THE LIBRARY OF THE UNIVERSITY OF CALIFORNIA PRESENTED BY PROF. CHARLES A. KOFOID AND MRS. PRUDENCE W. KOFOID JUSTUS VON LIZ BIG, Born May 12 th 1803 Died April 18 th 1873.' The Faraday Lecture for THE LIFE-WORK LIEBIG IN EXPERIMENTAL AND PHILOSOPHIC CHEMISTBY ; WITH ALLUSIONS TO HIS INFLUENCE ON THE DEVELOPMENT OF THE COLLATERAL SCIENCES AND OF THE USEFUL ARTS. A DISCOURSE Delivered to the Fellows of the Chemical Society of London in the Theatre of the Royal Institution of Great Britain, on March the 18ta, 1875. BY A. W. ^HOFMANN, F.R.S., V.P.C.S. PROFESSOR OF CHEMISTRY IN THE UNIVERSITY OF BERLIN. ea~xe fj.a.6r)vcrew? Kooyxoi' ayvjpaj TTJJ re cruce'o KO.I O7TTJ KO.I O7TWS. TOIS fie TOIOU'TOIS oufieVoT* epytav /AeAe'rrjjaa Trpoat^ei. Euripides. Eontfon : MACMILLAN AND CO, 1876. L7HL THE FARADAY LECTURE. WE are assembled this evening, friends and fellow- workers, to render our third triennial tribute of homage and gratitude to the memory of Michael Faraday to keep , his great name and example bright among us, and, by so doing, to renew in our minds and hearts the inspiration of his incomparable genius. In organising this periodical celebration of Fara- day's life and labours, the Council of the Chemical Society, mindful of what would have been the wish of the great philosopher himself, has resolved to make these meetings the occasion, not of vain lamentation over an irreparable loss, nor of reiterated eulogies of the great luminary whose setting we deplore, but 'rather of useful surveys of the fields of science he so dearly loved, and of the lives and labours of those illustrious fellow-workers in whose ranks he so con- spicuously shone. As Faraday belonged, from the universality of the benefits conferred by his genius on the human race, not merely to the island of his birth, but to all the civilised countries of the globe, the Council wisely and generously ordained that all nations B 2 4 THE FARADAY LECTURE. should be invited to share with England the happy privilege of rendering homage to the greatest ex- perimental thinker who has ever yet appeared among mankind. FRANCE, worthily represented by the illustrious Dumas, inaugurated, six years ago, the series of these commemorations. In a discourse not less re- markable for the philosophic grasp and grandeur of its conception, than for the harmonious beauty of its flowing periods, he set before us the scientific needs and tendencies of Faraday's time, and the noble labours which placed him foremost among the sowers and reapers of its grand scientific harvests. ITALY followed in the person of Professor Can- nizzaro, who discoursed to us, in language alike profound and eloquent, of the form to be impressed upon the future teaching of chemical science, thus developing a theme, not only in itself of the deepest interest, but one peculiarly appropriate to the occa- sion ; since Faraday, even had he not as a discoverer won imperishable renown, would have ever stood high among the promoters of scientific knowledge by his inapproachable power as an expositor of philo- sophical truth. On the present occasion GERMANY has been invited to take her part in this international tribute to departed genius ; and I shall ever account it one of the most signal honours of my life, that I have been selected to appear before you here, the spokes- man of my country's chemists the interpreter of THE FARADAY LECTURE. 5 German reverence for the greatest physical philo- sopher of the age. I need hardly dwell on my deep sense of the magnitude of the duty I have undertaken to dis- charge, and of my inadequacy to the task of worthily continuing the series of discourses so admirably com- menced by my distinguished predecessors. Conscious of my inferiority to them in the graces of style and the charm of oratory, I have anxiously selected as the theme of my discourse a subject so intrinsically rich in interesting facts and noble lessons, as of itself to command and repay your attention, while claiming from me no eloquence beyond that of a succinct and faithful exposition. Such, Gentlemen, are some of the considerations which have determined me to direct your attention to the labours of one of Faraday's most eminent scientific contemporaries of a master-mind gifted as Faraday's own, of my illustrious teacher and deeply lamented friend JUSTUS VON LIEBIG. In addressing myself to this task, in proceeding to lay before you a sketch of the labours of Liebig, and in touching on some of the characteristic inci- dents of his career, I find myself embarrassed by the very richness of the subject it is my duty to unfold. The many-sided genius of the great discoverer bafEes, with its prolific outpourings, my sense of order and selection ; so that I know not how to dis- 6 THE FARADAY LECTURE. criminate, amidst the manifold treasures he has be- queathed to us, those which claim development on this occasion, from those which, through sheer lack of time, must pass unnoticed. Let me, however, at starting, frankly declare to you my deep-rooted conviction that Liebig's is the name and figure alone fitted to stand beside Fara- day's in the representation of our century to future generations of mankind. Indeed, even while I say this, I am but too well aware that it is hardly for us, their contemporaries, to comprehend, in all its fulness, the towering majesty of these two great men. As those who wander in a mountain-chain cannot appreciate the sky-reaching grandeur of its lofty peaks so well as those who, remotely, from the plains beneath, contemplate its snow-crowned summits, so we, the contemporaries of Faraday and Liebig, cannot perceive the full dignity of their commanding forms, the philosophic pinnacles of this century, as they will hereafter appear to distant generations of posterity. In those days Faraday and Liebig will be looked up to with such reverence as it is ours to offer to the mighty spirits of the past to such giant figures as those of Galileo, Kepler, Newton, and Lavoisier. And as that bright constellation shines on us from the misty darkness of the past, so will the names of Faraday and Liebig, stars of co-equal lustre, throw forward their bright beams on our successors through the far-reaching vista of ages yet to come. THE FARADAY LECTURE. 7 To speak of Liebig only: were we to consider merely the vast number and incalculable importance of the chemical facts which he established, we should have to proclaim him one of the greatest contributors to chemistry at large, that ever has appeared ; while of organic chemistry we could not hesitate to consider him the very source and fountain-head. Yet the discovery of chemical facts has been but apart, and not the greatest, of Liebig's memorable services to our cherished science. By his experimental studies on the correlation and mutual bearing of the facts he discovered, he was led to the conception of general laws, which have shed a flood of light on chemical phenomena of all classes ; illustrating no less the course of inorganic transformations, than the nature of organic compounds and their activities the field he especially cultivated. By the great types of composition which, under the name of radicles, he was the first to reveal, and by the general methods of research resulting from their recognition, he was enabled, not only to trace with a sure and cautious hand the lines of his own lifelong progress, but to map the path of all contemporary research, and shape the course along which, from age to age, so long as chemistry and the collateral sciences continue to ad- vance, they must pursue their development. Speaking, as I do, in the presence of chemical investigators to whom Liebig's methods and appar- atus are so familiar, I need spend no time on the proof of what I have just advanced. Such proof we THE FARADAY LECTURE. find, each one of us, day by day, at every step of our experimental researches. Nor is this hourly help, great as we feel it to be, and masterly as is the hand to which we owe it, by any means all the aid we chemists daily derive from Liebig. It was he who, while placing at our disposal the means, intellectual and material, of prosecuting our researches, was also the first to found in Europe the great institutions for chemical education, by which our minds have been prepared and equipped to employ with advantage the keen weapons, theoretic and instrumental, pro- vided by this great exemplar for our use. It was at the small University of Giessen that Liebig organised the first educational laboratory, properly so called, that was ever founded. The foundation of this school forms an epoch in the his- tory of chemical science. It was here that experi- mental instruction, such as now prevails in our laboratories, received its earliest form and fashion ; and if, at the present moment, we are proud of the magnificent temples raised to experimental science in all our Schools and Universities, let it never be forgotten that they all owe their origin to the proto- type set up by Liebig half a century ago. The new school called around the master, from all nations, a large number of pupils, the elite of the then rising generation of chemists, many of whom are now, in their turn, distinguished masters of our science, having worthily continued the path of discovery opened for them, in their youth, by Liebig. It was THE FARADAY LECTURE. 9 more especially from this country that a great num- ber of young chemists thronged to the school of Giessen ; and I see many before me who not only enjoyed its educational advantages, but have since nobly illustrated their value by the high eminence which they have attained ; and I well know that if their gratitude towards Lie big had to be expressed by acclamation, there is not one of those old pupils present whose voice would be wanting in the general tribute of heartfelt reverence and praise to the great master. This is a point on which, brief as our time may be, I cannot, in common duty, lightly dwell. It is, in fact, one of the most characteristic features of Liebig's influence on the development of modern philosophy, as well as one of the grandest and most generous endowments of his princely heart. Whoever has had the good fortune of attending his lectures, will not easily forget the deep impression of his peculiar style of eloquence. Liebig was not exactly what is called a fluent speaker ; but there was an earnestness, an enthusiasm in all he said, which irresistibly carried away the hearer. Nor was it so much the actual knowledge he imparted which produced this effect, as the wonderful manner in which he called forth the reflective powers of even the least gifted of his pupils. And what a boon was it, after having been stifled by an oppressive load of facts, to drink the pure breath of science such as it flowed from Liebig's lips, what a delight, 10 THE FARADAY LECTURE. after having perhaps received from others a sack full of dry leaves, suddenly, in Liebig's lectures, to see the living growing tree ! Yet not, however, in lecturing was it that Liebig most excelled ; it was by the peripatetic teaching in the laboratory that his greatest successes were achieved. Like all the great generals of every age, Liebig was the spirit as well as the leader of his battalions ; and if he was followed so heartily it was because, much as he was admired, he was loved still more. If I speak somewhat fondly of Liebig, many around me are thinking of him fondly too, for we were alike pupils of his. We remember his fascinating control over every faculty, every sentiment that we pos- sessed ; and we still, in our manhood now, remember how ready we were, as Liebig's young companions in arms, to make any attack at his bidding, and follow wherever he led. We felt then, we feel still, and never while we live shall we forget Liebig's marvellous influence over us ; and if anything could be more astonishing than the amount of work he did with his own hands, it was probably the mountain of chemical toil which he got us to go through. I am sure that he loved us in return. Each word of his carried instruction, every intonation of his voice bespoke regard ; his approval was a mark of honour, and of whatever else we might be proud, our greatest pride of all was in having him for our master. It was our delight, too, to know that we helped him ; that THE FARADAY LECTURE. 11 while we received his lessons, we were also performing his work. The aid he thus obtained, he was too just ever to deny or underrate ; nay, his generosity often attributed to a pupil the whole credit of a success- ful experiment suggested by himself, on the basis of previous trials and discoveries of his own, and of his deductions therefrom. Of our young winnings in the noble playground of philosophical honour, more than half were free gifts to us from Liebig ; and to his generous nature no triumphs of his own brought more sincere delight thaD that which he took in seeing his pupils' success, and in assisting, while he watched their upward struggle. Not only then has Liebig, by his multitudinous discoveries of facts, laid the foundation of organic chemistry ; not only, has he, by his conception of chemical radicles, and his keen insight into chemical analogies, marked out in theory the way of chemical research and discovery for centuries yet to come ; not only has he, in addition to his theoretic guidance, given us the instruments and means of prosecuting the researches by which the domain of chemistry must be enlarged ; but he has also shown us how to keep up the supply of intellectual agents to carry on the work, how human hearts and minds may be pre- pared to prosecute the great warfare against ignor- ance in this field of science, thus furnishing trained soldiers to wield the arms he previously provided. I am sure, Gentlemen, that I shall have your unanimous concurrence when I say that there is no 12 THE FARADAY LECTURE. greater proof of the fecundity of a discoverer's genius than this, that it not only itself raises the curtain from Nature's secrets, and enriches the storehouse of science from the vast treasury of the previously un- known, but that it also endows mankind with the means, intellectual and material, of following on in the same path ; thus taking an anticipated part in Time's ulterior conquests. And to all these great services done to our race by Liebig, may I not truly add the inspiration bequeathed to us by his illustrious example ? Which of us, returning to-morrow to his lonely post in the laboratory, and resuming his obstinate labour in penetrating Nature's stubborn depths, will not feel animated and cheered in his work by the example of such master-minds as those of Faraday and Liebig ? For us chemists more especially, and for our suc- cessors, it will be for years to come a duty, equally imperative and delightful, to work, not only with Liebig's instruments in our hands, but also with his noble spirit in our hearts. And that spirit, as characteristic of Liebig's genius as of Faraday's, led both those great men, as I trust it may lead us, their humble followers, to look beyond the scope of a single sphere of thought ; to pass from the discovery of special instances to the determination of laws governing whole classes of a like nature, and to trace forward those laws in their influence on still wider ranges of phenomena ; not neglecting at the same time their collateral applica- THE FARADAY LECTURE. 13 tions in the improvement of the arts of life, and in the promotion of man's material welfare. Were Faraday the theme of my discourse, I could truly say that no man, more abundantly than he, has enriched, incidentally, the collateral fields of industry by the activity of his pursuit after the abstract laws of nature. And it is but one more of the noble analogies traceable between the careers of these two great men, that Liebig's labours in abstract science have also, like Faraday's, borne copious fruit in many of the useful arts, especially in those whose practice involves chemical transforma- tions. To mention but a few of Liebig's services of this kind, let me remind you of the great industries of acetic acid and the fatty bodies, which were mate- rially elucidated, as well by Liebig's own researches, as by those performed in his laboratory by pupils under his immediate guidance. Among the manu-~ factures thus in some cases brought to a degree of perfection previously unknown, in other cases actually created by him, you will all recollect, as prominent I examples, the industry of the fulminating compounds, that of prussiate of potash, and lastly that of potassic cyanide. Of these, the two former owe to Liebig's labours the very key to their operations ; whilst the latter originated entirely from his investigations in the. cyanogen group. Indeed potassic cyanide, but a few years ago a substance of exclusively scientific interest, is now, since Liebig devised an easy mode 14 THE FARADAY LECTURE. for its preparation, a commercial article of consider- able importance, large quantities of which are used in the various processes of electroplating. As not less intimately, though somewhat differently, rooted in Liebig's researches, may be mentioned the inven- tion of silver-coated mirrors, so superior in effect to the old mercurial reflectors, and now, as we all know, manufactured so extensively. I might greatly prolong this enumeration ; but enough, I think, has been adduced to justify me in stating that Liebig, like Faraday, merited the old classical encomium, illustrans commoda vitce ; and never, in his conscientious benevolence, lost sight of the general interests of his race. o It was not, however, incidentally only, by the collateral development of the industrial arts, that the practically beneficent outcome of Liebig's genius was displayed. In fathoming the deep mysteries of organic chemistry, his penetrating curiosity could not remain indifferent to the yet more profound secrets of biology, that is to say, of life, in its two great forms, vegetal and animal, based, as they both are, in their material development, on processes of chemical change. In the laws of plant-life more especially, Liebig's noble researches threw ray after ray of brilliant light into depths where before the deepest obscurity had reigned. It was Liebig who traced the primor- dial conditions of the nutrition and growth of plants ; and finally established their connection with the THE FARADAY LECTURE. 15 chemical composition of the soil in which they are rooted, and of the air in which their leaves are bathed, as well as with the imponderable forces, especially the sun's light and heat, under whose influence they live. Projecting his view still further in the same direction, he also traced the influence of physical and chemical laws on the second and higher division of biology, namely, that which relates to animal life, its laws and conditions, especially those of the nutri- tion and development of the animal body. It was no doubt in the former of these two high and arduous paths of research that Liebig's labours were crowned with the most perfect success. Under-' 1 taken in the year 1837, at the request then made to him by the British Association for the Advancement of Science, for a Report on the state of our knowl- edge in organic chemistry, they led him to the publication in 1840 of his memorable work, entitled "Chemistry in its Applications to Agriculture and Physiology."