cullen had the curiosity to try whether the same phenomenon would appear on repeating these experiments under the exhausted receiver of an air-pump. To satisfy himself, he put on the plate of the air-pump a glass goblet containing water; and in the goblet he placed a wide-mouthed phial containing sulphuric ether. The whole was covered with an air-pump receiver, having at the upper end a collar of leathers in a brass socket, through which a thick smooth wire could be moved; and from the lower end of this wire, projecting into the receiver, was suspended a thermometer. By pushing down the wire, the thermometer could be dipped into the ether; by drawing it up it could be taken out, and suspended over the phial.
The apparatus being thus adjusted, the air-pump was worked to extract the air. An unexpected phenomenon immediately appeared, which prevented the experiment from being made in the way intended. The ether was thrown into a violent agitation, which Dr. Cullen ascribed to the extrication of a great quantity of air: in reality, however, it was boiling violently. What was still more remarkable, the ether, by this boiling or rapid evaporation, became all of a sudden so cold, as to freeze the water in the goblet around it; though the temperature of the air and of all the materials were at the fifty-fourth degree of Fahrenheit at the beginning of the experiment.
I have been particular in giving an account of this curious phenomenon, as it was the only direct contribution to the science of chemistry which Dr. Cullen communicated to the public. The nature of the phenomenon was afterwards explained by Dr. Black; in addition to Dr. Cullen, a philosopher, whom the grand stimulus which his lectures gave to the cultivation of scientific chemistry in this country, had the important merit of bringing forward.
Joseph Black was born in France, on the banks of the Garonne, in the year 1728: his father, Mr. John Black, was a native of Belfast, but of a Scottish family which had been for some time settled there. Mr. Black resided for the most part at Bordeaux, where he was engaged in the wine trade. He married a daughter of Mr. Robert Gordon, of the family of Hillhead, in Aberdeenshire, who was also engaged in the same trade at Bordeaux. Mr. Black was a gentleman of most amiable manners, candid and liberal in his sentiments, and of no common information. These qualities, together with the warmth of his heart, appear very conspicuous in a series of letters to his son, which that son preserved with the nicest care. His good qualities did not escape the discerning eye of the great Montesquieu, one of the presidents of the court of justice in that province. This illustrious and excellent man honoured Mr. Black with a friendship and intimacy altogether rare; of which his descendants were justly proud.
Long before Mr. Black retired from business, his son Joseph was sent home to Belfast, that he might have the education of a British subject. This was in the year 1740, when he was twelve years of age. After the ordinary instruction at the grammar-school, he was sent, in 1746, to continue his education in the University of Glasgow. Here he studied with much assiduity and success: physical science, however, chiefly engrossed his attention. He was a favourite pupil of Dr. Robert Dick, professor of natural philosophy, and the intimate companion of his son and successor. This young professor was of a character peculiarly suited to Dr. Black’s taste, having the clearest conception, and soundest judgment, accompanied by a modesty that was very uncommon. When he succeeded his father, in 1751, he became the delight of the students. He was carried off by a fever in 1757.
Young Black being required by his father to make choice of a profession, he preferred that of medicine as the most suitable to the general habits of his studies. Fortunately Dr. Cullen had just begun his great career in the College of Glasgow, and having made choice of the field of philosophical chemistry which lay as yet unoccupied before him. Hitherto chemistry had been treated as a curious and useful art; but Cullen saw in it a vast department of the science of nature, depending on principles as immutable as the laws of mechanism, and capable of being formed into a system as comprehensive and as complete as astronomy itself. He conceived the resolution of attempting himself to explore this magnificent field, and expected much reputation from accomplishing his object. Nor was he altogether disappointed. He quickly took the science out of the hands of artists, and exhibited it as a study fit for a gentleman. Dr. Black attended his chemical lectures, and, from the character which has already been given of him, it is needless to say that he soon discovered the uncommon value of his pupil, and attached him to himself, rather as a co-operator and a friend, than a pupil. He was considered as his assistant in all his operations, and his experiments were frequently adduced in the lecture as good authority.
