It seems fitting that these walls, which have vibrated in sympathy with that brilliant eulogy of Liebig, which Professor Hofmann pronounced some nine years ago, should hear something of him whose life-long association with Liebig has exercised an undying influence on the development of scientific thought. The names of Friedrich Wöhler and Justus Liebig will be linked together throughout all time. The work which they did in common marks an epoch in the history of chemistry. No truer indication of the singular strength and beauty of their relations could be given than is contained in a letter from Liebig to Wöhler, written on the last day of the year 1871. "I cannot let the year pass away," writes Liebig to Wöhler, "without giving thee one more sign of my existence, and again expressing my heartfelt wishes for thy welfare and the welfare of those that are dear to thee. We shall not for long be able to send each other New-Years' greetings, yet, when we are dead and mouldering, the ties which have united us in life will still hold us together in the memory of men as a not too frequent example of faithful workers who, without envy or jealousy, have zealously laboured in the same field, linked together in the closest friendship."

And yet, bound as they were in the ties of a friendship, the purity and warmth of which were but characteristic of the men, and although each influenced the other's walk and work in life to a degree which it is almost impossible to gauge, such was the strength of their individuality, and such the force of their genius that, without a doubt, either would have been a great figure in the history of science if the other had not existed.

The conditions under which minds of the highest type arise and develop have on more than one occasion engaged the attention of this audience. Although there were circumstances in Wöhler's surroundings which in early life may have influenced the bent of his mind, it is not easy to see whence sprang that passionate love of nature which was so strikingly exhibited in the man. His father, August Anton Wöhler, was formerly an equerry in the service of the Elector William II of Hesse; he afterwards came to live at Frankfort, and became a leading citizen of that town. His wise liberality and public spirit are commemorated in the Wöhler Foundation and Wöhler School, institutions known to every Frankforter. His mother was connected by marriage with the minister of Eschersheim, a village near Frankfort, and it was in the minister's house that Friedrich Wöhler first saw the light, on 31st July 1800. Even in early youth his passion for experimenting and collecting manifested itself, to the neglect not unfrequently of the lessons of the gymnasium; indeed, it would appear that during his school career Wöhler was not characterised by either special diligence or knowledge. The bent of his mind towards natural science was directed by Dr Buch, a retired physician, who had devoted himself to the study of chemistry and physics; and it was in the kitchen of his patron's house that he prepared the then newly-discovered element selenium, of which an account was afterwards sent by Dr Buch to Gilbert's Annalen, with Wöhler's name at the head of it. The elder Wöhler appears to have been a man of considerable artistic feeling, and under his direction the son was taught sketching, and otherwise educated in that perception of natural beauty which comes out so strikingly in his after life; and he was encouraged to make himself familiar with the literature which the genius of Schiller and Goethe has ennobled. He had, moreover, to thank his father for that love of physical exercise and passion for outdoor life which reacted so beneficially upon his development, and contributed so largely to the uniformly good health which he enjoyed to within a few days of his death. Mainly, it would seem, because his father had been there before him, Wöhler, in his twentieth year, entered the University of Marburg. It was his own and the family's wish that he should study medicine, and he accordingly put his name down for the lectures of B�nger on Anatomy, Gerling on Physics and Mathematics, and Wenderoth on Botany. He found time also to attend Ullmann's classes on Mineralogy; and although he declined to hear Wurzer's lectures on Chemistry, he by no means neglected that science. He transformed his living-room into a laboratory, and to the great, and perhaps not undeserved, disgust of his landlady, occupied himself with the preparation and study of the properties of prussic acid, thiocyanic acid, and other cyanogen compounds. He discovered at that time, without knowing that Sir Humphry Davy had anticipated him, the beautifully crystalline but intensely poisonous iodide of cyanogen; and in the little paper on cyanogen compounds which his good friend Dr Buch communicated to Gilbert's Annalen for him we have the first description of the remarkable behaviour of mercuric thiocyanate on heating, which has astonished and amused us in the so-called "Pharaoh's Serpent."

Wöhler, attracted by the fame of Leopold Gmelin, left Marburg for Heidelberg. His main idea was to hear the lectures of that distinguished man, but Gmelin declared this to be unnecessary and a waste of time. Wöhler in fact never attended any systematic lectures on chemistry; he had access, however, to the old cloisters which at that time constituted the Heidelberg laboratory, and there began the work on cyanic acid which, some four or five years later, was destined to culminate in the great discovery of the synthesis of urea. His association, at this time, with Tiedemann, who was engaged in physiological chemical investigations with Gmelin, has also considerable influence in determining the direction of much of his future work, whilst its immediate effect was the publication in Tiedemann's Zeitschrift f�r Physiology of the results of an inquiry into the transformation experienced by various substances, organic and inorganic, in their passage through the organism.