* Twenty-two years later (1862), having, during this long interval, studied in minute detail the several questions connected with the sub- ject, he issued his invaluable work, " The Natural * Die Chemie in ihrer Anwendung auf Agricultur und logie, von Justus Liebig, Professor der Chemie an der Univer- sitdt (jriessen. Braunschweig, 1840. Chemistry in its Applications to Agriculture and Physiology. By JUSTUS LIEBIG, M.D., Ph.D., F.R.S., M.R.I.A., Professor of Chemistry in the University of Giessen. Edited from the manuscript of the Author, by L YON PL A YF AIR, Ph.D. London, 1840. 16 THE FARADAY LECTURE. Laws of Husbandry ;"* and his researches, as em- bodied in this great work, may truly be described as constituting the first perfect construction of the philosophy of agriculture that had ever appeared up to that date. Had this memorable treatise been Liebig's on]y work, it would have secured to him an imperishable fame, associating him, as it did, with his most illustrious predecessors in chemico-biological inquiry I mean, as you all well know, Lavoisier and Humphry Davy. Two years had scarcely elapsed since the publica- tion of his first treatise on agricultural chemistry, when Liebig issued his memorable work, " Organic Chemistry in its Applications to Physiology and Pathology, "t in which were embodied his first results in the second and superior branch of chemico-bio- logical research, that branch, namely, which brings animal vitality within the scope of nature's general laws ; and from that period (1842) to the time of his * Die Chemie in Hirer Anwendung auf Agricultur und Physio- logie, von Justus Liebig. 1. Theil. Der chemische Process der Erndhrung der Vegetabilien. 2. Theil. Naturgesetze des Feldbaus. Braunschweig, 1862. The English edition of Part II. is entitled, " The Natural Laws of Husbandry," by JUSTUS VON LIEBIG. Edited by JOHN BLYTH, M.D., Professor of Chemistry in Queen's College, Cork. London, 1863. f Die Thierchemie, oder die Organische Chemie in ihrer Anwendung auf Physiologie und Pathologic, von Justus Liebig. Braunschweig, 1842. " Animal Chemistry, or Chemistry in its Applications to Physiology and Pathology." By JUSTUS LIEBIG. Edited from the Author's manuscript, by WILLIAM GREGORY M.D., F.R.S.E. London, 1842. THE FARADAY LECTURE. 17 death (in 1873), this noble theme never ceased to occupy his thoughts. In these three splendid works, each, if I may use the expression, a conqueror's battle-field, Lie big built up new kingdoms on the ruins of empires over- thrown. The vague hypotheses of old days fell, like captured forts, before him ; and, grimly potent as their defences might have seemed, he showed them to be founded, not on solid facts, but on fallacious guesses only. They, one by one, broke down under the severe philosophical analysis to which they were submitted by Lie big, and under the crucial testing by actual experiment which they underwent at his hands. In the study of biology, vegetal and animal, Lie big was the first to disentangle intricacies that had before seemed problems beyond the grasp of human intellect to solve ; and it was one of the grandest results of his philosophical and experimental investigations, that he traced, amidst the multitudi- nous and apparently ever-varying manifestations of life, in its countless modifications of kind and degree, the operation of a few simple laws, physical and chemical, affording, by their determinate combin- ation, the precise and proved conditions of vital de- velopment, nutrition, growth, and perpetuation, from generation to generation, in unaltered individuality. In the vegetal division of these biological re- searches, not one of more profound importance can be referred to, among Lie big's grand achievements, than his clear and well-established recognition of c 18 THE FARADAY LECTURE. the necessity, for plant-growth, of the ingestion of the minute percentage of non- volatile saline ingre- dients which remain as the " ash " of every plant when burnt. To Liebig we owe the now irrefragably established knowledge that each one of these saline ingredients, however minute its percentage-propor- tion in the composition of the vegetal tissue, is as essential to the plant's life and development as is a full supply of the most weighty constituents of its organic mass. And as a corollary of this universal law, he deduced the certain knowledge that these saline ingredients, taken from the soil by food-crops, unfit the land for the further growth of such crops until those saline ingredients, or ash-constituents of the plant's organised tissue have been restored to the field ; a well established law, whence has sprung the most important rule of agricultural economy, namely, that to maintain the fertility of the crop- producing fields, so much ash-ingredient must be annually restored to the ground as the crop, taken from it, has withdrawn. Pressing his investigations further in this direction, Liebig urged eloquently, not upon philosophers only, but also on practical economists, on statesmen, and on the agricultural community at large, the incalculable waste of national resources, arising from our ignorantly treating town-sewage as a worthless refuse, though it is charged with the saline residue of the citizen's food, wastefully diverting it from the land and pouring it down the rivers to the sea. THE FARADAY LECTURE. 19 The Malthusian economists, observing as a fact the growing scarcity of food, but equally ignorant of the cause of the evil, and of the means available for its cure, did not hesitate to predict the unavoidable arrest, at no distant date, of our race's growth and development, " by the ever-increasing pressure of expanding population on the limited means of sub- sistence." But science, meantime, speaking with Liebig's voice, overruled these gloomy forebodings, and showed the collective organism of mankind to be a self-supporting institution. On this momentous subject, with the very existence of humanity at stake, Liebig did not always speak calmly, but he always spoke wisely and well. In language of impassioned eloquence, he protested against the universal impoverishment of the food- producing continents of the globe by this perpetual robbery and waste of the essential conditions of fertility ; and he warned the wealthy population of Great Britain, in particular, that their present reck- less annual waste of the national resources was hurrying them along the downward road to general decay and impoverishment, which not all the British treasures of coal, iron, and other grand elements of power and property would ever suffice to redeem. As a provisional means of postponing, though not of preventing, the arrival of these foreseen calamities, Liebig was led to make one of his most remarkable suggestions of improvements in practical industry, namely, that of manufacturing artificial fertilizing c 2 20 THE FARADAY LECTURE. compounds, rich in the saline or ash-ingredients of plants, and therefore adapted to renew provisionally the fertility of soils exhausted by the annual expor- tation of their ash-containing crops. It is true that the proposal of Lie big's, vast as is the industry to which it has given rise, cannot be of enduring value to mankind, since the artificial restitution of the saline ingredients to the soil must be attended by an annual waste equal to that occasioning the original impoverishment of the soil, and certain, at no distant date, to exhaust the chemical resources at disposal for artificially repairing that waste. Be this, however, as it may, the whole history of philosophical research, and of its influence in the guidance of industry, does not furnish any example of nobler and grander results than those which have ensued, and are still to follow, for the benefit of man- kind, from the splendid generalisation of Liebig's pregnant thought upon this subject. It has supplied to agriculture the fundamental art of life, its main basis as a perdurable art, as an industry no longer liable to extinction by the exhaustion of the soil ; and it has enabled us let me repeat it to secure not merely the continuous regeneration of plants, but also the ceaseless perpetuation of the animal race, including its chieftain, man a chain of incommen- surable importance, whose first link hangs, if I may so speak, from Justus Liebig's hand. In the second division of biology, in that great THE FARADAY LECTURE. 21 branch of science which leads us from the study of the lower life of plants to the higher vitality of animals and man, Liebig's labours effected a revo- lution not less complete and momentous than that which ensued from his researches in agricultural che- mistry. The student of the laws of animal life and of the changes occasioned in normal vital operations by the influence of disease, was, before Liebig's time, but little accustomed to apply the accurate methods of chemical and physical investigation to the complicated problems involved in vital processes ; and when, occasionally, chemical comments were introduced into physiological discussions, they were usually of the most vague and hypothetical de- scription. This disregard of the chemical method was due mainly to two causes : in the first place, to the cir- cumstance that this method had not at that time arrived at the degree of elaboration and perfection which it has since attained ; and secondly, and perhaps chiefly, to the reluctance felt by the in- quirers of that period to divest any processes, how- ever simple, when accomplished within the living organism, of the operation of vital force. This force of vitality was a kind of bugbear, deterring the majority of investigators from engaging in the study of animal chemistry ; since it was generally believed that all manifestations of chemical and physical action were modified and overruled in a most unaccountable manner by this mysterious force. It is true that 22 THE FARADAY LECTURE. many steps towards a salutary change in this view of things had been made long before Lie big took the field. Several of the constituents of the animal eco- nomy had been examined with more or less suc- cess. The physiologists here present will think of Chevreul's classical labours on the fatty bodies of animal origin; of the early investigations by Berze- lius of urine, blood, and bile ; and of Gmelin and Tiedemann's researches as to the nature of diges- tion. Again, some of the crystalline compounds occurring in animal fluids had been correctly analysed. Thus William Prout, as early as 1819, had fixed the formula of urea which is in use at present ; and nine years later, in 1828, Wohler had demonstrated the possibility of building up from its elements this very urea, the formation of which, up to that period, had been supposed to take place exclusively under the influence of vitality, an experiment ever memo- rable, since it removed at a single blow the artificial barrier which had been raised between organic and inorganic chemistry. And to mention another some- what earlier observation of the same discoverer, which, more perhaps than any other, contributed to shape the course of Liebig's researches : Wohler in 1824 had proved that the salts of organic acids, by passing through the animal body, are converted into carbonates, undergoing, in fact, the same change which is effected by their combustion in the open air. It would not be difficult to quote additional interest- ing investigations of animal products and processes ; THE FAB AD AY LECTURE. 23 but the results obtained had remained unconnected. No one had ever ventured to collect these scattered efforts into a focus for the general elucidation of the phenomena of animal life. It was reserved for Liebig to accomplish this arduous task. Amidst the complex and apparently entangled phenomena attending the development and maintenance of animal vitality, Liebig was the first to discern and elucidate the precise and determinate action of chem- ical and physical laws. This great conception, which, before his day, had never illumined physiolo- gical science, germinated in Liebig's mind, was proved and expanded by his experimental investi- gations, and, finally, by his energetic teaching, became established as one of the convictions of our race. It was under auspicious circumstances that the great task was attempted. Liebig was then in the zenith of his intellecual career ; and if his special object had been to prepare himself for this order of inquiry, he could not have selected more appropriate work than that which during the twenty years prev- iously he had been in the habit of performing. The method of analysing organic bodies was at that time already elaborated ; nor had any one chemist then living more experience in its use ; and no one, lastly, was surrounded by a greater number of pupils desir- ous and well qualified to aid him in his researches. Moreover, it was certainly of no small importance, that, at the period in question, Liebig had already 24 THE FARADAY LECTURE. achieved some of his splendid results in the collateral branch of agricultural chemistry ; and if his prelimi- nary studies in the animal physiology of the time had not been carried to the extreme of detail, we may ask whether this was not an additional advan- tage, since it enabled him to proceed, unburthened with observations in many cases doubtful and per- plexing, and untrammelled by the fetters of precon- ceived notions. But let us examine some of Lie big's chemical work in animal physiology. One of the earliest subjects to which Liebig de- voted himself in this department was the question as to the origin of animal heat. After Lavoisier had recognised the analogy between the processes of combustion and respiration, the idea naturally sug- gested itself to his mind that the heat observed in the animal organism must have the same origin as that which is evolved during combustion ; and after- wards, in a paper published jointly with Laplace, these two illustrious philosophers distinctly stated it as their opinion, based upon experiment, that the sensible heat of the animal organism is the combustion- heat of the carbon and hydrogen which, in the form of food, are burnt in the body. The view advanced by Lavoisier and Laplace was subsequently tested by Dulong and Despretz in a series of admirably conducted researches, performed with all the re- sources the advancement of science had meanwh il THE FARADAY LECTURE. 25 placed at their disposal. These physicists proved that a very considerable proportion indeed of the heat observed may be thus explained, but that, at the same time, an appreciable amount (from 10 to 11 p.c.) remains unaccounted for ; and it marks the state of inquiry at this period that, for the purpose of explaining this deficiency, physiologists did not hesi- tate for a moment to invent additional sources of animal heat, such as nervous activity, friction, and electrical phenomena taking place within the living^, organism. By a careful revision of the subject, and by introducing into the calculation of the experi- ments the combustion-heats of carbon and hydrogen as furnished by the latest estimations, Lie big arrived at the determinate conclusion that the deficit which even yet remained is to be attributed to a diminution of temperature, which the animal must have suffered whilst in the ice-calorimeter, an assumption which appears the more legitimate since the belief prevail- ing at one time that the temperature of the animal body is a constant one, might easily have given rise to what now would appear a strange omission in the experiments'. Be this, however, as it may, in summing > up the inquiry, Liebig declares it to be his unalter- able conviction that the whole of the sensible heat of the animal body may be explained by processes of combustion accomplished within the organism. The assumption of sources of animal heat other than chemical now belongs to the past. It is true, that with the mechanical theory of 26 THE FARADAY LECTURE. heat, such as it has been developed by modern physics, for the foundation of all our considerations, the question at issue assumes a much less important aspect ; for even admitting, as we may do, that nervous activity, friction, and electrical phenomena actually give rise to evolution of heat in the animal body, we now know that all these actions are them- selves but intermediate expressions of chemical change resulting eventually in heat. It is certainly a welcome proof of progress that truths, which the inquirers of a previous period had to conquer step by step, have become, as it were, self-evident to us. But if to-day we rejoice to look down from a greater altitude, we certainly shall not cease gratefully to remember those whose labours have contributed to lift us to our higher point of view. In thus studying the evolution of heat by the oxidation or slow combustion of food in the animal organism, a mind like Liebig's could not but be drawn to investigate the nature of food itself, and his high generalising power soon led him to his well-known classification of nutritive substances. Having duly dwelt upon the importance of the mineral constituents of food, the so-called nourish- ing salts which previously had been entirely disre- garded, and the co-operation of which, in the build- ing up the animal body, is not less essential than in the development of the plant, he proceeds to classify food according to the special purposes which THE FARADAY LECTURE. 27 it is to fulfil in the animal economy. " The food of man and animals," he says/ r " consists of two classes of substances essentially different in their composi- tion. The one class (consisting of nitrogenous sub- stances, albumin, etc.), serves in the formation of blood and in building up the various organs of the body; it is called plastic food. The other (con- sisting of non-nitrogenous substances, the fatty bodies, and the so-called carbo-hydrates), resembles ordinary fuel, serving, as it does, in the generation of heat; it is designated by the term respiratory food. Sugar, starch, and gum may be looked upon as modified woody fibre, from which, it is known, they are capable of being formed. Fat, by the quantity of carbon it contains, stands nearest to coal. We heat our body, exactly as we heat a stove, with fuel which, containing the same elements as wood and coal, differs essentially, however, from the latter substances, by being soluble in the juices of the body/' It is not often that new conceptions, so utterly at variance with what had been previously believed, can boast of such rapid and general reception as was accorded to Liebig's classification of nutriment into nitrogenous, or plastic, and non-nitrogenous, or respiratory. Of course this, like all other classifications ever * Ueber die Verwandlung der Krdfte. Sammlung wissenschaft- licher Vortrdge gehalten zu Munclien im Winter, 1858. Braun- schweig, p. 594. 28 THE FARADAY LECTURE. proposed, is not a perfect one ; for it would be diffi- cult to draw an accurate line of demarcation between the two classes. But these imperfections cannot possibly diminish the value of a view which more perhaps, than any other, has contributed to a correct appreciation of the process of animal nutrition. Some objections have been recently raised against Lie big's classification, more especially on physiologi- cal grounds, and it is, therefore, of particular interest to listen to the opinion which one of the most illus- trious physiologists of the day, Theodor von Bi- schoff, has but lately expressed upon this subject.