Young Black laid down a very comprehensive and serious plan of study. This appears from a number of note-books found among his papers. There are some in which he seems to have inserted every thing as it took his fancy, in medicine, chemistry, jurisprudence, or matters of taste. Into others, the same things are transferred, but distributed according to their scientific connexions. In short, he kept a journal and ledger of his studies, and has posted his books like a merchant. What particularly strikes one in looking over these books, is the steadiness with which he advanced in any path of knowledge. Things are inserted for the first time from some present impression of their singularity or importance, but without any allusion to their connexions. When a thing of the same kind is mentioned again, there is generally a reference back to its fellow; and thus the most isolated facts often acquired a connexion which gave them importance.
He went to Edinburgh to finish his medical studies in 1750 or 1751, where he lived with his cousin german, Mr. James Russel, professor of natural philosophy in that university.
It was the good fortune of chemical science, that at this very time the opinions of professors were divided concerning the manner in which certain lithontriptic medicines, particularly lime-water, acted in alleviating the excruciating pains of the stone and gravel. The students usually partake of such differences of opinion: they are thereby animated to more serious study, and science gains by their emulation. This was a subject quite to the taste of young Mr. Black, one of Dr. Cullen’s most zealous and intelligent chemical pupils. It was, indeed, a most interesting subject, both to the chemist and the physician.
All the medicines which were then in vogue as solvents of urinary calculi had a greater or less resemblance to caustic potash or soda; substances so acrid, when in a concentrated state, that in a short time they reduce the fleshy parts of the animal body to a mere pulp. Thus, though they might possess lithontriptic properties, their exhibition was dangerous, if in unskilful hands. They all seemed to derive their efficacy from quicklime, which again derives its power from the fire. It was therefore very natural for them to ascribe its power to igneous matter imbibed from the fire, retained by the lime, and communicated by it to alkalies, which it renders powerfully acrid. Hence, undoubtedly, the term caustic applied to the alkalies in that state, and hence also the acidum pingue of Mayer, which was a peculiar state of fire. It appears from Dr. Black’s note-books, that he originally entertained the opinion, that caustic alkalies acquired igneous matter from quicklime. In one of them he hints at some way of catching this matter as it escapes from lime, while it becomes mild by exposure to the air; but on the opposite blank page is written, “Nothing escapes—the cup rises considerably by absorbing air.” A few pages further on, he compares the loss of weight sustained by an ounce of chalk when calcined, with its loss while dissolved in muriatic acid. Immediately after this, a medical case is mentioned, which occurred in November, 1752. Hence it would appear, that he had before that time suspected the real cause of the difference between limestone and burnt lime. He had prosecuted his inquiry with vigour; for the experiments with magnesia are soon after mentioned.
These experiments laid open the whole mystery, as appears by another memorandum. “When I precipitate lime by a common alkali there is no effervescence: the air quits the alkali for the lime; but it is lime no longer, but C. C. C.: it now effervesces, which good lime will not.” What a multitude of important consequences naturally flowed from this discovery! He now knew to what the causticity of alkalies is owing, and how to induce it or remove it at pleasure. The common notion was entirely reversed. Lime imparts nothing to the alkalies; it only removes from them a peculiar kind of air (carbonic acid gas) with which they were combined, and which prevented their natural caustic properties from being developed. All the former mysteries disappear, and the greatest simplicity appears in those operations of nature which before appeared so intricate and obscure.
Dr. Black had fixed upon this subject for his inaugural dissertation, and was induced, in consequence, to defer applying for his degree till he had succeeded in establishing his doctrine beyond the possibility of contradiction. The inaugural essay was delivered at a moment peculiarly favourable to the advancement of science. Dr. Cullen had been just removed to Edinburgh, and there was a vacancy in the chemical chair in Glasgow: it could not be bestowed better than on such an alumnus of the university—on one who had distinguished himself both as a chemist and an excellent reasoner; for few finer models of inductive investigation exist than are displayed in Black’s essay on quicklime and magnesia. He was appointed professor of anatomy and lecturer on chemistry in the University of Glasgow in 1756. It was a fortunate circumstance both for himself and for the public, that a situation thus presented itself, just at the time when he was under the necessity of settling in the world—a situation which allowed him to dedicate his talents chiefly to the cultivation of chemistry, his favourite science.