In 1823 Wöhler obtained his degree, when, on Gmelin's advice, he determined to follow his master's example, and abandon medicine for chemistry. At that time the great Swedish chemist Berzelius was at the summit of his fame; his masterly analytical skill, no less than his labours towards the development of chemical theory, had made him supreme among the chemists of Europe; and to Stockholm, therefore, Wöhler, acting on the advice of Gmelin, determined to go. He was warmly welcomed by Berzelius, on whom his communications to Gilbert's Annalen had made a favourable impression, and with the offer of a place in the private laboratory of the illustrious Swede, Wöhler set out for the Scandinavian capital. Of his experiences with Berzelius his pupil has left us a delightful description. It is valuable not only as a charming character-sketch of the great teacher, but also from the side-light it throws upon the nature and disposition of Wöhler himself. It is interesting, too, as an account of the mode in which Berzelius worked and taught, and as showing how the typical laboratory of that time contrasted with the temples which have since been reared by the disciples of Hermes.

"With a beating heart," says Wöhler, "I stood before Berzelius's door and rang the bell. It was opened by a well-clad, portly, vigorous-looking man. It was Berzelius himself... As he led me into his laboratory I was as in a dream, doubting if I could really be in the classical place which was the object of my aspirations... I was at that time the only one in the laboratory; before me were Mitscherlich and Heinrich and Gustav Rose; after me came Magnus. The laboratory consisted of two ordinary rooms furnished in the simplest possible way; there were no furnaces or draught places; neither gas nor water service. In one of the rooms were two common deal tables; on one of these worked Berzelius, the other was intended for me. On the walls were a few cupboards for the reagents; in the middle was a mercury trough, whilst the glass-blower's lamp stood on the hearth. In addition was a sink, with an earthenware cistern and tap, standing over a wooden tub, where the despotic Anna, the cook, had daily to clean the apparatus. In the other room were the balances, and some cupboards containing instruments; close to was a small workshop fitted with a lathe. In the neighbouring kitchen, in which Anna prepared the meals, was a small but seldom-used furnace and the never-cool sand-bath."

Wöhler's first exercises were in mineral analysis, made in order that he might become acquainted with Berzelius's special methods and manipulative procedure. At that time he prepared, among other products, some new compounds of tungsten, notably the beautifully crystallised monoxychloride, and the tungsten sodium-bronze (Na2W3O9), which, some twenty-five years later, was introduced into the arts as a bronze powder. It was, however, with his investigation on cyanic acid that both he and Berzelius were mainly interested. To Berzelius the existence of this body was of importance from the light it seemed to him to throw upon the validity of the new chlorine theory. "I was surprised," says Wöhler, "to hear him, the hitherto steadfast upholder of the old notion, now always talk of chlorine instead of  'oxidised hydrochloric acid.' Once, when Anna, in cleaning some vessel, remarked that it smelt strongly of oxymuriatic acid, Berzelius said, 'Hearest thou, Anna; thou must no longer speak of oxidised muriatic acid; thou must call it chlorine; that is better.'" With what feelings would Davy have listened to that colloquy between the Swedish philosopher and his factotum! Chlorine was discovered by Berzelius's countryman, Scheele, but its true nature was first demonstrated in the laboratory of the Royal Institution.

A couple of months were now spent in travel with Berzelius, in company with the two Brongniarts, Alexandre the geologist and Adolphe the botanist, during which they explored the greater portion of the geologically interesting parts of Southern Sweden and Norway, and collected rich stores of those wonderful minerals for which Scandinavia is famous. Scandinavia is no less famous for salmon and trout; and it was on his return from a fishing expedition in Norway that the travellers met with Davy, who, as readers of Salmonia know, handled his rod with great zest and skill. Wöhler, who as a boy had learned the story from his friend Dr Buch of the isolation of the alkali metals by Davy, and who, aided by his little sister, whose business it was to blow the bellows, had toiled, not unsuccessfully, to make potassium in the kitchen fire, was presented to the famous chemist.

At the end of the tour Wöhler took leave of Berzelius and returned to Germany. Of his association with the great teacher Wöhler had ever the kindliest memories. Although the outcome of much of his subsequent work, or at least much of that which he did in concert with Liebig, might be said to bring him in occasional conflict with Berzelius's cherished convictions on points of chemical theory, the master and pupil remained to the end in ties of the warmest friendship. Scarcely a month passed without an exchange of letters. Those from Berzelius were carefully preserved by Wöhler, who, after his master's death in 1848, presented them, to the extent of some hundreds, to the Swedish Academy of Sciences. We are told that in the later letters the "trauliche Du" appears in place of the more formal "Sie," and that Totus et tantus tuus is a not unfrequent signature.