* "These objections/ 7 he says, " undoubtedly correct as they are, have not been able to supplant Liebig's views, nor will they ever be able to do so, for the truth of these views as a whole will always remain ; nor is it possible to deny the great merit they possess of pointing out in the briefest manner the essential differences of the several varieties of food. In the division, classification, and designation of natural objects, and even of historical events, supposing them founded, not on nature but on the requirement of a comprehensive discriminative distinction, the prin- ciple has ever been acknowledged : a potiori fit denominatio ; and it is this principle which justifies Liebig's classification and confers on it its value." To the active prosecution of the study of food * Tli e odor L. W. Bischoff, iiber den Einftuss des Freiherrn Justus von Liebig auf die Entwickelung der Physiologic. Miln- chen, 1874, p. 27. THE FARADAY LECTURE. 29 from the chemical point of view, we are indebted for the rapid development of one of Liebig's finest philosophical conceptions, namely, his theory of the nutrition of animals. According to this theory, the plant holds a position intermediate between the mineral and the animal world. The animal is in- capable of assimilating the compounds stored up in inorganic nature. To render these compounds sub- servient to the purposes of animal life, they have to undergo a preliminary preparation within the living organism of the plant. The simple mineral mole- cules are thus converted into molecules of a higher order, fit to serve in building up and maintaining alive the body of the animal. The main pillar of this theory is the fact established by experiment, that the nitrogenous principles composing the body of the animal, animal albumin, animal fibrin, and animal casein, are identical in composition with the nitrogenous principles found in the organism of the plant, vegetal albumin, vegetal fibrin, and vegetal casein. The similarity of some of these substances, of animal and vegetal albumin, for instance, had even previously been pointed out by Mulder; but cer- tainly it was left to Liebig to prove their identity by analyses performed either by himself or by his pupils. From the body of the animal, the mineral matter organised by the intervention of the plant, after having served the purposes of animal life, returns again to the stores of mineral nature, in order to renew the circulation. 30 THE FARADAY LECTURED I cannot deny myself the pleasure of reminding you of the often-quoted passage in his Familiar Letters on Chemistry * in which Liebig eloquently sets forth his views : " How admirably simple," he says, "after we have acquired a knowledge of this relation between plants and animals, appears to us the process of formation of the animal body, the origin of its blood and of its organs ! The vegetable substances, which serve for the production of blood, contain already the chief constituent of blood ready formed, with all its elements. The nutritive power of vegetable food is directly proportional to the amount of these sanguigenous compounds in it ; and in consuming such food, the herbivorous animal re- ceives the very same substances which, in flesh, sup- port the life of carnivora. " From carbonic acid, water, and ammonia, that is, from the constituents of the atmosphere, with the addition of sulphur and of certain constituents of the crust of the earth, plants produce the blood of animals : for the carnivora consume, in the blood and flesh of the herbivora, strictly speaking, only the vegetable substances on which the latter have fed. These nitrogenised and sulphurised vegetable products, the albuminous or sanguigenous bodies, assume in the stomach of the herbivora the same form and proper- ties as the fibrin of flesh and animal albumin do in the stomach of the carnivora. * Familiar Letters on Chemistry, 3 edit., 1851, Letter xxvi, p. 350. THE FARADAY LECTURE. 31 " Animal food contains the nutritive constituents of plants, stored up in a concentrated form. " A comprehensive natural law connects the de- velopment of the organs of an animal, their growth and increase in bulk, with the reception of certain substances essentially identical with the chief con- stituent of its blood. It is obvious that the animal organism produces its blood only in regard to the form of that fluid, and that nature has denied to it the power of creating blood out of any other sub- stances, save such as are identical, in all essential points, with albumin, the chief constituent of blood. " The animal body is a higher organism, the deve- lopment of which begins with those substances, with the production of which the life of those vegetables which are commonly used for food ends. The various kinds of grain and of plants used for fodder, die as soon as they have produced seeds. Even in perennial plants, a period of existence terminates with the production of their fruit. In the infinite series of organic products which begins with the inorganic food of plants, and extends to the most complex constituents of the nervous system and brain of animals the highest in the scale, we see no blank, no interruption. The nutritive part of the food of animals, that from which the chief material of their blood is formed, is the last product of the productive energy of vegetables." It is impossible to speak of Liebig's achievements 32 THE FARADAY LECTURE. in physiological chemistry without alluding to his doctrine of the origin and function of fat in the animal economy questions which had never been duly considered at the time when he engaged in this line of inquiry. A careful investigation of the conditions under which accumulation of fat is observed in the body, led him to the positive conclusion that it is within the animal organism that the elaboration of fat takes place ; and that the materials consumed in its formation are the carbo-hydrates, such as starch and sugar, &c., which, like the nitrogenous principles also, the animal finds ready prepared and stored for its use within the organism of the plant. The views advanced by Liebig gave rise to a long and animated controversy with some of the lead- ing chemists of France, more especially with Dumas and Boussingault, who contended that the animal received the fat ready formed from the plant. An appeal to experiment, it is well known, has decided the question in favour of Liebig, and it is interesting to note that in this case, as in many others, the most powerful arguments in support of his views were brought forward by his antagonists themselves. " My mill has ever received its best supply of water from my opponents/' Liebig used to say. Their experi- ments proved indeed that the vegetal food of animals contains more fat than had previously been believed ; but an amount nevertheless utterly insufficient to explain the quantity deposited in fattened pigs and geese living entirely on vegetal food. Important THE FARADAY LECTURE. 33 collateral proof of the faculty possessed by the animal economy of transforming sugar into fat was supplied, moreover, by the observation that bees, when fed exclusively on sugar, nevertheless continue to produce their wax, the homology of which with the ordinary fatty substances had been established beyond doubt by Bro die's researches ; and, as if to complete the chain of evidence, Pelouze, in the very nick of time, had demonstrated the transformation, by the inter- vention of cheese-ferment, of sugar into butyric acid, thus experimentally proving the process assumed by Lie big to be accomplished within the organism of the animal. I am not permitted here to develop this subject fully in its various ramifications ; else I should have also to point out the modifications which Liebig's views, as originally proposed, have since undergone, and are likely to undergo still further. The experiments of the French chemists proved that the co-operation of nitrogenous food was so far necessary for the formation of fat, as that the animal system cannot possibly be maintained in its full vigour unless it receives a proper share of each variety of food. Nor did Lie big hesitate to admit that, under certain conditions, nitrogenous food like- wise may be converted into fat ; and he recalls the easy transformation, without the organism, of fibrin, when undergoing putrefaction, into ammonia and the butyric and valeric .acids. Some modern physiolo- gists, as is well known, go even a step further, by assuming that animal fat is entirely derived from D 34 THE FARADAY LECTURE. nitrogenous food, the carbo-hydrates being exclusively employed for the purposes of respiration. Thus it is seen that the discussion on some secondary points of the question is even now going on ; but the main point of Liebig's position, viz., that the fat originates within the animal organism, is no longer doubted by any physiologist. In rapidly reviewing the general outcome of Liebig's labours in physiological chemistry, I cannot do more than allude, in the most cursory manner, to his more special inquiries in this department. His examination of blood ; his long-continued study of the nature of bile, supported by a splendid series of analytical experiments of several of his pupils ; his researches regarding the constitution of the urine of man and of the carnivora, proving the non-exist- ence in it of lactic acid, elucidating for the first time the relation observed between the reaction whether alkaline or acid of the urine, and the nature of the food consumed, and leading him finally to the elabo- ration of his method of determining urea ; and his ever-memorable investigation, in conjunction with Wohler, of uric acid, these researches will ever remain models unsurpassed of experimental inquiry. I must not, however, conclude this account of Liebig's chemico-physiological work without dwelling for a moment on his celebrated memoir on the constitu- ents of the juice of flesh,* teeming, as it does, with * The memoir has been separately published in Germany THE FARADAY LECTURE. 35 brilliant discoveries, and presenting, even in greater abundance perhaps than any of his other papers, that inexhaustible outflow of philosophical inferences, which the fertility of Liebig's mind never failed to elicit from his discoveries. It is to his indefatigable spirit of investigation that we are indebted for the first elaborate analysis of the saline matter in the juice of flesh, the importance of whose mineral con- stituents was scarcely, and is not perhaps even now, sufficiently appreciated. Of the nature also of the organic substances which are present in this juice, very little was known when Liebig undertook their study. Nearly twenty years had elapsed since Chevreul had pointed out the existence of creatine in flesh, but the remarkable discovery of the illus- trious French chemist had not been followed up. Even the composition of creatine had remained unknown. Liebig established its formula, and examined its products of decomposition, creatinine, sarcosine, &c., as well as many other substances occurring in the juice of flesh, which obviously play an important part in the animal economy ; and he thus opened a new lode in organic chemistry, which has since been further extended, and is still being actively worked by many ardent explorers. From tracing Lie big's course through the philo- under the title, Untersuclmngen uber das Fleisch und seine Zube- reitung zum Nahrungsmittel. Heidelberg, 1847. The English translation is entitled, Researches on the Chemistry of Food. By JustusLiebig, M.D. Edited from the manuscript of the Author by William Gregory, M.D. London, 1847. D 2 36 THE FARADAY LECTURE. sophical heights of natural inquiry, we may feel it perhaps a vast descent to touch on the collateral improvements of material arts and industries that were evolved from his purely scientific labours. But I should be negligent in passing unnoticed, that, exactly as his researches into the nature of plant- nutrition and the conditions of economical crop-feed- ing, or agriculture, gave rise to the first conception of that great industry, the manufacture of chemical manures, so also have his inquiries in animal che- mistry, and more especially his investigation of the composition and nutrition of the animal body, not been long without their incidental practical out- growth. Who but knows that it was from Lie big's mouth that our housewives first learnt how to render the full nutritive value of meat available, or how to prepare a broth for invalids, combining the maximum of nourishing effect with the highest degree of diges- tibility ? Who but has heard, that, having carefully 1 studied the nature of woman's milk, he was led to compound his infant food as a substitute for mother's milk, thus becoming the benefactor even of future generations ? Who, lastly, is ignorant that it is owing to Liebig's researches in physiological che- mistry, that the superabundant animal nourishment of the more thinly-peopled quarters of the globe has been rendered accessible to the over-crowded popula- tions of the opposite moiety ; and that a grand commercial movement, uniting, as it were, by new THE FARADAY LECTURE. 37 bonds the two hemispheres, has been created by the organisation of a food industry already colossal, and tending still to expand with incalculable advantage to the inhabitants of Europe, thus lifted beyond the sharp pressure of deficient nourishment, and secured in the abundant supplies of those invigorating food- constituents upon which the bodily and mental energies are alike dependent for their development ? It would be difficult to quote an example of a new article haying been more rapidly and universally received by European society than Liebig's extract of meat. And this is the more to be wondered at since the most opposite views prevailed, and are perhaps still prevailing, regarding its action on the organism. For whilst those were not wanting who, from the large amount of potash-salts present in it, declared this extract to be an absolute poison, the ignorance of Liebig's blind admirers, or the selfish- ness of interested speculators, did not hesitate to recommend it as a true substitute for meat. It is strange how such an opinion could ever have taken root, since the very mode of preparing the extract, the careful separation of the albuminous principles, of gelatin and of fat, sufficiently shows that at best it represents only part of the meat. Liebig's aim, in introducing his extract, was to present in it those meat-constituents which, added in varying propor- tions to vegetal food of various kinds, would confer upon this food in a measure the value of meat, by rendering its composition similar to that of meat. 38 THE FARADAY LECTURE. The true mode of action of extract of meat is not as yet perfectly understood ; it remains uncertain whether, as many believe, its effect is due to agents of digestion which it contains, or to its mineral saline constituents, or to creatine and the other nitrogenous principles present in it. Probably they have all a share in its action ; but, in whatever way it works, the best proof of its efficacy certainly is the eagerness with which, in a comparatively short time, it has been everywhere adopted, and which, at no distant period, will give to extract of meat a diffusion equal to that of tea or coffee, or fermented liquids. The examples I have quoted must have convinced you how varied have been Lie big's contributions to physiological chemistry, and how many the practical advantages that have flowed, incidentally as it were, and by side-long streams, from the fountain of his mighty mind. But, thankfully as we acknowledge the services actually performed, our debt of gratitude to him is equally great, I had almost said greater still, for the impulse which his teaching has exerted upon the course of investigation amongst his con- temporaries, and the guidance his genius has im- pressed upon the progress of discovery ever since. I have dwelt at some length on Lie big's chemico- physiological work, longer, perhaps, than the legiti- mate boundaries of this lecture appear to admit. But engrossed as we are with our own small pursuits, we but too often lose sight of the giants on whose shoulders we are standing. The conviction of the THE FARADAY LECTURE. 39 powerful impetus given to agriculture by Liebig has fairly taken hold of the public mind ; but his labours in the cause of physiology have not won him anything like the full meed of recognition which that part of his life-work has so nobly earned. Reproachfully, but justly, Bis ch off, in the treat- ise already quoted, exclaims : " I do not believe myself mistaken if I hold the opinion that there are not many among the younger generation of physio- logists and medical men who know, or have even a distant notion, how great, I should rather say how immense, the influence of Liebig's researches, of his writings and teachings, has been and is still, not only on physiology and medicine, but on organic science at large. The majority enjoy the advan- tages gained, and rejoice in the progress, without being conscious of the author. They consider as self-evident the facts established by Liebig, the methods and principles of research diffused by his teaching. They believe that it cannot be otherwise, and care but little for him to whom science, and with science they themselves, are indebted for their present position/ 7 We have now, I think, made a fairly complete, though, of necessity, a cursory and brief survey of the general course and scope of Liebig's indefatigable researches ; and we cannot, I feel, but be vividly im- pressed with the numerous and extensive fields of inquiry over which his active intellect ranged. We 40 THE FARADAY LECTURE. have found him most frequently working in the domain of pure chemistry and largely extending the list of its products and processes, the abundance of its experimental facts, the breadth of its theoretic interpretations, and the prolific forecasts afforded by its laws. Sometimes, in the course of these purely chemical researches, we have observed his experi- ments bearing also upon collateral sciences ; and from these, in their turn, he has drawn welcome rays of light for the elucidation of his most cherished branch of research, chemistry proper. At other times we have had occasion to note with admiration how his clear mind, never too abstract in its opera- tions to neglect any means of ameli orating the arts of life, drew even from his most abstruse discoveries the conditions of industrial improvements of the highest material value to mankind. In many, or "in all, of these widely divergent paths, the researches of Liebig, and their splendid results, theoretic and practical, would well repay our detailed examination, and would, I am sure, be of the deepest interest to every one in this hall. But within the brief space of time allotted to this discourse, we could not follow out in detail any of the wide fields laid open and fertilised by Lie big's prodigal mind ; and from so many paths of illustra- tion I must single out some one alone upon which to dwell at present ; nor can the choice which it devolves on me to make be doubtful. I feel that in fixing this choice I have to reflect, THE FARADAY LECTURE. 