When Dr. Black took his degree in medicine, he sent some copies of his essay to his father at Bordeaux. A copy was given by the old gentleman to his friend, the President Montesquieu, who, after a few days called on Mr. Black, and said to him, “Mr. Black, my very good friend, I rejoice with you; your son will be the honour of your name and family.” This anecdote was told Professor John Robison by the brother of Dr. Black.
Thus Dr. Black, while in Glasgow, taught at one and the same time two different classes. He did not consider himself very well qualified to teach anatomy, but determined to do his utmost; but he soon afterwards made arrangements with the professor of medicine, who, with the concurrence of the university, exchanged his own chair for that of Dr. Black.
Black’s medical lectures constituted his chief task while in Glasgow. They gave the greatest satisfaction by their perspicuity and simplicity, and by the cautious moderation of all his general doctrines: and, indeed, all his perspicuity, and all his neatness of manner in exhibiting simple truths, were necessary to create a relish for moderation and caution, after the brilliant prospects of systematic knowledge to which the students had been accustomed by Dr. Cullen, his celebrated predecessor. But Dr. Black had no wish to form a medical school, distinguished by some all-comprehending doctrine: he satisfied himself with a clear account of as much of physiology as he thought founded on good principles, and a short sketch of such general doctrines as were maintained by the most eminent authors, though perhaps on a less firm foundation. He then endeavoured to deduce a few canons of medical practice, and concluded with certain rules founded on successful practice only, but not deducible from the principles of physiology previously laid down. With his medical lectures he does not appear to have been himself entirely satisfied: he did not encourage conversation on the different topics, and no remains of these lectures were to be found among his papers. The preceding account of them was given to Professor Robison by a surgeon in Glasgow, who attended the two last medical courses which Dr. Black ever delivered.
Dr. Black’s reception at Glasgow by the university was in the highest degree encouraging. His former conduct as a student had not only done him credit in his classes, but had conciliated the affection of the professors to a very high degree. He became immediately connected in the strictest friendship with the celebrated Dr. Adam Smith—a friendship which continued intimate and confidential through the whole of their lives. Both were remarkable for a certain simplicity of character and the most incorruptible integrity. Dr. Smith used to say, that no one had less nonsense in his head than Dr. Black; and he often acknowledged himself obliged to him for setting him right in his judgment of character, confessing that he himself was too apt to form his opinion from a single feature.
It was during his residence in Glasgow, between the years 1759 and 1763, that he brought to maturity those speculations concerning the combination of heat with matter, which had frequently occupied a portion of his thoughts. It had long been known that ice has the property of continuing always at the temperature of 32° till it be melted. This happens equally though it be placed in contact with the warm hand or surrounded with bodies many degrees hotter than itself. The hotter the bodies are that surround it, the sooner is it melted; but its temperature during the whole process of melting, continues uniformly the same. Yet, during the whole process of melting, it is constantly robbing the surrounding bodies of heat; for it makes them colder, without acquiring itself any sensible heat.
Dr. Black had some vague notion that the heat so received by the ice, during its conversion into water, was not lost, but was contained in the water. This opinion was founded chiefly on a curious observation of Fahrenheit, recorded by Boerhaave; namely, that water might in some cases be made considerably colder than melting snow, without freezing. In such cases, when disturbed it would freeze in a moment, and in the act of freezing always gave out a quantity of heat. This opinion was confirmed by observing the slowness with which water is converted into ice, and ice into water. A fine winter-day of sunshine is never sufficient to clear the hills of snow; nor is one frosty night capable of covering the ponds with a thick coating of ice. The phenomena satisfied him that much heat was absorbed and fixed in the water which trickles from wreaths of snow, and that much heat emerged from it while water was slowly converted into ice; for during a thaw the melting snow is always colder than the air, and must, therefore, be always receiving heat from it; while, during a frost, the air is always colder than the freezing water, and must therefore be always receiving heat from it. These observations, and many others which it is needless to state, satisfied Dr. Black that when ice is converted into water it unites with a quantity of heat, without increasing in temperature; and that when water is frozen into ice it gives out a quantity of heat without diminishing in temperature. The heat thus combined is the cause of the fluidity of the water. As it is not sensible to the thermometer, Dr. Black called it latent heat. He made an experiment to determine the quantity of heat necessary to convert ice into water. This he estimated by the length of time necessary to melt a given weight of ice, measuring how much heat entered into the same weight of water, reduced as nearly to the temperature of ice as possible during the first half-hour that the experiment lasted. As the ice continued during the whole of its melting at the same temperature as at first, he concluded that it would absorb, every half-hour that the process lasted, as much heat as the water did during the first half hour. The result of this experiment was, that the latent heat of water amounts to 140°; or, in other words, that this heat, if thrown into a quantity of water, equal in weight to that of the ice melted, would raise its temperature 140°.