41 firstly, that Lie big was himself, above and before all things, a chemist ; and, secondly, that the audience I have the honour to address consists, for the most part, of chemists ; while, even of the non-professional friends who favour us with their company as guests, though few may perhaps be actual toilers in the laboratory, the majority are, if I may use the expres- sion, chemists at heart, drawn hither into the society of us chemists by their scientific predilection and sympathy for our special pursuits, and eager, in union with ourselves, to pay the homage of their affectionate gratitude to the greatest chemist of our time. Bound, therefore, as I am, in my selection, by the chain of Time's rigorous restriction, I will ask your permission to confine the remainder of this discourse to that portion of Liebig's life-work which was devoted to pure chemistry, that noble science to which so many here assembled consecrate their lives, and of which the Institution wherein we have met is one of the most memorable temples. In pursuing this plan, I feel that I must plead for the indulgent pardon of those of my audience who, though deeply interested in chemistry, have not made this science the subject of their special study. They will forgive me if, in reminding my brother chemists of some of Liebig's experimental inquiries, I have to make use of names and terms familiar as the alphabet to working chemists, but falling obscurely and harshly upon non-professional 42 THE FARADAY LECTURE. ears. They will, I trust, remember, in my excuse, that the unavoidable incongruities marking the composition of a general audience cannot but impart some tincture of its own diversified character to the discourse which it calls forth and inspires. And feeling, as they must, that a chemist invited by chemists to speak of the chemical work of Liebig is obliged of necessity to discourse in chemical language, they surely will not find fault with him if he allows himself in spirit, to be transported for a while from the popular air of Albemarle Street to the sterner atmosphere of Burlington House. But, even in the comparatively restricted range of chemistry proper, those of my auditors who know the voluminous character of Lie big's contributions to this great domain of science, will best judge to how very few among a total of researches counting by hundreds, our further illustration of Liebig's career must be confined. Indeed, let me remind you that, in the Royal Society's well-known record of scientific papers, Liebig's contributions number no fewer than 317, whereof 283 are by himself alone, and the remaining few by Liebig working in collabor- ation with others. The great majority of these researches relate to chemistry proper. But even this protracted list brings the enumeration of his papers only to the year 1863, i.e., to the date of the Royal Society's record. From that period down to his death in 1873, Liebig, although chiefly working on collateral fields of inquiry, more especially those THE FARADAY LECTURE. 43 of agriculture and physiology, made many and most valuable additions to the series of his chemical papers. Of these papers, indeed, the mere titles would re- quire for their perusal the whole time still at my disposal ; and if, from among their number, I can give time to the detailed examination of some six or seven, I shall have made the closest approach in my power to a typical survey of Liebig's chemical labours. Yet, even with this twofold restriction of our field of choice, the utmost difficulty remains in framing any general principle sufficiently compre- hensive to guide us in selecting from among the vastness and variety of philosophical wealth be- queathed by Liebig's genius for our enrichment : and I am far from confident of obtaining your un- qualified approbation of the few topics which I have ultimately chosen to bring, in some degree of detail, under your notice. And here, Ladies and Gentlemen, permit me to interrupt, for a minute or two, the thread of my discourse, that I may advert in a few grateful words to the kind assistance lent us on this occasion by my friend Mr. Herbert McLeod, in former days successively my pupil and my assistant, now the distinguished Professor of Experimental Science in the Indian College for Civil Engineering. He is with us, as you see, ready to help me in showing to yo-ths of its weight, of uric acid. At that period, however, this last-mentioned source of uric acid appears to have been rather inaccessible, as the THE FARADAY LECTURE. 85 larger species of serpents were then but rarely exhi- bited in Europe ; so that, even in 1823, Vauquelin considered it worth while to give in the Annales de Chimie et Physique a minute description of serpent's solid deposit as a substance rarely seen. Nevertheless, some products of the decomposition of uric acid had even then already been observed. Henry had prepared a pyro-uric acid which, in 1829, was iden- tified by Wohler with cyanuric acid. Brugnatelli and Prout, about 1818, had discovered the so-called purpuric acid, a mixture of murexide with colourless substances; and Brugnatelli had further pointed out the existence of a peculiar soluble compound called by him erythric acid. But the composition and true chemical character of these compounds still remained shrouded in obscurity. This obscurity, it was reserved for Lie big and Wohler to dispel. Engaged together in investi- gations for this purpose, they soon made it manifest that uric acid possesses an interest by no means exclusively physiological ; but that, mainly by reason of the unlimited mutability which is its most charac- teristic quality, it claims, with certainly an equal force, the attention of the chemical philosopher. This liability to chemical change is, indeed, the very fact which, while increasing the difficulty of the inquiry, enabled Liebig and Wohler to reap a harvest of results, such as few chemists ever gathered from a single field of research. Not less than sixteen new and most remarkable bodies were at a single stroke, 86 THE FARADAY LECTURE. that is to say, in the course of this single investi- gation, introduced by Lie big and Wohler into the edifice of chemistry ! And it is certainly noteworthy that only one of these numerous substances has, up to the present date, disappeared again from science, and that of their formulae one only has called for modification. It would be difficult to adduce a proof more striking than this of the skill in manipu- lation, and scrupulous accuracy with which they conducted their experiments. The inquiry has been subsequently resumed by some of the most distin- guished chemists of our time ; and the well-applied exercise of their care and skill has certainly done much to elucidate the subject further. But their collective labours have not resulted in the production of a series of compounds nearly so numerous and interesting as that first made known to us by Liebig and Wohler's united work in this great field. This circumstance lends a particular interest to the consideration of the method they adopted, shown by its abundant outcome to be so advan- tageous. To take, then, a cursory glance at this method of theirs, we may note in general terms, that it consists essentially in alternate oxidation and re- duction. They employ as their oxidising agent nitric acid, more or less dilute, and raised to various degrees of temperature. Under these varied con- ditions uric acid furnishes different products, some of which the inquirers recognise as old acquaintances, such as, for instance, oxalic acid, urea, and allantoin, THE FARADAY LECTURE. 87 the last-mentioned compound, as its name reminds us, being the characteristic constituent of the allantoic liquid of the cow. In others they recognise substances which their predecessors had observed, but failed to elucidate, and of which the composition, centesimal and molecular, still remained to be made out. In the course of their investigations they show that Brugnatelli's so-called erythric acid is an indifferent body which is formed by the molecule of uric acid fixing one molecule of water together with one atom of oxygen (supplied by cold nitric acid) and losing one molecule of urea. This body Liebig and Wohler designate alloxan, and they give proof that it takes part in the formation of most of the uric derivatives. With sulphuretted hydrogen they demonstrate that it yields alloxantin, remarkable for its violet reaction with baryta- water, and that this, by further reduction, is converted into dialuric acid. By treatment with sulphurous acid they show, more- over, that alloxan is changed into thionuric acid, which retains the sulphuric acid formed in the re- action ; and which, by eliminating this sulphuric acid therefrom, they transform into uramile. Alkalies, they proceed to prove, produce alloxanic acid, as also that compound, marked by the simplicity of its com- position, which is called mesoxalic acid. And by treatment with heated nitric acid, alloxan, they further find, yields parabanic and oxaluric acids ; but I will not continue the lengthy enumeration of sub- stances evolved in their energetic pursuit of this 88 THE FARADAY LECTURE. inquiry by Liebig and Wohler. Flying time forbids the protraction of the list, interesting as every member of it unquestionably is to the chemist, and deeply important by the varied associations which they together recall to the memory. Let me, however, before taking leave of this group of bodies, direct your attention yet for a moment to the most beautiful, and at the same time most enig- matical, of all the compounds which owe their origin to uric acid. I allude to murexide, that precursor of rosaniline, forming, like rosaniline, crystals so remark- able for their green metallic lustre, a body whose wonderful tinctorial properties seemed destined to, and for some time actually did, restore the magnificent purple of the ancients. The existence of murexide had been pointed out by Prout and Brugnatelli ; but our information regarding the compound was most scanty and fragmentary when Liebig and Wohler began its investigation ; and it is to these philosophers that we are indebted for the method of obtaining the substance in a perfectly pure condition, as well as for its first analysis, and for the first exact and complete description of its properties. The necessity I am under of compressing into the narrow compass of a few sentences the history of this remarkable group of bodies, altogether precludes me from more than glancing at the masterly interpre- tation of their experiments given by the associated inquirers. Suffice it to say, that Liebig and Wohler looked upon the members of the uric series THE FARADAY LECTURE. 89 as combinations of urea with various groups of elements derived from a hypothetical body called urile, which they assumed to exist, united with urea, in uric acid itself. Other theories of the constitution of the uric group have since been proposed ; but it deserves notice that the view most generally received at present differs from that of Liebig and Wohler only as the theory of substitution differs from the older theory of radicles. Liebig and Wohler con- sidered these substances as compounds of urea with various radicles, whilst we look upon them as urea, for part of whose hydrogen, atomic groups of varying composition have been substituted. In thus rapidly reviewing the derivatives of uric acid, may I be allowed to quote from Liebig and Wo bier's paper upon this subject a passage clearly indicating how distinctly they foresaw the synthetical direction in which organic chemistry was then about to advance. " From these researches," they say/ 5 " " the philo- sophy of chemistry must draw the conclusion that the synthesis of all organic compounds which are not organised, must be looked upon, not merely as probable, but as certain of ultimate achievement. Sugar, salicin, morphine will be artificially prepared. As yet we are ignorant of the road by which this end is to be reached, since the proximate constituents required for building up these substances are not yet * Untersuchungen uber die Natur der Harnsaure. Ann. Chem. Pharm., xxvi, 242. 90 THE FARADAY LECTURE. known to us ; but these the progress of science cannot fail to reveal." In the sketches of Liebig's experimental labours hitherto submitted to you, I have, mindful of the mixed audience I am addressing, avoided as far as possible the use of formulae. Were I strictly to adhere to this plan, I should be obliged to leave unnoticed one of his most important inquiries, one which has materially assisted in shaping the course of chemical thought, and in preparing our present theoretical conceptions. I speak of his researches on the CONSTITUTION OF ORGANIC ACIDS ; which, at the same time, elucidated the composition and ultimately fixed the formulae of some of the substances most frequently occurring in the household of nature. If Liebig and Wohler, in examining oil of bitter almonds and its derivatives, achieved in so short a time such a series of triumphs, their success was in a great measure due to the accuracy of the analytical methods with which science had been just endowed by Liebig. A more extended application of these methods promised a further harvest of results. In this respect the extensive group of organic acids appeared to offer an appropriate field for cultivation. Hence malic, maleic, camphoric, quinic, and meconic acids were successively examined, not invariably with absolute success, since the num- bers obtained did not always agree among themselves, or with the results of subsequent inquirers. Perhaps, THE FARADAY LECTURE. 91 in some cases, it was the rapidity with which one investigation followed another that caused these early failures ; but in most cases they may be traced to the faculty some of the above acids possess of uniting with varying quantities of water, to their tendency, as we now should call it, of forming anhy- drides. The relation between the quantity of water par- ticipating in the formation of an acid and its faculty of forming salts the basicity of an acid was, at that time, a problem completely unsolved. Berzelius felt this difficulty when, in 1833, he represented the citrates by the formula C 4 H 2 4 ,RO, (H = 1, C = 6, = 8), whilst, what was perfectly unintelligible to him, he found citric acid to be, not as he expected, C 4 H 2 4 ,HO, but C 4 H 2 4 ,fHO, corresponding to one-third of the molecule to-day admitted, C 12 H 8 14 , or C 6 H 8 7 in our present notation. Nor was Liebig able entirely to remove the diffi- culty, when, somewhat later, referring to the results of Berzelius, he discussed this peculiar discrepancy between the formulae of citric acid and the citrates. But in the same year (1833) this obscurity was 92 THE FARADAY LECTURE. illumined by a sudden ray of light. Indeed, we find ourselves before Graham's ever- memorable inquiry as to the causes of the varying basicity of phosphoric acid. He traced this variability to the varying quantities of water which can be fixed by phosphoric anhydride. In ordinary phosphoric, or, as we now call it, orthophosphoric acid, this anhydride is united with 3 atoms of water replaceable by bases ; in pyrophosphoric acid with 2 atoms ; and in meta- phosphoric acid with one atom. But how it happened that the same anhydride should in some cases com- bine with 3 atoms, in others with 2, and in others,, lastly, with one atom of water or base, remained un- intelligible so long as chemical thought continued to move in the grooves of the dualistic conception. We now approach the period when Dumas on the one hand, and Laurent on the other, began to sap the foundation of this conception by sketching the first outlines of their substitution theories. The ideas regarding the nature of acids set forth in 1809 by Humphry Davy, and advocated again in 1819 by Dulong, were thus once more brought promi- nently under the notice of chemists. Lie big opened his mind to these ideas, and the result was the publication, in 1837, of a joint note by him and Dumas on the constitution of several polybasic acids, which is so terse and clear that I cannot do better than quote some of its principal passages.* * Note sur la Constitution de quelques Acides. Par MM. Dumas et Liebig. Compt, rend., v, 862. THE FARADAY LECTURE. 93 " The difficulty which the study of citric acid and its salts presents, can be satisfactorily explained only by assuming that the atomic weight of this acid must be trebled, so that in the neutral salts three atoms of base have actually to be admitted. " We thus arrive at the following series : Absolute citric acid; Anhydride in combination with bases Ci2H 5 On Dry acid Ci 2 H 5 Oii,3HO. Crystallised acid 12 H 5 O n ,3HO + 2aq. Barium salt C 12 H 5 Ou,3BaO. Sodium salt C 12 H 5 O n ,3NaO. " Silver salt C 12 H 5 O n ,3AgO." The formulae here quoted are not exactly those which Liebig and Dumas give in their paper : to render them comparable with those previously used for citric acid, I have translated them into the nota- tion originally adopted by Berzelius, differing from that employed at present only in the circumstance of carbon and oxygen figuring in its formulae with half the atomic weights which are to-day admitted. "The question of citric acid settled/' Liebig and Dumas continue, "we have devoted ourselves with lively interest to another inquiry of ^the same order. The formula adopted for tartaric acid no longer expresses all the facts which the examination of that acid has brought to light. According to the analysis of Berzelius, ta.rtaric acid contains C 4 H 2 5 ." " We doubt not the correctness of this formula, 94 THE FARADAY LECTURE. but we have good reason to believe that tartaric acid, like citric acid, is capable of losing water at the expense of its constituents." " Meconic acid presents a similar behaviour. It is obvious that in these cases we have to deal with a new order of phenomena, the study of which appears to lead to the following general rule : Tn the forma- tion of citrates, tartrates, meconates and cyanurates, each oxygen-atom contained in the base which combines with the acid, replaces and eliminates in the form of water an atom of oxygen contained in the acid : hence these acids do not form salts with an excess of base, but salts of the same description as those of phosphoric acid. " Assuming tartaric acid to be a hydracid and doubling its formula, we arrive at the following simplified formulae, which we place in juxtaposition with the more complex expressions previously em- ployed : Berzelius' Liebig and Dumas' formulae. formulae. Anhydrous acid ........ C 4 H 2 5 Hydrated acid .......... C 4 H 2 5 HO C 8 H 2 Oi 2 , H 4 Neutral potash salt ...... C 4 H 2 5 KO C 8 H 2 12 j ^ 2 Cream of tartar ........ | ^jl^KO C sH 2 12 j {C Q 4 H O 25 " It would thus appear that anhydrous tartaric acid does not exist, tartaric acid itself being a hydracid of a new description, formed by the union of the THE FARADAY LECTURE. 