Dr. Black, having established this discovery in the most incontrovertible manner by simple and decisive experiments, drew up an account of the whole investigation, and the doctrine which he founded upon it, and read it to a literary society which met every Friday in the faculty-room of the college, consisting of the members of the university and several gentlemen of the city, who had a relish for science and literature. This paper was read on the 23d of April, as appears by the registers of the society.
Dr. Black quickly perceived the vast importance of this discovery, and took a pleasure in laying before his students a view of the beneficial effects of this habitude of heat in the economy of nature. During the summer season a vast magazine of heat was accumulated in the water, which, by gradually emerging during congelation, serves to temper the cold of winter. Were it not for this accumulation of heat in water and other bodies, the sun would no sooner go a few degrees to the south of the equator, than we should feel all the horrors of winter. He did not confine his views to the congelation of water alone, but extended them to every case of congelation and liquefaction which he has ascribed equally to the evolution or fixation of latent heat. Even those bodies which change from solid to fluid, not all at once, but by slow degrees, as butter, tallow, resins, owe, he found, their gradual softening to the same absorption of heat, and the same combination of it with the substance undergoing liquefaction.
Another subject that engaged his attention at this time, was an examination of the scale of the thermometer, to learn whether equal differences of expansion corresponded to equal additions or abstractions of heat. His mode was to mix together equal weights of water of different temperatures, and to measure the temperature of the mixture by a thermometer. It is obvious that the temperature must be the exact mean of that of the two portions of water; and that if the expansion or contraction of the mercury in the thermometer be an exact measure of the difference of temperature, a thermometer, so placed, will indicate the exact mean. Suppose one pound of water at 100° to be mixed with one pound of water at 200°, and the whole heat still to remain in the mixture, it is obvious that it would divide itself equally between the two portions of water. The water of 100° would become hotter, and the water of 200° would become colder: and the increase of temperature in the colder portion would be just as much as the diminution of temperature in the hotter portion. The colder portion would become hotter by 50°, while the hotter portion would become colder by 50°. Hence the real temperature, after mixture, would be 150°; and a thermometer plunged into such a mixture, if a true measurer of heat, would indicate 150°. The result of his experiments was, that as high up as he could try by mixing water of different temperatures, the mercurial thermometer is an accurate measurer of the alterations of temperature.
An account of his experiments on this subject was drawn up by him, and read to the literary society of the College of Glasgow, on the 28th of March, 1760. Dr. Black, at the time he made these experiments, did not know that he had been already anticipated in them by Dr. Brooke Taylor, the celebrated mathematician, who had obtained similar results, and had consigned his experiments to the Royal Society, in whose Transactions for 1723 they were published. It has been since found by Coulomb and Petit, that at higher temperatures than 212° the rate of the expansion of mercury begins to increase. Hence it happens that at high temperatures the expansion of mercury is no longer an accurate measurer of temperature. Fortunately, the expansion of glass very nearly equals the increment of that of mercury. The consequence is, that in a common glass-thermometer mercury measures the true increments of temperature very nearly up to its boiling point; for the boiling point of mercury measured by an air-thermometer is 662°: and if a glass mercurial thermometer be plunged into boiling mercury, it will indicate 660°, a difference of only 2° from the true point.
There is such an analogy between the cessation of thermometric expansion during the liquefaction of ice, and during the conversion of water into steam, that there could be no hesitation about explaining both in the same way. Dr. Black immediately concluded that as water is ice united to a certain quantity of latent heat, so steam is water united to a still greater quantity. The slow conversion of water into steam, notwithstanding the great quantity of heat constantly flowing into it from the fire, left no reasonable doubt about the accuracy of this conclusion. In short, all the phenomena are precisely similar to those of the conversion of ice into water; and so, of course, must the explanation be. So much was he convinced of this, that he taught the doctrine in his lectures in 1761, before he had made a single experiment on the subject; and he explained, with great felicity of argument, many phenomena of nature, which result from this vaporific combination of heat. From notes taken in his class during this session, it appears that nothing more was wanting to complete his views on this subject, than a set of experiments to determine the exact quantity of heat which was combined in steam in a state not indicated by the thermometer, and therefore latent, in the same sense that the heat of liquefaction in water is latent.
The requisite experiments were first attempted by Dr. Black, in 1764. They consisted merely in measuring the time requisite to convert a certain weight of water of a given temperature into steam. The water was put into a tin-plate wide-mouthed vessel, and laid upon a red-hot plate of iron, the initial temperature of the water was marked, and the time necessary to heat it from that point to the boiling point noted, and then the time requisite to boil the whole to dryness. It was taken for granted that as much heat would enter into the water during every minute that the experiment lasted, as did during the first minute. From this it was concluded that the latent heat of steam is not less than 810 degrees.
Mr. James Watt afterwards repeated these experiments with a better apparatus and very great care, and calculated from his results that the latent heat of steam is not under 950 degrees. Lavoisier and Laplace afterwards made experiments in a different way, and deduced 1000° as the result of their experiments. The subsequent experiments of Count Rumford, made in a very ingenious manner, so as to obviate most of the sources of error, to which such researches are liable, come very nearly to those of Lavoisier. 1000° therefore, is usually now-a-days adopted as the number which denotes the true latent heat of steam.
Dr. Black continued in the University of Glasgow from 1756 to 1766, much esteemed as an eminent professor, much employed as an able and attentive physician, and much beloved as an amiable and accomplished man, happy in the enjoyment of a small but select society of friends. Meanwhile his reputation as a chemical philosopher was every day increasing, and pupils from foreign countries carried home with them the peculiar doctrines of his courses—so that fixed air and latent heat began to be spoken of among the naturalists of the continent. In 1766 Dr. Cullen, at that time professor of chemistry in Edinburgh, was appointed professor of medicine, and thus a vacancy was made in the chemical chair of that university. There was but one wish with regard to a successor. Indeed, when the vacancy happened in 1756, on the death of Dr. Plummer, the reputation of Dr. Black, who had just taken his degree, was so high, both as a chemist and an accurate thinker and reasoner, that, had the choice depended on the university, he would have been the new professor of chemistry. He had now, in 1766, greatly added to his claim of merit by his important discovery of latent heat; and he had acquired the esteem of all by the singular moderation and scrupulous caution which marked all his researches.
Dr. Black was appointed to the chemical chair in Edinburgh in 1766, to the general satisfaction of the public, but the University of Glasgow suffered an irreparable loss. In this new situation his talents were more conspicuous and more extensively useful. He saw that the case was so, and while he could not but be gratified by the number of students whom the high reputation of Edinburgh, as a medical school, brought together, his mind was forcibly struck by the importance of his duties as a teacher. This led him to form the resolution of devoting the whole of his study to the improvement of his pupils in the elementary knowledge of chemistry. Many of them came to his class with a very scanty stock of previous knowledge. Many from the workshop of the manufacturer had little or none. He was conscious that the number of this kind of pupils must increase with the increasing activity and prosperity of the country; and they appeared to him 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 of his audience, Dr. Black considered as a sacred duty: he resolved, therefore, that plain doctrines taught in the plainest manner, should henceforth employ his chief study. To render his lectures perfectly intelligible they were illustrated by suitable experiments, by the exhibition of specimens, and by the repetition of chemical processes.