95 radicle C 8 H 2 Oi 2 with 4 atoms of hydrogen. In the saline compounds of tartaric acid, these 4 atoms of hydrogen are entirely or partially replaced by an equivalent of metal. " From a comparison of the formulae suggested by Liebig and Dumas for tartaric acid and the tartrates with those we use at present : Tartaric acid C 4 H 2 H 4 O6 Neutral potash salt C4H 2 H 2 K 2 06 Cream of tartar C 4 H 2 H 3 K0 6 Tartar emetic C 4 H 2 SbK0 6 , it is obvious that the former actually coincide with the latter, if the atomic weights of carbon and oxygen be doubled. Moreover, it is with no small interest that we perceive in these expressions the undoubted germ of our modern notion of the non-equivalence of elementary atoms ; for since, in accordance with these expressions, it is the oxygen of the base, which eliminates the hydrogen of the acid, it is clear that the amount of metal replacing a given quantity of hydrogen must vary with the composition of the metallic oxide acting upon the acid ; and that if MO represents the composition of an oxide consisting of 1 atom of metal and 1 atom of oxygen, then the metal M a of an oxide M a 2 , and the metal M b of an oxide M b O 3 , must have the value of 2M and 3M, and therefore of 3 atoms of hydrogen respectively. Indeed in anhydrous tartar emetic, it is the univalent potassium-atom which replaces one atom, and the 96 THE FAEADAY LECTURE. trivalent antimony atom which replaces three atoms of hydrogen in tartaric acid. The inquiry, commenced by Liebig and Dumas jointly was not continued in this form for a long time. The two investigators found it more convenient to work out- the subject separately. Indeed, as early as in the following year (1838), Liebig returned to the question in an elaborate memoir, " On the Constitution of the Organic Acids." In this splendid paper he accurately describes meconic acid and its salts, comenic acid and the comenates, silver citrate and pyrocitric acid (the citraconic acid of the present day), cyanuric acid and the cyanurates, aspartic acid and its silver salt, gallic acid and the gallates, tannic acid, tartaric acid and tartar emetic, racemic, malic and even mucic and pyromucic acids, giving at the same time the full experimental evidence upon which his conclusions as to the nature of these substances are based. The paper more fully developes the views set forth in the joint note with Dumas, which it supports by addi- tional facts and elucidates by new reasonings. Meconic acid, by the analysis of its silver salt, is recognised as tribasic, and comenic acid, in a similar manner, as bibasic, in accordance with the views at present adopted. Indeed the formula advanced by Liebig are, with few exceptions, the same that we admit to-day. It is here that the simple relation, in which, so far as their molecular weights are concerned, the cyanic, Mminic, and cyanuric acids stand to each other, is first pointed out. Particular attention is THE FARADAY LECTURE. 97 paid to the diagnosis of poly basic acids. As a charac- teristic criterion, the faculty possessed by an acid of forming double salts salts containing two metals is adduced. This is a valuable indication, but one, as we now know, by no means absolutely to be relied upon, and, indeed, from the non-existence of a potassio- sodic sulphate, Liebig is led to deny the bibasicity of sulphuric acid, since so unmistakeably attested by overwhelming evidence. On the other hand, the appropriate selection of the saline compounds, from the study of which the basicity of an acid may be safely inferred, is of course a subject on which he dwells with predilection. The silver salts are found to be the most trustworthy guides in fixing the limits of basicity. Many acids, which with potassium form only acid salts, are readily converted into neutral silver salts ; and this behaviour is at the same time brought forward as a most powerful argument in favour of acids being compounds of radicles with hydrogen ; for, only on this assumption, can we understand why silver oxide, which is easily reduced by hydrogen, is fixed by acids in larger proportion than the more difficultly reducible oxide of potassium. That the theory of hydracids advanced by Davy and Dulong involves the necessity of admitting a host of radicles which are not isolated, is not, in Liebig's eyes, an argument against it ; since the supporters of dualism were not less compelled to assume the existence of numerous imaginary bodies, viz., the acid anhydrides, but few of which had been H 98 THE FARADAY LECTURE. discovered at that time. The theory of the hydracids, on the other hand, presented the advantage of col- lecting al] acids and salts under the same point of view, and of satisfactorily explaining why equivalent quantities of sulphuric and chlorhydric acid, when acting upon lime, give rise to the elimination of the same quantity of water. An additional confirmation of this theory is furnished, according to Lie big, by the behaviour of silver sulphocyanate. The dualistic conceptions formulate this compound CyS,AgS, . whilst according to Davy's and Dulong's view it must be written CyS 2 Ag. The latter conception alone explains why sulphuretted hydrogen separates silver sulphide from the com- pound. The dualistic views were defended with great pertinacity by Berzelius, who was inclined to explain the varying basicity of phosphoric acid by assuming an isomerism of the anhydride, and Liebig was thus induced to return once more to the subject, maintaining his views in a letter addressed to Ber- zelius.'* In the latter he says, " We have no proof that the water we expel from an acid by the action of a metallic oxide, is as such contained in it ; all we know regarding the process is that an equivalent quantity of metal is substituted for the hydrogen." * Ee'ponse a M. Berzelius. Compt. rend., vi, 747. THE FARADAY LECTURE. 99 The chemists among my audience cannot but feel strongly the full importance, for the advancement of our beloved science, of this extensive series of re- searches on the constitution of organic acids, which, in the scantiest outlines, I have laid before them. Teeming, as they do, with a multiplicity of new facts, elucidating the nature of a large number of substances of widely diffused occurrence, and therefore of para- mount interest, they nevertheless claim our attention on still higher grounds. I have already alluded to the fact of their foreshadowing the doctrine of the non-equivalence of elementary atoms, now governing our notions in such a sweeping manner. But there is yet another direction in which these researches have exercised a powerful influence on modern ideas, If we compare the well-defined precision of our present conceptions of Molecule, Atom, and Equiva- lent with the vague and confused notions prevailing half a century ago, the salutary change must be looked upon as one of the most important features of the progress lately achieved. To this beneficial change the researches of Graham, Liebig, and Dumas on the poly basic acids paved the way ; and it is more especially to Liebig that we are indebted for the first unequivocal separation of the notions of equivalent and molecule ; for what he terms the atomic weight of an acid, in contradistinction to its equivalent, differs only in name from what we now call its molecule. This separation he advocated at all times, both in his writings and in his lectures, H 2 100 THE FARADAY LECTURE. but never more strenuously than when discussing the constitution of the polybasic acids, than which no class of compounds affords more striking illustrations of the difference between equivalent and molecule. The celebrated paper " On the Constitution of the Organic Acids," is by no means the only contribution which Liebig has made to our knowledge of this class of substances. Were I allowed to indulge in details, it would not be difficult to quote scores of acids, to the history of which he has supplied most valuable information. Let me only remind you that, in addition to the acids mentioned in the previous paragraphs, he studied formic, acetic, lactic, succinic, picric, and camphoric acids j he discovered fulminuric acid a fourth acid isomeric with the cyanic, fulminic, and cyanuric acids, which is formed by the action of chloride of potassium on fulminating mercury, and cyanurenic acid, a compound existing under certain conditions in the urine of the dog. In con- nection with his researches on alcohol and ether, he examined the salts of sulphovinic and phosphovinic acids ; and on the occasion of the memorable inquiry into the nature of fatty bodies, instituted under his auspices in the Giessen laboratory by Bromeis, H. Meyer, Playfair, Redtenbacher, and Varren- trapp, he published a series of most valuable papers on the stearic, margaric, and oleic acids. Nor must we leave unnoticed his joint investigation with Wohler of that singular organic acid, supplied in the form of its ammonium compound by the mineral THE FARADAY LECTURE. 101 kingdom. Liebig and Wohler's experiments estab- lished the simplest atomic formula of mellitic acid ; and it is but one more proof of the scrupulous accu- racy of the associated analysts, that this expression has been unequivocally confirmed by the splendid series of researches recently published by Baeyer, to whom it was reserved to assign to this remarkable compound, by converting it into benzol, its true position in the system of organic substances. I cannot conclude this rapid sketch of Liebig's more important experimental inquiries without allud- ing to the conspicuous results he obtained in the investigation of ALCOHOL AND ITS DERIVATIVES. I mention these researches last, not that I con- sider them of less interest than those which have preceded, but simply because, extending over a period of more than twenty years, they embrace some of his later as well as of his earlier discoveries. Liebig's first experiments on alcohol were made as early as 1832, when he examined its behaviour under the influence of chlorine. Everybody knows .that this inquiry, undertaken from purely scientific motives, led to the discovery of two compounds now in continual use for the diminution of human suffer- ing. Let us always thankfully remember that we are indebted to Liebig for the discovery of CHLORO- FORM, whose anaesthetic properties, now so admirably applied for the alleviation of pain in disease, enable even the severest operations of the surgeon's knife to 102 THE FARADAY LECTURE. be performed on patients lapped in complete uncon- sciousness, entirely exempt from the torture previously inseparable from such treatment. Nor must we ever forget that it was Liebig also who first presented us with CHLORAL, the benign properties of which for inducing sleep, when other soporifics fail, have rapidly established it in the highest rank amongst the thera- peutic agents placed by chemistry at the disposal of medical art. What an illustration of the practical advantages ever flowing from the pursuit of science, even when apparently most abstract ! Liebig, although he failed, at first, in establishing what are now considered the true formulae for chloral and chloroform, for which we are indebted to Dumas, described the method of preparing these substances, their properties and changes, with an accuracy which it would be difficult to surpass. It is to him that we owe hydrate of chloral, the beautiful crystalline com- pound now preferred for medicinal purposes. The formation of this hydrate presents a splendid phenom- enon of crystallisation, which I am tempted to exhibit to you. The flask before us contains a known quantity of the anhydrous liquid chloral, to which we now add an equivalent proportion of water. The two liquids are well mixed by agitation, when, as you observe, crystallisation immediately sets in, the walls of the flask becoming coated with a beautiful network of brilliant needles of the hydrate. It was Liebig who first observed the remarkable transformation of chloral into chloroform and formic acid by caustic THE FARADAY LECTURE. 103 alkali, which also we can easily illustrate by an expe- riment. For this purpose a small retort containing soda is provided with a condenser and dropping tube. On allowing a stream of chloral to flow in through the latter, you observe a powerful reaction, and on gently heating the retort, chloroform is volatilised, which collects as a heavy transparent oil at the bottom of the water in the receiver. The presence of formic acid in the residue is easily demonstrated by adding thereto a solution of corrosive sublimate and acidify- ing with chlorhydric acid, when a copious white pre- cipitate of calomel takes place. It was this easy transition of chloral into chloroform, which first sug- gested to Oscar Liebreich the happy idea of trying the physiological action of chloral ; as he expected that the small amount of alkali contained in the blood would be sufficient to produce this change, thus generating chloroform within the organism. Be this as it may, experiment has proved the physio- logical effect of chloral to be essentially different from that of chloroform, it being, in fact, rather hypnotic than anaesthetic, and possessing therefore a value of its own. It is certainly remarkable that two com- pounds, which for years presented an interest exclu- sively scientific, were found at last to be endowed with properties so eminently practical. In 1847, fully 15 years after its discovery, chloroform was used for the first time as an anaesthetic by James Simpson, and 20 years more had to elapse before the physiological action of chloral was discovered. 104 THE FARADAY LECTURE. Liebig's investigation of this substance, searching as it was, had not, probably on account of difficulties of production, been followed up, as it deserved, by chemists, whose laboratories throughout the world would hardly, in 1868, have supplied, collectively, so much as half a kilogramme of chloral. At the present date, only some seven years later, a factory in Berlin alone produces about 100 kilogrammes daily. In an assembly of chemists I need not dwell on the services rendered to science by chloral, since its abundant industrial production has made it available for day-by-day use in our laboratory researches. The object of Liebig's investigation of alcohol was to elucidate the constitution of this important compound and its derivatives. When he entered the field, Dumas and Boullay's celebrated memoir had already appeared. It is well known that the French chemists had been led to consider ether and alcohol as hydrates of olefiant gas ; Liebig, on the other hand, denied the existence of olefiant gas in these compounds, and regarded them as derivatives of a radicle, consisting of carbon and hydrogen, to which he gave the name of Ethyl. The long-protracted contest between the advocates of these rival theories forms one of the most interesting episodes in the early history of organic chemistry. It ended in a signal victory for Liebig, and a universal adoption of his theory. The olefiant gas, or, as it was also called, the etherine, theory, notwithstanding the new support which Berthelot's memorable transforma- THE FARADAY LECTURE. 105 tion of olefiant gas into alcohol at one time appeared to lend to it has well nigh fallen into oblivion ; whilst the theory which assumes ethyl to be a con- stituent of alcohol and ether is, at the present moment, as much in men's minds as it was when Liebig first suggested it, although our present view of the rela- tion between alcohol and ether has changed from that entertained by Liebig. Many of those here present will remember that, about a quarter of a century ago, Gerhardt and Laurent advanced their new system of chemical notation ; and while some of us witnessed, others perhaps shared, with somewhat of their youthful impetuosity, the contentions excited by the newly- proposed system. Let me remind you that the new ideas of the two French chemists were nowhere sooner countenanced than in this land of free debate ; and that, among the chemical warriors who took the field in their support, scarcely one was earlier afoot, and in his championship of the new system, no one more strenuous and successful, than the scientific chieftain under whose colours we are assembled this evening. Indeed, it is chiefly to Odling's efforts, courageously begun in early youth, and vigorously prosecuted in strong manhood, that England owes the honour of having been foremost of all nations to recognise the intrinsic truth and value of the new chemical doctrine. The modification, necessarily in- troduced by the new notation into the formulae employed by Liebig to express the composition of 106 THE FARADAY LECTURE. some of the substances which he examined, extends also to ether. When Gerhardt and Laurent's nota- tion is employed, Lie big's ether-formula must be doubled ; and this change (at the first glance at all events) appears but difficultly reconcilable with the views originally advanced by Liebig. Nor was it until Williamson, by experiments irresistibly con- vincing, elucidated the transformation of alcohol into ether, that this modification was generally accepted. Thanks to his masterly researches, we now, without a shade of doubt, look upon alcohol and ether as water in which the radicle ethyl has been substituted for one and for two atoms of hydrogen, or to use the more modern form of expression as ethyl united with the water-fragment hydroxyl, and ethyl linked to ethyl by the intervention of oxygen. I will not remind the members of a Society to which these classical researches were first presented that, far from invalidating Liebig's ethyl-theory, they have brought that hypothesis to its last and finest development ; but I will recall to memory the circumstance that to Liebig, Williamson owed the very agents he so successfully employed in the solution of this problem, viz., the ethylates of potassium and sodium. Strangely 'enough, Liebig never published a special paper on this subject, but only incidentally, in the course of his controversy with Dumas, mentions the formation, and describes the composition and properties, of these important compounds. When we think of the immense services these substances have rendered in THE FARADAY LECTURE. 107 the development of organic chemistry, it is but right that we should gratefully remember the chemist who supplied us with such powerful agents. I must not linger too long over Lie big's re- searches on alcohol and ether, but I cannot forego the pleasure of alluding to his deep-rooted conviction of the truth of his conceptions, as displayed by him in the course of some remarks on his attempt to de- compose ether with potassium. He says,* " I have no doubt that one day we shall succeed in isolating the radicle of ether, the hydrocarbon C 2 H 5 . Some experiments I have made upon the action of potas- sium on ether have failed to yield any decisive results. The metal becomes almost immediately coated with a film of oxide which prevents all further action ; but the investigation of the behaviour of potassium with the chloride or iodide of the radicle will soon show how far these conceptions are founded on fact." Were they founded on fact ? Which of us does not know that Lie big's dream, though many years later, was realised by Frankland, who, using the very reactions which floated in Liebig's mind, suc- ceeded in isolating the hydro -carbon radicle of alcohol and ether ? And here again, I hardly need remind the chem- ists in this assembly that the ethyl of Liebig's conception, and the ethyl we received from Frank- * Ueber die Constitution des Aethers und seiner VerUndungen. Ann. Chem. Pharm., ix, 15. 108 THE FARADAY LECTURE. land's hands, notwithstanding their identity of com- position, are two essentially different things. But I will remind them that nearly half a century has elapsed since Liebig endowed science with this fruitful conception. Compare the chemistry of that already remote period with the chemistry of the pres- ent day. On the foundations then scarcely visible above the ground, a palatial edifice has been raised, with pinnacles and dome, and busy labourers have added vast wings, not preconceived by the original architects ! Among the movements which the growth of chemistry evolved, there is, perhaps, not one more momentous in its consequences than the development, to which I have already alluded, of molecular in antithesis to atomistic conceptions ; and on no previous occasion, perhaps, did this an- tithesis more powerfully take hold of the mind of chemists than when Brodie, in a paper as remark- able for its brevity as for its sagacity, explained to the Chemical Society the difference between ethyl free and ethyl combined, between the molecule ethyl, C 2 H 5 .C 2 H 5 , and the fragment of that molecule, the group of atoms, C 2 H 5 , which, associated with other atomic groups, we assume in alcohol and its prolific progeny. And thus we may look upon it as a last, and by no means least remarkable outgrowth of Liebig's fertile mind, that his ethyl-theory, far from having, by the fact of isolated ethyl proving different from what he had anticipated, become ir- reconcilable with the evolution of modern ideas, has, THE FARADAY LECTURE. 109 on the contrary, supplied to chemists the most strik- ing examples for their elucidation. One more illustration, and we pass away from alcohol and ether. I remind you of an experiment which is familiar to every chemist in this room. The transparent liquid in this bottle, which rapidly sinks to the bottom of the test-glass filled with water into which we pour it, is oxalic ether. On addition of ammonia this ether solidifies to a beautiful crystalline mass, which you all know to be OXAMIDE. The fact of a crystalline body being produced by the action of ammonia on oxalic ether had long been known. Oxamide had also been obtained from ammonium oxalate ; but nobody suspected any connection be- tween these two reactions, until Lie big studied the process and taught us the simplest and most elegant method of preparing amides, a method now success- fully adopted in hundreds of other cases. It is impossible to speak of Liebig's labours on alcohol and on ammonia without alluding to the wonderful sagacity which enabled him by a ratiocina- tion, such as true genius only can evolve, to predict one of Wurtz's most beautiful discoveries. " It is of some interest," says Liebig, in an article on Organic Bases, * " to become acquainted with a view conceived for the purpose of explaining the properties of the nitrogenous organic bases. There is satisfactory proof that the oxygen of these bases has no share in their alkaline properties, every- * Handworterbuch der Chemie, i, 697. 110 THE FARADAY LECTURE. thing appears to indicate that these properties are dependent on their amount of nitrogen. " This view is based upon the chemical behaviour of ammonia, which may be regarded as the type of all organic bases, being the one which has the simplest composition. " The behaviour of ammonia with potassium, with mercuric chloride, and with certain organic acids, incontestably demonstrates that a portion of its hydrogen is replaceable by elements or compound bodies, playing the part of elements. Indeed, we know that potassium and sodium, when heated in ammonia gas, disengage therefrom 1 eq. of hydrogen, for which is substituted 1 eq. of potassium or sodium. These compounds, if amidogen be designated by the expression NH 2 = Ad, assume the following for- mulae : Hydramide (Ammonia). Potassamide. Sodamide. H + Ad K + Ad Na + Ad " Now we know that amidogen is capable of re- placing equivalent for equivalent the oxygen of many organic acids, and we find that the new compounds thus produced have altogether lost the nature of acids, being indifferent in their chemical character." " If the radicles of the oxalic and succinic acids which, when united with oxygen, give rise to acids, do, when in combination with amidogen, form bodies absolutely indifferent, the conclusion appears legiti- THE FARADAY LECTURE. Ill mate that amidogen by its union with compound radi- cles, which in their chemical activities stand nearer to itself, must generate substances, which, possessing the characters of ammonia, are organic bases." " If in the oxides of methyl and ethyl, the oxides of two basic radicles, we were able to substitute 1 eq. of amidogen for oxygen, there cannot be the slightest doubt that we should obtain compounds perfectly similar in their behaviour to ammonia. Expressed in a formula, a compound C 2 H 5 NH 2 = EAd, must have basic properties." Everybody knows that more than ten years later, the substances thus forecast by Liebig's penetrating intellect, were actually produced. Methylamine and ethyla.mine were discovered by Wurtz, and found to possess all the properties which Liebig's fertile imagination had assigned to them. I am almost afraid that this long enumeration of facts discovered or established by Liebig may have wearied you ; I will therefore, with your permission, from the mass of valuable and interesting subjects which must remain unmentioned, select only, and but for a moment's notice, Liebig's researches on the formation of acetic acid. - That alcoholic liquids, when exposed to atmos- pheric air, are, under certain conditions, converted into vinegar, had long been a familiar fact, but the exact nature of this process of oxidation remained 112 THE FARADAY LECTURE. without explanation. Nor had the question been advanced by the researches of Doebereiner, whose varied experiments served rather to obscure than to elucidate the subject. No sooner, however, had Lie big's perspicacious sagacity devoted itself to the inquiry, than the clouds, so long overhanging the process, were instantaneously dispelled. Liebig showed that the oxidation takes place in two suc- cessive phases ; the first consisting in the removal of hydrogen in the form of water, by which reaction aldehyde is produced ; the second, in the direct addition of oxygen to the aldehyde, which is thereby converted into acetic acid: and in his classical paper on the oxidation of alcohol, he has given an account of this typical process of transformation, so lucid and exhaustive, that but scanty gleanings have remained for his successors. The important inter- mediate compound which, even to the present day, we cah 1 the aldehyde par excellence, was introduced to us by Liebig, who, at the same time, discovered another compound closely aUied to aldehyde, and scarcely less interesting, viz., acetal. It is certainly worthy of remark that the same hand which gave us the first of aromatic aldehydes, also presented us with its prototype in the fatty series. In the whole range of organic chemistry, it would be difficult to name a compound more interesting and important than aldehyde. Endowed with an extraordinary power 'of combination, everybody knows that alde- hyde, when poured from one vessel into another, is THE FARADAY LECTURE. 113 converted into acetic acid exceedingly liable to intramolecular changes, when the opportunity of uniting with foreign matter is denied it capable lastly of processes of condensation which enable the chemist to pass, as it were, by bounds, from one series into another the aldehyde par excellence has, by this rare combination of properties, become an in- exhaustible source of discovery, from which even the chemists of the present day frequently and largely draw. This is not the place even to indicate the numerous researches of which aldehyde, at various times, and more especially of late, has been the sub- ject ; but I will at all events allude to the share of the harvest which has fallen to Liebig's lot. Met aldehyde, of which there is a specimen upon the lecture-table, such as few chemists probably have seen, was discovered by Liebig, who thus supplied an early and most striking illustration of poly merism. He also observed the still enigmatical power which aldehyde possesses of causing cyanogen to fix the elements of water, and to become rapidly converted into oxamide. Aldehyde was a favourite subject of Liebig's research, to which he returned on various occasions, either alone or in association with others. With Wohler, he examined the action of cyanic acid upon aldehyde, which gives rise to the forma- tion of that remarkable body, trigenic acid, the investigation of which deserves to be taken up again. Another splendid reward of their experiments was the discovery ofthialdine, a typical base containing 114 THE FARADAY LECTURE. nitrogen and sulphur, which is deposited in large well-formed crystals when sulphuretted hydrogen is passed into aldehyde -ammonia. Also carbothial- dine, the crystalline product of the action of bi- sulphide of carbon upon aldehyde-ammonia, which Liebig discovered and studied in conjunction with his friend and pupil Redtenbacher, deserves a passing notice. Nor should I, in conclusion, forget to mention that it was while studying aldehyde, that Liebig first observed the mirror-like deposition of silver from its solutions. The flask before me con- tains a slightly ammoniacal solution of silver. Let us have a last experiment. On pouring into this solution a few drops of aldehyde, and gently warming the liquid, the vessel, as you observe, instantaneously becomes coated with a lustrous film of silver, reflect- ing objects far more perfectly than a mercurial mirror. The process is marked with the simplicity which characterises so much of Liebig' s work. It forms the starting point of the manufacture of silver mirrors already spoken of in an earlier part of this lecture ; to the further development of which in- dustry Liebig largely contributed by his subsequent researches on the subject. I fear, Ladies and Gentlemen, that your atten- tion must be well nigh exhausted by the overwhelm- ing mass of matter I have had to compress into the narrow compass of this lecture ; and yet I feel how very imperfectly I have done justice to my subject, THE FARADAY LECTURE. 115 and how very meagre and fragmentary has been the outline of Liebig's voluminous life-work which I have been able to present to you. That an endless variety of miscellaneous observations ; that the long list of bodies the composition of which he determined whilst elaborating his method of organic analysis ; that the plant-ash analyses which, during his chemico- agricultural researches, were made either by himself or under his immediate guidance ; that the nume- rous elegant processes he gave for preparing sub- stances ; that his technical and domestic preparations his plan for making unfermented bread, for in- stance ; that the various methods with which he enriched mineral analysis ; that the several analytical processes which he supplied to physiologists and medical men ; that his analyses of nearly all the more important mineral waters of Germany : in one word, that his minor contributions to chemistry could not have found a place in this sketch, is self-evident. But any one who has made himself acquainted with the glorious career of Liebig must be aware that whole branches of his far-reaching activity have been altogether left unnoticed. I have scarcely alluded to his searching and frequently resumed inquiry into the nature of the organic alkaloids, a field of research, on which he occasionally broke a lance with Hegnault, then working on the same subject ; but I may remind you that many of the formulae of the alkaloids now-a-days adopted, are based on Liebig's determinations. Nor has that I 2 116 THE FARADAY LECTURE. remarkable series of chemico -physical experiments been mentioned, which suggested themselves to Liebig, whilst he was engaged with his researches in animal chemistry. The results of these experi- ments relating to diffusion, to endosmosis, and exos- mosis, and to like phenomena playing an important part in the motion of the juices of the animal or- ganism, are published in a separate pamphlet.* Again, I have not even noticed a field of inquiry which Liebig cultivated with never-ceasing predi- lection, since so many of his researches on collateral subjects very naturally converged thereto. I am speaking of his study of those grand processes of transformation, by which matter circulating in the animal and vegetal kingdoms, is continually return- ing to the world's mineral stores. On more than one occasion he developed the peculiar views he had formed of fermentation, putrefaction and decay, a subject to which was devoted even the last paper he ever wrote, an elaborate memoir on fermenta- tion, and on the source of muscular power. We cannot indeed flatter ourselves with having yet arrived at the final solution of these great ques- tions ; and it will suffice here to remind you that Liebig was a staunch opponent of those by whom * In Germany the pamphlet appeared under the title : Ueber einige Ursachen der Sdftebewegung im thierischen Organismus. Braunschweig. The English edition bears the title: Researches on the Motion of the Juices in the Animal Body. By Justus Liebig, M.D. Edited from the manuscript of the author by William Gregory, M.D. London, 1848. THE FARADAY LECTURE. 117 the lower forms of vegetal and animal life are con- sidered to be the cause of these processes, and whom he facetiously compared to the man who imagined the Rhine to be driven by the row of watermills which he saw across the river near Mayence. And to mention yet one more field of Liebig's life-long labours, which, did time permit, it would be most interesting to survey, let me remind you of his long- continued activity as an experimental critic. The brief sketch, which, in a previous part of this lecture, I have endeavoured to give you of his contest with Gerhardt and Laurent, may have served to impress you with his controversial style ; but it does not convey to you the remotest idea of the influence which he exercised by reviewing the researches of others, by submitting them, regardless of anything except the interest of truth, to the crucial test of experiment, sometimes confirming, sometimes refuting them, but at all times throwing new and unexpected light upon the subjects under discussion. In the preceding sketch, devoted more especially to Liebig's experimental labours, I have naturally omitted to allude to his purely literary achievements. Of an essentially different kind, this work is not less comprehensive, and scarcely less influential. Every chemist knows the celebrated periodical, " The Annalen," founded by Liebig in early life (1832), and which in later years, for a very considerable period, he published in conjunction with his friends 118 THE FARADAY LECTURE. Friedrich Wohler and Hermann Kopp. Of this invaluable collection, no less than 165 volumes had appeared at the time of Liebig's death ; and there is no journal which more faithfully and more thoroughly represents the progress of chemical dis- covery during the last half century. For generations of chemists it has been an object of ambition to become contributors to its volumes : they contain all the researches performed subsequently to 1832, either by Liebig himself, or by the pupils of the Giessen school. The present editors have, therefore, both gratefully and wisely decided to retain the auspicious appellation, " LIEBIG'S ANNALEN" on the title-page of the journal. Another grand literary work, undertaken jointly with his friends Poggendorff and Wohler, was the publication of the " Dictionary of Pure and Applied Chemistry," * the first parts of which appeared in 1836, and which, after many interruptions, was completed in 1856. For years this work has been one of the principal sources of chemical information. The new dictionary of chemistry which, under the auspices of Prof, von Fehling, has just been started by the celebrated German publishers, Friedrich Vieweg and Son in Brunswick, is founded on the work of Liebig. * Handwdrt&rbuch der reinen und angewandten Chemie. in Ver- bindung mit mehreren Gelehrten herausgegeben von Dr. J. Liebig, 7)r. J. C. Poggendorff, und Dr. Fr. Wohler. Braunschweig, bei Vieweg und Sohn. THE FARADAY LECTURE. 119 Following closely upon the first volume of the Dictionary appeared the " Handbook of Organic Chemistry." The origin of this book was a peculiar one. Philipp Lorenz Geiger, the author of a once celebrated work on Pharmacy, and one of Lie- big's early scientific friends, had died in 1836. In the interest of the widow, Liebig generously under- took to revise the chemical part of Geiger's Phar- macy, when a new addition was wanted. But the strides which chemistry had made in the compara- tively short time since the last edition had appeared, were such that Liebig very soon gave up the idea of simply improving the work of his late friend. He began to re-write the book, and indeed the volume on Organic Chemistry is entirely an original work.* Now that more than thirty years have elapsed since its publication thirty years of wondrously active progress in organic chemistry we cannot but admit that what had previously been a mass of incoherent knowledge, assumes in Lie big's work, for the first time, the form of a finely articulated science. For thousands, not only in Germany, but in all other countries, has it been the leading thread of Ariadne. Immediately after its appearance, a French transla- tion of it was published by Gerhardt; into English it was translated by Gregory, and published as the * Handbuch der Chemie mit Rucksiclit auf Pharmacie, von Dr. Justus Liebig (als neue Bearbeitung des ersten Bandes von Geiger's Handbuch der Pharmacie). Heidelberg, bei Winter. 1843. 120 THE FARADAY LECTURE. part on organic chemistry of the later editions of Turner's celebrated work. The death of Berzelius, in 1848, involved Lie big in another literary undertaking of consider- able magnitude. One of the means by which the illustrious Swede had exerted his powerful influence had been by his Annual Report on the progress of Chemical Science. For many years, translated into German by Wohler, these annual reports had become, for all investigators, a kind of central source of information, the publication of which was eagerly looked forward to. When Berzelius died, public opinion among chemists, with rare unanimity, desig- nated Liebig as the one to continue the work. It was not without hesitation that he accepted the task ; the difficulties of which, from the ever-increasing expansion of the field of inquiry, he clearly foresaw were to augment with every year. Nor did he con- sent single-handed to take the field. It was not until he had secured the co-operation of his friend Hermann Kopp, the author of the classical History of Chemistry, then Professor of Chemical Physics in the University of Giessen, that the new Report was started. And since the work was by no means to be devoted exclusively to chemistry proper in its several ramifications, but was to embrace also the progress of the collateral sciences, physics, mineralogy, geology, and technology, the two editors induced several other teachers in the University of Giessen H. Buff, the physicist, E. Dieffenbach, the geolo- THE FARADAY LECTURE. 121 gist, C. Ettling, the chemist and mineralogist, F. Knapp, the technologist, H. Will, the chemist, and F. Zamminer, the physicist to join their labours, and thus, viribus unitis, was inaugurated in 1849 that magnificent series of Reports/* which, although the editors have changed more than once,t has continued for upwards of a quarter of a century to supply a record of chemical discovery, such as no other language can boast of. With the observa- tions of a legion of investigators, scattered through a hundred journals, in five or six languages, half the time of the inquirer would, but for a work like this series of Reports, be lost in searching all literature for the information extant on the subject of his investigation. Indeed, every experimenter must feel the debt of gratitude which, for help received even before the commencement of his labours, he thus owes to Lie big. Of Liebig's great works on agricultural and phy- siological chemistry embodying, as they do, his most important experimental inquiries, I have already had to speak ; but I must not conclude this enumeration of his literary achievements, without alluding to one of his noblest productions, from which, more than * The German title is : Jahresbericht uber die Fortschritte der reinen, pharmaceutischen und technischen Chemie, Physik, Mineral- ogie und Geologie. Giessen, J. Ricker'sche Buchhandlung. f The reports were published from 1847 to 1856 by Lie big and II. Kopp; from 1857 to 1862, by H. Kopp and H. Will; from 1863 to 1866, by H. Will alone; during 1867 and 1868, by A. Strecker; and since that time by A. Naumann. 