To this method of lecturing Dr. Black rigidly adhered, endeavouring every year to make his courses more plain and familiar, and illustrating them by a greater variety of examples in the way of experiment. No man could perform these more neatly or successfully; they were always ingeniously and judiciously contrived, clearly establishing the point in view, and were never more complicated than was sufficient for the purpose. Nothing that had the least appearance of quackery; nothing calculated to surprise and astonish his audience; nothing savouring of a showman or sleight-of-hand man was ever permitted in his lecture-room. Every thing was simple, neat, and elegant, calculated equally to please and to inform: indeed simplicity and neatness stamped his character. It was this that constituted the charm of his lectures, and rendered them so delightful to his pupils. I can speak of them from experience, for I was fortunate enough to hear the last course of lectures which he ever delivered. I can say with perfect truth that I never listened to any lectures with so much pleasure as to his: and it was the elegant simplicity of his manner, the perfect clearness of his statements, and the vast quantity of information which he contrived in this way to communicate, that delighted me. I was all at once transported into a new world—my views were suddenly enlarged, and I looked down from a height which I had never before reached; and all this knowledge was communicated without any apparent effort either on the part of the professor or his pupils. His illustrations were just sufficient to answer completely the object in view, and nothing more. No quackery, no trickery, no love of mere dazzle and glitter, ever had the least influence upon his conduct. He constituted the most complete model of a perfect chemical lecturer that I have ever had an opportunity of witnessing.
The discovery which Dr. Black had made that marble is a combination of lime and a peculiar substance, to which he gave the name of fixed air, began gradually to attract the attention of chemists in other parts of the world. It was natural in the first place to examine the nature and properties of this fixed air, and the circumstances under which it is generated. It may seem strange and unaccountable that Dr. Black did not enter with ardour into this new career which he had himself opened, and that he allowed others to reap the corn after having himself sown the grain. Yet he did take some steps towards ascertaining the properties of fixed air; though I am not certain what progress he made. He knew that a candle would not burn in it, and that it is destructive to life, when any living animal attempts to breathe it. He knew that it was formed in the lungs during the breathing of animals, and that it is generated during the fermentation of wine and beer. Whether he was aware that it possesses the properties of an acid I do not know; though with the knowledge which he possessed that it combines with alkalies and alkaline earths, and neutralizes them, or at least blunts and diminishes their alkaline properties, the conclusion that it partook of alkaline properties was scarcely avoidable. All these, and probably some other properties of fixed air he was in the constant habit of stating in his lectures from the very commencement of his academical career; though, as he never published anything on the subject himself, it is not possible to know exactly how far his knowledge of the properties of fixed air extended. The oldest manuscript copy of his lectures that I have seen was taken down in writing in the year 1773; and before that time Mr. Cavendish had published his paper on fixed air and hydrogen gas, and had detailed the properties of each. It was impossible from the manuscript of Dr. Black’s lectures to know which of the properties of fixed air stated by him were discovered by himself, and which were taken from Mr. Cavendish.
This languor and listlessness, on the part of Dr. Black, is chiefly to be ascribed to the delicate state of his health, which precluded much exertion, and was particularly inconsistent with any attempt at putting his thoughts down upon paper. Hence, probably, that carelessness about posthumous fame, and that regardlessness of reputation, which, however it may be accounted for from bodily ailment, must still be considered as a blemish. How differently did Paschal act in a similar state of health! With what energy did he exert himself in spite of bodily ailment! But the tone of his mind was quite different from that of Dr. Black. Gentleness, diffidence, and perhaps even slowness of apprehension, were the characteristic features by which the latter was distinguished.