122 THE FARADAY LECTURE. once in the course of this lecture, I have had an opportunity of quoting. I mean his " Familiar Letters on Chemistry."""* They are a charming illustration of a truly popular work on Chemistry. The book is translated into all modern languages. The English edition, Liebig dedicated to the late Sir James Clark, for whom he, like so many others, entertained the highest esteem and the warmest friendship. Few works of a similar character have had a circulation, and exercised an influence, like these familiar letters, from which accurate chemical notions and a sound appreciation of natural phenomena have penetrated into all classes of society. To the student of Liebig's works, these letters present a double interest, im- pressing him, as they do, with the seductive elegance of his language, the lucidity of his composition, and the cogent power of his reasoning, and affording him, at the same time, an opportunity of surveying at a glance, as it were, the whole field over which Liebig's active mind has ranged. In these letters, which for ' the most part first appeared in the well-known South German newspaper, the " Augsburger Allgemeine Zeitung," Liebig used to give from time to time the results of such of his experimental enquiries or * The German title of the book is Chemische Brief e. In Eng- land it appeared under the title : Familiar Letters on Chemistry, in its relations to Physiology, Dietetics, Agriculture, Commerce, and Political Economy, by Justus von Liebig. London: Taylor and Walton. The letters were first admirably translated by Dr. John Gardner. Later editions are by Prof. W. Gregory; and the last one (fourth) is by Prof. John Blyth. THE FARADAY LECTURE. 123 philosophic meditations as could be rendered acces- sible to the general reader ; and thus we find him treating in them all the various subjects which in succession engrossed his attention ; they contain essays on the philosophy of chemistry, on experi- mental science, on the results of his chemical inves- tigations in agriculture and animal physiology, on industrial chemistry, &c., in a word, on all topics of philosophical interest, which casual circumstances, such as the perusal of an interesting book, an animated conversation, a stirring event of life, might happen to suggest. Thus the admirable letter"'" on the spontane- ous combustion of the animal body, exploding for ever the notions floating in the heads of medical men and lawyers but a comparatively short time ago, was occasioned by a cause celebre, the murder of the Countess of Gorlitz in Darmstadt, by her servant man, at whose trial Liebig appeared as a scientific witness for the prosecution, and whose conviction was essentially promoted by the irresistible scientific evidence that he adduced. The letters were first published in a collected form in 1844 ; since which time the work has gone through many enlarged and revised editions. To complete the list of Liebig's publications, it is necessary to refer to a large number of contro- versial pamphlets, chiefly on agricultural subjects ; * Letter XXII of the third edition. In Germany the letter is separately reprinted under the title, Zur Beurtheilung der Selbst- verbrennung des menschlichen Korpers. Heidelberg, 1850. 124 THE FARADAY LECTURE. to a variety of popular lectures ; and to a long series of essays and of academical discourses which, in his capacity of President, he addressed to the Bavarian Academy. Amongst the polemical papers, his long controversy with J. B. Lawes and J. H. Gilbert is best known in this country, on account of the eminent position of his opponents among English agricultural chemists. Liebig has defended his views on the question at issue in a special pamphlet.'"" Among his essays, two very important papers, " On the state of chemistry in Austria " (1838), and " On the study of the natural sciences, and on the state of chemistry in Prussia " (1840), must be singled out ; since they have exercised a most powerful influence on the de- velopment of chemical education in those two countries the Governments of which they impressed with the necessity of providing ample funds for the foundation and endowment of institutions for instruction in ex- perimental science. Lastly, among his academical speeches, as having particular interest for English readers, his discourse " Francis Bacon of Verulam, and the History of the Natural Sciences " may be specially quoted. These essays, lectures, and dis- courses, together with various papers on subjects of general interest, were collected by Liebig's son-in- * Die Grundsatze der Agriculturchemie mit Hucksicht auf die in England angestellten Untersuchtingen. Braunschweig, 1855. The English edition bears the title: Principles of Agricultural Chemistry, with special reference to the late Researches made in England. By Justus von Liebig. London, 1856. THE FARADAY LECTURE. 125 law, Professor M. Carrier e, of Munich, who in 1874 published them in a separate volume."* I cannot presume to suppose that in these cursory sketches of Lie big's scientific, and more especially of his experimental labours, I have conveyed to the chemical part of my audience any fact not known to them before. We were none of us less familiar with our combustion tube than with our balance, with our five-bulb apparatus than with our thermometer. The substances of Lie big's discovery, that we have passed in review, are among those which are of most frequent use in the laboratory. The course which the chemical student follows in performing his mine- ral analysis is Liebig's. The reactions he taught us are those most commonly employed in our researches. His works on agricultural and animal chemistry are in everybody's hands. His " Familiar Letters on Chemistry," who has not read ? You will charge me, I fear, with teaching grown-up men the first letters of their alphabet. I do not deny the imputation. The fault, if it be one, so far from weakening, does much to strengthen my case. We could not more eloquently bear witness to the influence Justus von Liebig has exercised upon the progress of our cherished science, than by frankly acknowledging that his teachings have become familiar to us as "household words." * Eeden und Abhandlungen, von Justus Liebig. Leipzig 11. Heidelberg, 1874. 126 THE FARADAY LECTURE. Thus far, Ladies and Gentlemen, I have endea- voured to sketch to you Liebig the philosopher, the chemist ; can I part from you without alluding to Liebig the man ? Had I the power of delineating to you his character as it lives in my grateful memory, you would agree with me that our respect and admira- tion are by no means exclusively due to him for his scientific achievements. Among the many noble lessons that his great life teaches, we may learn that a generous heart, perpetually solicitous for the good of mankind, is as necessary to the true philosopher (in the highest sense of that comprehensive term) as a penetrating intellect ; and that our anxiety to discover abstract laws should never be dissociated, in our hearts and minds, from an anxiety, as searching and intense, to find for these grand laws special applications conducive to the well-being of our race. The leading feature of Liebig's character is his incorruptible love of truth, repudiating untruth, even in jest ; indeed, he well deserves the praise which Cornelius Nepos bestowed upon Epaminondas adeo veritatis diligens ut ne joco quidem mentiretur. This veracity is strikingly manifested by the readi- ness with which he gives up the opinions he at one time believed to be correct, but subsequently recog- nises to be erroneous. And it is without reluctance that he thus abandons ideas once cherished and even vigorously advocated ; for to persist in views no longer tenable, simply because he once conceived THE FARADAY LECTURE. 127 them, appears to him a melancholy proof of incapacity for progress. He admits with perfect candour any errors into which he may have fallen ; " there is no harm in a man's committing mistakes," he used to say, " but great harm, indeed, in his committing none, for he is sure not to have worked." And characteristic is the eagerness, I had almost said anxiety, with which he endeavours to correct mistakes once recog- nised. " An error you have become cognisant of," he once said to me, " do not keep in your house from night till morning." It would be strange if a man of such disposition should have borne ill-will to those who pointed out or corrected his mistakes. On the contrary, it was a noble endowment of Lie big's generous nature that he welcomed, in the interest of truth, what to most men would have appeared an annoyance. Let me give you a case or two in point. I mentioned in a former part of this Lecture that the expressions originally adopted by Liebig for chloral and chloroform were erroneous : and that we are indebted to Dumas for the formulae of these important compounds, which are now generally ad- mitted. How does their discoverer receive this emendation of his results ? Listen to what he says himself on the subject, when, at a later period, in a scientific dispute with another, he wishes to impress his anta- gonist with his views regarding experimental con- troversy. " As an excellent illustration of the mode 128 THE FARADAY LECTURE. in which errors should be corrected," Lie big* says, " the investigation of chloral by Dumas may fitly be adduced. It carried conviction to myself and, I think, to everybody else, not by the copious number of analytical data opposed to the not less numerous results which I had published, but because these data gave a simpler explanation, both of the formation and of the changes of the substances in question. To analytical data alone, no one and Dumas least of all would have attached the slightest import- ance." Even more striking, perhaps, because of the much more important question at issue, is the example of ready submission to correction, which he gave in the early stages of his agricultural inquiries. It is well known that his first mineral manure, which was manufactured, in 1845, according to indications he considered as the practical embodiment of his theo- retical researches, and which was to present to the farmer " the elements of the ashes of the plants to be grown," proved an utter failure. The cause why he failed has long become obvious. Lie big, fearing that the soluble alkaline constituents of his manure might be washed away by the rain-water percolating through the soil, had endeavoured to render these constituents less soluble, by submitting his fertilizing compound to incipient fusion in a reverberatory furnace. This fear, very legitimate according to the * Bemerkungen zu dem Aufsatze tiber die Constitution der Zucker- sdure, von H. Hess. Ann. Chem. Pharm., xxx, 120. THE FARADAY LECTURE. 129 knowledge of the time, was soon recognised to be without foundation. Only a few years later (from 1850 to 1855), John Thomas Way discovered the absorptive power of soils, which enables them to withdraw the plant-food from its aqueous solution, as it percolates the earth. Liebigat once perceived and acknowledged the immense importance of this discovery, although it required him to modify, in some of its essential features, the theory of plant- nutrition he had originally advocated. He confirmed and amplified, by numerous experiments of his own, Way's observation, which, indeed, acquired its full development only after Lie big had pointed out the grand part which the absorptive power of soils has to play in the economy of nature. If, notwithstanding this marked readiness to accept correction whencesoever it might come, we find Liebig almost continually engaged in scientific warfare, the source of this warfare is, after all, the same love of truth. Any opinion he considers to be true, he will support and defend with an ardour little short of passion ; and woe to adversaries who should avail themselves of disingenuous artifices, or irritate him by unjustifiable subterfuges ; he will flame up in sudden zeal, and who would deny it ? occa- sionally overshoot his mark ; but then, even in the next moment, his better j udgment returns, and, bent on reconciliation, he is ready to bring the contest to an amicable conclusion. And, the dispute once settled, all angry feeling, which the excitement of K 130 THE FARADAY LECTURE. the strife might for a moment have created, seems utterly sunk into oblivion. Indeed I shall never forget the glowing delight with which Gerhardt described to me the friendly reception he met with at Liebig's hands, when, some time after the fierce collision to which I have referred, he visited him at Munich. And here, perhaps, I may also fitly recall the noble sentiments which Liebig uttered when, immediately after our late war with France, at a time when the waves of irritation were still running high, he addressed the Bavarian Academy. Although, of all German chemists, the one who had been most frequently in dispute with our French colleagues, he was, nevertheless, the first to hold out the hand of reconciliation, the readiest to soothe the hostile feel- ings of the moment by an appeal to the glorious traditions of the past. " This is, perhaps, a fit opportunity," says Liebig,* " of declaring, on the part of our Academy, that a hatred of race (Stammeshass) between the German and the Latin nations does not exist. " We look on the heavy affliction which in former times the French nation has caused to Germany as on an illness, the pains of which are utterly forgotten with the return of health. " The peculiar nature of the German, his know- ledge of languages, his appreciation of other nationali- ties, compel him to do justice to foreigners, so much * At the meeting of March 28, 1871. JReden und Abhandlungen, p. 333. THE FARADAY LECTURE. 131 so as occasionally to become unjust to himself; and thus we cannot possibly underrate the debt of grati- tude we owe to the great philosophers, mathema- ticians, and natural inquirers of France, who, in so many departments, have been our masters and exem- plars. " When, 48 years ago, I went to Paris for the purpose of studying chemistry, I was fortunate enough to gain, by an accidental circumstance, the attention of Alexander von Humboldt, whose recommendation induced Gay-Lussac, one of the greatest chemists and physicists of his time, to honour me, the youth of twenty, by the proposal of con- tinuing and completing with his co-operation an inquiry I had already commenced. He received me into his private laboratory as a pupil and fellow- worker, an event which has shaped the course of my life. " Never, indeed, shall I forget the kindness which the German student met with at the hands of Arago, Dulong, and Thenard ; and how many of my German countrymen, medical men, physicists, and orientalists could I name, who, like myself, remember with gratitude the active support in the attainment of their scientific aims, which was liberally accorded to them by the French savants. " Warm sympathy for all that is noble and great, and disinterested hospitality, are among the finest features of the French character. It will be on the neutral ground of science that the best minds of the K 2 132 THE FARADAY LECTURE. two nations must meet in endeavouring to reach the high goal common to both, that these sentiments will be kindled again into life and activity ; and thus the feeling of fraternity in science, which can never be entirely extinguished, will gradually contribute to mitigate the bitterness with which the deeply- wounded national pride of the French is filled by the consequences of the war they have forced upon us." In speaking of Liebig's character, it is delightful to remember the absence of anything like personal vanity. Few scientific men, probably, have been equally loaded I might almost say overwhelmed with honours. Scarcely an academy or learned society that did not consider it an honourable duty to elect him a member long before he had reached middle life. The highest scientific distinctions which England, France, and Germany can bestow, the Copley medal, the Foreign Associateship of the French Institute, the order pour le merite, were in his possession. Thankfully as he had accepted these honours, they had so little changed the simplicity of his character that many of his intimate friends were ignorant of his having received them. His feelings as to such outward tokens of approbation are well expressed iu a letter addressed to his friend, Thomas Graham, on the occasion of his receiving from this country a gift of honour, which he highly appreciated. When, in 1852, Liebig left his professorship in Giessen for the purpose of accepting an academical position in Munich, his friends in England associated, THE FARADAY LECTURE. 133 \ under the auspices of Thomas Graham, in order to present him with a mark of recognition. The correspondence between Graham and Lie- big, to which the presentation of this testimonial gave rise, deserves for more than one reason to be remembered, since it reflects honour on both men. In his capacity as Chairman of the General Com- mittee, Graham accompanied the transmission of the testimonial with the following letter : " SIR, London, July, 1854. " Your retirement from the Chair of Chemistry, in the Uni- versity of Giessen, has appeared to many in this country a fit- ting occasion for the public acknowledgment of your eminent scientific services. Accordingly a numerous body of your friends and admirers have united to present to you a Testimonial, coiu- memorative of their profound and unalterable regard. In the list of subscribers hereto annexed, you will recognise, with those of your pupils and personal friends, the names of many other gentlemen eminent in science, in social position, and in the prac- tical arts of life, who were anxious to join in this just tribute to your merit. " In presenting to you this Testimonial, the subscribers desire to express their sense of the benefits which your genius and labours have conferred upon mankind, in adding to the world's stock of positive knowledge. These benefits are limited to no one people or time ; but it is felt that Englishmen may, with propriety, take the lead upon this occasion, as the impulse which you have given to Chemical Science has been experienced especially in England. More students from this country than from any other land beyond the bounds of Germany, have worked in the Laboratory of Giessen, and have derived incalculable bene- fit from the instruction there imparted, and from the noble ex- ample there presented to them of an elevated philosophical and scientific life. In England, also, have the applications which you have made of Chemical Science to the cultivation of the soil 134 THE FARADAY LECTURE. been peculiarly appreciated and adopted. Your discoveries in practical agriculture have enriched the land, and with you origi- nated the method of scientific inquiry which is here pursued on an extended scale by numerous investigators, and which is rapidly changing the features of the most ancient and important of human arts. " We earnestly hope that your life, which has been devoted to the highest aims to which man can aspire, may be prolonged to many years of happiness and honour. " Signed on behalf of the subscribers, "THOMAS GRAHAM, " Chairman of the General Committee. "To Baron Liebig." Liebig replied : " SIR, " Munich, July 20, 1854. " The man of Science generally knows of no other reward for the time he has devoted to the discovery of truth and to the investigation of the laws of Nature's powers, than the mental satis- faction which springs from the consciousness of having, to the best of his ability contributed his part towards the advancement of human happiness and human welfare ; for toils like his, attended as they are with so many difficulties and sacrifices, and with such mental effort and fatigue, cannot be priced in the market or sold, cannot be performed to order, or turned into money. If he has been fortunate enough to have gained by his successes the acknowledgment and esteem of his contemporaries, he has obtained the highest object of his ambition. " If I have laboured for the period of almost a human life, in promoting the progress of Chemistry, and in making its prin- ciples subservient and useful to other branches of knowledge, more especially to the industrial Arts and to Agriculture, I gratefully acknowledge that I have received in return all that a man could justly aim at. My satisfaction in this respect is not a little enhanced, when I look back to the number of zealous and able men in whose education I have been enabled to assist, and who are now occupying, in various countries, a distinguished position in the front rank of science, and are, with splendid THE FARADAY LECTURE. 135 success, cultivating and extending her domain, teaching, dif- fusing, and successfully applying those principles of investiga- tion which constitute the true foundations of scientific progress. It is with pride that I am able to add that, in these, my former pupils, I have gained an equal number of warm friends, who, I am sure, look back with pleasure to the time when we combined our powers in one common aim and effort. "And now, in addition to all that a benevolent destiny had already granted me in measure above many, I receive from my friends in England, in this gift of friendship, in this testimonial of honour, a token and a proof of their recognition and appro- bation of my labours. " When I reflect that whatever of good a man accomplishes, flows from an inner impulse of which he is often but imperfectly conscious, and that a higher power has a part in all his labours of usefulness, giving to them their life-germ and their capa- city of growth, I must own that, in receiving this noble Present, I am blessed far beyond my deserts. " I feel myself in the highest degree honoured and most deeply touched by this substantial and permanent expression of the kind feelings of my friends in England. Convey to them all my best and warmest thanks. This Gift of Honour possesses for me inestimable value, and will remain a lasting memorial in my family. "Dn. JUSTUS VON LIEBIG. " To Thomas Graham, Esq., " Chairman of the General Committee" One of the last paragraphs of Liebig's letter is particularly interesting, touching, as it does, on sub- jects regarding which the views of so profound a thinker can be indifferent to no one. It is only from passages scattered throughout his writings, that it is possible to infer the position held by Liebig towards the grand enigmas, the solution of which, vainly aimed at by generations past, will equally 136 THE FARADAY LECTURE. baffle the curiosity of generations to come. But rarely did Liebig unfold the ideas he had formed of God and immortality. With regard to the latter, more especially, he seemed to hold the opinion of Goethe, who thought that the best mode of pre- paring for the life to come was to do well the business of this.* The concluding passage of his letter to Graham, however, shows distinctly how deeply he was convinced of a supreme power regulating the affairs of this world. More at length, though perhaps not more expli- citly, he has expressed his views in his Familiar Letters on Chemistry : " Were a chemist to submit a house to analysis, he would state its composition scientifically to consist of silicium, oxygen, aluminium, calcium and of a certain quantity of iron, lead, copper, carbon, and the elements of water. But this would not convey the most distant idea of the construction of a house. The calcium, carbon, and oxygen of the mortar ; the silicium, aluminium, and oxygen of the bricks ; the carbon, hydrogen, and oxygen of the wood, do not play the part of elements in the structure, but they are present in the form of mortar and stone in the walls, as glass in the windows, as woe +he tables and seats. It is only when combined in the form of wood, stone, glass, &c., that these elements contribute to the construction of the house. * Eckermann, Gesprache mit Goethe in den letzten Jahren seines Lebens, I, 122. THE FARADAY LECTURE. 137 " If any one assured us that the palace of the king, with its entire internal arrangement of statues and pictures, started into existence by an accidental effort of a natural force, which caused the elements to group themselves into the form of a house, because the mortar of the building is a chemical compound of carbonic acid and lime, which any novice in chemistry can prepare, because the stones and glass consist of silicium, aluminium, calcium, potas- sium, and oxygen, united by chemical affinity, and indebted to the force of cohesion for their solidity, because, therefore, chemical and physical forces play a part in the construction of the house, we should meet such an assertion with a smile of contempt, for we know how a house is made. Its outer form, its inner arrangement of rooms, &c., proceed from the architect. He constructs the actual house after the plan of an ideal house which exists in his own mind, He realises the ideal creation of his own mind in the building by forces which are produced in the organism of man, and which impress into the service of this ideal creation the chemical and physical forces from which the building material has received its proper- ties. E Tr ere the existence of a house presup- poses the ideal perception of the house in the mind of some one who is its builder or cause, which sets other forces in action in certain directions, or in a certain form, in order to gain the object in view.""' * Familiar Letters on Chemistry, 4th edit., 285. 138 THE FARADAY LECTURE. In the preceding sketch I have given you some glimpses of Liebig's character, so far as it is reflected in his writings and in his demeanour towards scien- tific contemporaries. I need scarcely add that the same nobility of thought and generosity of feeling which mark the various stages of his scientific career are also manifested how could it have been other- wise 1 in all the relations of every-day life. Every word, every gesture, was the expression of affability and kindness, although a measured dignity would keep at a distance the profane. In his intercourse with intimate friends he displayed a cordial simplicity irresistibly captivating ; towards his pupils notwith- standing the dignified composure of his deportment an affectionate kindness, encouraging even the most timid beginner, and assuming towards the assiduous worker the form of a helpful sympathy which shrunk from no sacrifice, and lasted far beyond the period of personal intercourse. Nor is it only by friends and pupils, or by those whom he was wont to meet in society or in the trans- actions of ordinary life, that the countless manifes- tations of genuine interest, of ever-ready counsel, of active support, are thankfully remembered. It was impossible to come even into casual contact with him without being deeply impressed by the generous dis- position which prompted him to help where help was wanting, alike whether the seeker was a friend or stranger. Although Time's creeping hand upon the dial THE FARADAY LECTURE. 139 warns me not to venture into detail, I bear in memory a little incident so charmingly illustrative of Liebig's genuine goodness of heart, that I am tempted, if your permission be given, to relate to you this cha- racteristic anecdote. Many years ago (in 1853), Liebig was making an excursion among the mountains of the Tyrol ; and I and two others of his friends had the happiness of being his companions on the tour. In the course of our rambles one morning we overtook an old soldier who was travelling slowly along the road, much wasted by fatigue and obviously enfeebled by disease. As we came up with him he accosted us with a piteous tale, and humbly implored our aid. Following Liebig's example, whose purse on such occasions was ever as freely open as his heart, we made up among us a little stock of florins, which the poor man evidently regarded as a small fortune dropped by Providence into his hand ; then pushing forward, we soon left him behind, and in half-an-hour's time reached a village inn at which we agreed to rest ourselves and dine. While thus engaged, we observed our poor way- farer also enter the inn. It pleased us to reflect that, for this once, at all events, he had the means of pro- curing a comfortable meal ; and, having finished our own, we resolved to take a short siesta before setting out again on our journey. After some half-an-hour's doze, I awoke and found two of my companions fast asleep in their chairs, whilst Liebig, to my surprise, 140 THE FARADAY LECTURE. had disappeared. I immediately got up, and, pro- ceeding to the bar, inquired of the innkeeper where our friend, the elderly spare man of our party, had gone. The landlord replied that the gentleman had been inquiring, a little while ago, for a pharmacy ; and that, upon learning that there was none in the village, nor any nearer than in the next village over the hill, he had set out on foot in that direction. Not without some little anxiety at the temporary dispersion of our party, I at once proceeded on the road which Liebig had taken. After half-an-hour's walk, I observed his figure on the brow of the hill, and hurried forward to meet him, impatient to learn the object of his solitary promenade. He answered me simply, that he had perceived in our poor soldier symptoms of low fever, such as quinine was certain to cure, and that he had been over to the nearest pharmacy to get some of this remedy. On his arrival, he added, the apothecary chanced to be absent ; but his wife had given him (Liebig) the free run of the bottles, with permission to select therefrom any article he might desire, paying, at his own price, for whatever he might take. He went on to tell me that, fortunately, he had discovered the quinine- bottle, and made up, with a portion of its contents, a boxfull of powders, sufficient, he hoped, for our wanderer's perfect cure. After another half-hour's walk, the powders were delivered to the soldier, with instructions how often they were to be taken. Not a word was said of the long walk they had cost the THE FAHADAY LECTURE. 141 kindly donor. After receiving the poor man.'s ex- pressions of gratitude, and promise to obey the in- structions given him, we immediately resumed our journey, and I observed, that though Lie big had been toiling over the bilk while we slept, he was not, during the remainder of our walk, the least cheerful and buoyant of the party. This is but one of many touching pictures I could give of this great man's noble simplicity of character and genuine self-sacrificing kindliness. We lads had given the poor sufferer our coin a-piece, and then had gone to sleep, considering our duty done. The master had noted the wayfarer's illness, and resolved on striking at the root of his distress ; to which humane end he had generously sacrificed his own much-needed hour of repose. Is it to be wondered at if we, his former pupils and ever-devoted friends, in admiring the chemist also loved the man ? And here, Ladies and Gentlemen, I may fitly bring my discourse to a conclusion by again pro- nouncing the great name which, in accordance with the nature and occasion of this lecture, I have had, on its very threshold, to invoke. In this theatre, hallowed as it is by the memory of Faraday's genial presence, how could I speak of Liebig's generous character, of his benevolence, of his kindliness, of his simplicity of life, without reminding you in how high a degree these eminent moral qualities adorned also 142 THE FARADAY LECTURE. the character of Faraday? In contemplating the life-long work and conduct of these two great con- temporaries, our admiration for both is at first natur- ally called forth by the marvellous capacities of their commanding intellects, soaring, each in its special sphere, far beyond contemporary effort, and resem- bling one another in the extent of their penetrating and inventive power. Pursuing the comparison, we are finally struck with the profound resemblance of the two great discoverers in all the highest, purest, and most beneficent qualities which can adorn and dignify the human heart in their never leaving un- assuaged any form of human want or suffering it was within their power to relieve, and never, even in the zenith of their world-wide celebrity, wearing their high honours with undue pride, but being always ready, with child-like kindness and simplicity, to welcome and enlighten the youngest and humblest inquirer in the mysteries of philosophic truth. Of Faraday's generous disposition in this respect, I am favoured by the kindness of Mr. F. O. Ward, with the means of laying before you a touching ex- ample. My friend, anxious as he expresses himself, to contribute a little mite of his own towards our affec- tionate commemoration of Faraday's goodness of heart, has handed me an autograph letter dated June 16, 1834, and addressed by Faraday to him, then a lad in his teens, studying science at King's College, London. This lad, like many others of THE FARADAY LECTURE, 143 his age, had indulged in a day-dream about the nature of matter, the shape of atoms, and the pro- bable relation of their form to their respective chem- ical properties. With boyish pride (I am quoting my friend's own recital of the anecdote), the budding philosopher is eager to submit this visionary intel- lectual ramble to the greatest scientific authority of the age, and probably not less confident than soli- citous of obtaining the master's approval for this, his first young venture on the darksome sea of the un- known. Accordingly, with the audacity belonging to his period of life, though wholly a stranger to Faraday, and not even supplied with a letter of introduction to him, he forwards to this Institution, then Faraday's home, the statement of his wander- ings in philosophic dream-land, with a request for Faraday's opinion of the theory propounded, and his advice, whether it would be worth the writer's while to test its value by experiment. Nine men of genius out of ten, my friend very truly remarks, in the matu- rity of their mental powers, and overwhelmed, as Faraday then was by the instant pressure of work in hand, and continued meditation on new experi- ments and prospective discoveries, would probably have consigned this application to the waste-paper basket. The tenth, perhaps, willing to discharge, at any rate, the claims of courtesy, might possibly have paid off the childish applicant with a few lines of cheap flattery in reply, or advised a round of elemen- tary experiments as ballast for his next sea venture, 144 THE FARADAY LECTURE. and so, at small cost, satisfied conscience. How does Faraday treat his boyish correspondent ? I hold in my hand the reply which the world-famed philosopher is at the trouble to write to the unknown youth, who, an unintroduced stranger, has addressed him. It is the original paper, and no copy, that I hold up before you ; those near me, you observe, recognise his handwriting at a glance, and I will read you the words, as they flowed from Faraday's pen : " Royal Institution, " 16th June, 1834. " Sir, " 1 have no hesitation in advising you to experiment in support of your views, "because, whether you confirm or confute them, good must come from your exertions. " With regard to the views themselves, I can say nothing about them, except that they are useful in exciting the mind to inquiry. A very brief consideration of the progress of experi- mental philosophy will show you that it is a great disturber of pre-formed theories. "I have thought long and closely about the theories of attraction and of particles and atoms of matter, and the more I think (in association with experiment) the less distinct does my idea of an atom or particle of matter become. " I am, Sir, " Your very obedient servant, "M. FARADAY." I have not a word of comment to offer on this noble letter of the master philosopher of the age to the boy whose young mind solicited his aid. My task, I feel, is now complete : so far, at least, THE FARADAY LECTURE. 145 as the narrow limits of my time and of my abilities have enabled me to make it so. Entrusted by your kind confidence with the duty of bringing to you my country's aid on this occasion, and naturally choosing for my theme the work of Germany's greatest chemist, Liebig, I have but rarely, and, so to speak, incidentally been able to ap- proach the subject of this evening's commemoration- Faraday. Nevertheless, more than one opportunity has presented itself of comparing, at intervals, the grandeur manifested alike in the noble natures, moral and intellectual, of these two ornaments of our day and generation ; and I indulge in the hope that, although it has been my task to lay before you the comprehensive life-work of the German chemist, the true object of this evening's meeting, viz., the cele- bration of the memory of the British physicist, has never been lost sight of. We have contemplated, if I may use this expression, in the portrait of the one the features of the other, and we separate with the unalterable conviction that, in whatever country of the world, in whatever epoch of futurity, mankind shall seek for models of a pure and noble human existence, no two exemplars will in any age stand forth more dignified by their intellectual work, more conspicuous for their moral beauty, than those whose names we have been commemorating this day MICHAEL FARADAY JUSTUS LIEBIG. HARRISON AND SONS, PRINTERS IN ORDINARY TO HER MAJESTY, ST MARTIN'S LANE. /S 4+.+^.^> /C*iWfc~ jf*-**; *+2 /L 5X > +"/ **-^ ^^^< --^>-^/<*x- > -* ^v /r %+ST &//(,**j /* +*^J CjC^/l*-* ** *& . /%* *-f*r~ + .+ < 0^*~^ 'fart+4*,^ >+t A5e^v r $-+**> ++*.+^<&_ ) J t*+~is'Z*~<> * # ,/X* <*., - ^KT^ r-it- ^ *~* 5^rv < *'*^^ t +*J> . /Zu*^. *^L^^ ^-x^e/ frs 5 / Ok^tr &' 4^-f.+r+> ^--//* *'" ^ / ^ ~-_j >,^^ t^ly ^L^ y^- '7 ^ _ ^ *-7^ '/* j_^ /-^lV / ^^- ^X ~ xi-~ **^ox~~> ><^. /- ^^^^^/^-A/; ^lir< tSS*^ t* *^c-^*->->^ &^3 >*t -* t**r^st*^. Xl- <-*** f* "~* ' _^ ~ t4 **r^rS ^ '4*~^**- ^fr /c 4^-e^5^^ 14 DAY USE 14 DAY USE RETURN TO DESK FROM WHICH BORROWED LOAN DEPT. This book is due on the last date stamped below, or on the date to which renewed. Renewals only: Tel. No. 642-3405 Renewals may be made 4 days priod to date due. Renewed books are subject to immediate recall. Due end of SPRING Quarter subject to recall after MAY 8072 9 BEfffrlB SEP 2 8- LD21A-60m-8,'70 (N8837slO)476 A-32 General Library University of California Berkeley