There is an anecdote of Black which I was told by the late Mr. Benjamin Bell, of Edinburgh, author of a well-known system of surgery, and he assured me that he had it from the late Sir George Clarke, of Pennicuik, who was a witness of the circumstance related. Soon after the appearance of Mr. Cavendish’s paper on hydrogen gas, in which he made an approximation to the specific gravity of that body, showing that it was at least ten times lighter than common air, Dr. Black invited a party of his friends to supper, informing them that he had a curiosity to show them. Dr. Hutton, Mr. Clarke of Elden, and Sir George Clarke of Pennicuik, were of the number. When the company invited had assembled, he took them into a room. He had the allentois of a calf filled with hydrogen gas, and upon setting it at liberty, it immediately ascended, and adhered to the ceiling. The phenomenon was easily accounted for: it was taken for granted that a small black thread had been attached to the allentois, that this thread passed through the ceiling, and that some one in the apartment above, by pulling the thread, elevated it to the ceiling, and kept it in this position. This explanation was so probable, that it was acceded to by the whole company; though, like many other plausible theories, it turned out wholly unfounded; for when the allentois was brought down no thread whatever was found attached to it. Dr. Black explained the cause of the ascent to his admiring friends; but such was his carelessness of his own reputation, and of the information of the public, that he never gave the least account of this curious experiment even to his class; and more than twelve years elapsed before this obvious property of hydrogen gas was applied to the elevation of air-balloons, by M. Charles, in Paris.
The constitution of Dr. Black had always been exceedingly delicate. The slightest cold, the most trifling approach to repletion, immediately affected his chest, occasioned feverishness, and if the disorder continued for two or three days, brought on a spitting of blood. In this situation, nothing restored him to ease, but relaxation of thought, and gentle exercise. The sedentary life to which study confined him, was manifestly hurtful; and he never allowed himself to indulge in any investigation that required intense thought, without finding these complaints increased.
Thus situated, Dr. Black was obliged to be a contented spectator of the rapid progress which chemistry was making, without venturing himself to engage in any of the numerous investigations which presented themselves on every side. Such indeed was the eagerness with which chemistry was at that time prosecuted, and such the passion for discovery, that there was some risk that his undoubted claim to originality and priority in his own great discoveries, might be called in question, and even rendered doubtful. His friends at least were afraid of this, and often urged him to do justice to himself, by publishing an account of his own discoveries. He more than once began the task; but was so nice in his notions of the manner in which it should be executed, that the pains he took in forming a plan of the work never failed to affect his health, and oblige him to desist. It is known that he felt hurt at the publication of several of Lavoisier’s papers, in the Mémoires de l’Académie, without any allusion whatever to what he himself had previously done on the same subject. How far Lavoisier was really culpable, and whether he did not intend to do full justice to all the claims of his predecessors, cannot now be known; as he was cut off in the midst of his career, while so many of his scientific projects remained unexecuted. From the posthumous works of Lavoisier, there is some reason for believing that if he had lived, he would have done justice to all parties; but there is no doubt that Dr. Black, in the mean time, thought himself aggrieved, and that he formed the intention of doing himself justice, by publishing an account of his own discoveries; however this intention was thwarted and prevented by bad health.
No one contributed more largely to establish, to support, and to increase, the high character of the medical school in the University of Edinburgh than Dr. Black. His talent for communicating knowledge was not less eminent than his faculty of observation. He soon became one of the principal ornaments of the university; and his lectures were attended by an audience which continued increasing from year to year for more than thirty years. His personal appearance and manners 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. While in Glasgow, he had practised extensively as a physician; but in Edinburgh he declined general practice, and confined his attendance to a few families of intimate and respected friends. He was, however, a physician of good repute in a place where the character of a physician implied no common degree of liberality, propriety, and dignity of manners, as well as of learning and skill.
Such was Dr. Black as a public man. While young, his countenance was comely and interesting; and as he advanced in years, it continued to preserve that pleasing expression of inward satisfaction which, by giving ease to the beholder, never fails to please. His manners were simple, unaffected, and graceful; he was of the most easy approach, affable, and readily entered into conversation, whether serious or trivial: for he was not merely a man of science, but was well acquainted with the elegant accomplishments. He had an accurate musical ear, and a voice which would obey it in the most perfect manner; he sang and performed on the flute with great taste and feeling; and could sing a plain air at sight, which many instrumental performers cannot do. Music was his amusement in Glasgow; after his removal to Edinburgh he gave it up entirely. 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 talents of a historical painter. Figure indeed, of every kind, attracted his attention; in architecture, furniture, ornament of every sort, it was never a matter of indifference to him. Even a retort, or a crucible, was to his eye an example of beauty, or deformity. 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 different habits and pursuits felt in Dr. Black’s company and conversation.