Wöhler's gratitude and almost filial reverence are seen in the circumstance that even in the full tide of his vigour, and when time was doubly precious to him, he continued to charge himself with the yearly translation of Berzelius's Jahresbericht into German. It is easy to trace the influence of Wöhler's contact with Berzelius in his after-work. To begin with, the men had much in common; their sympathies were as catholic as science itself, and they ranged at will over every department of chemical knowledge. Wöhler attacked the composition of a mineral with as much ardour as he did the preparation of an organic compound; to him the problems of physiological chemistry were not more important than the isolation of a rare earth or the perfection of some analytical method. The artificial barriers and arbitrary lines of demarcation in the science seemed to have no existence for him; indeed, it was the crowning triumph of his work to break down such barriers almost at a stroke, and to demonstrate the irrationality of attempts to draw distinctions in the absence of differences. The history of chemistry is indeed like that of the nation which has done so much to advance it; its unity to-day is as complete as that of Germany itself.

Wöhler, now back again in Germany, prepared to embark on his academic career, and on the advice of Gmelin and Tiedemann he decided to settle in Heidelberg as a privat docent. But to Heidelberg he was not destined to go. His work had already been gauged by Leopold von Buch, Poggendorff, and Mitscherlich, and these, without his knowledge, strongly recommended that he should be elected to the vacant teachership of chemistry in the newly-founded Trade School in Berlin. Berzelius advised him to accept the post, and accordingly to Berlin Wöhler went in 1825. He was now in possession of a laboratory which he could call his own, and he had to justify that possession by the use which he made of it. One of the problems which he at this time attacked was the isolation of aluminium, a metallic radicle more abundant and more widely diffused than any other of the fifty substances we are accustomed to designate as metals. He succeeded in obtaining the metal by the method which, nearly twenty years later, was worked out on a manufacturing scale by Sainte-Claire Deville. Deville caused the first bar of aluminium thus procured to be struck into medals, with the image of Napoleon III on the one side, and the name Wöhler with the date 1827 on the other, and some time afterwards the Emperor simultaneously designated the two chemists officers of the Legion of Honour.

But of the twenty-two memoirs and papers which Poggendorff's Annalen exhibits as the outcome of Wöhler's activity and power of work during his six years' stay in Berlin, that on the artificial formation of urea is by far the most important. No single chemical discovery of this century has exercised so great an influence on the development of scientific thought, and the words with which Wöhler closes his account of the molecular transformation of ammonium cyanate - a body of purely inorganic origin - into urea - a substance which of all that might be named is most characteristic of the action of the so-called vital force - are full of meaning:

"This unexpected result," he says, "is a remarkable fact, in so far as it presents an example of the artificial formation of an organic body, and indeed one of animal origin, out of inorganic materials." "The synthesis of urea," says Professor Hofmann in his account of Wöhler's life-work, "was an epoch-making discovery in the real sense of that word. With it was opened out a new domain of investigation, upon which the chemist instantly seized. The present generation, which is constantly gathering such rich harvests from the territory won for it by Wöhler, can only with difficulty transport itself back to that remote period in which the creation of an organic compound within the body of a plant or an animal appeared to be conditioned in some mysterious way by the vital force, and they can hardly realise the impression which the building up of urea from its elements then made upon men's minds. And yet it cannot be said that chemists were unprepared for this discovery. Men were long ago in the habit of perceiving that bodies of mineral origin were but the types of those met with in the animal and vegetable organism - in both classes there were the same differences in states of aggregation, the same mutual transformations, the same crystalline forms, the same constancy in combining relations the same conjunction of the elements according to the weights of their atoms or in multiples of these, in both classes the appearances of the same species of compounds. But all attempts to build up organic compounds from their elements, as this for a large number of mineral substances had already been done, had hitherto been futile. The chemists of that period had nevertheless the presentiment that even this barrier must fall, and one can conceive the feeling of joy with which the gospel of a new unified chemistry was hailed by the intellect of that time. With the revolution thus effected in the ideas of men, science was directed into new paths and unto new goals. Who does not know with what zeal these paths have been trodden, and how many of these goals have been reached!"

But if at this time Wöhler made a great discovery for the world, he also, at about the same time, made a great discovery for himself: he found Liebig. The manner in which the two men were brought together is worth mentioning, for it would seem almost as if the hand of destiny was in it. At about the period that Wöhler was in Stockholm thinking and working on cyanic acid, Liebig was in Paris engaged with Gay Lussac in the study of the metallic compounds of fulminic acid, which obtains its not inappropriate name on account of the formidable explosive character of its salts. Liebig, with rare skill and courage, had determined the composition of that acid, and had been rewarded by the honour of a waltz with Gay Lussac, it being the habit of that distinguished philosopher, as he explained to the astonished young German doctor, to express his ecstasy on the occasion of a new discovery in the poetry of motion. But the most extraordinary result of that investigation was to show that the terribly explosive fulminic acid and the innocuous cyanic acid were of identical composition. The idea that bodies could exist of identical ultimate composition - that is, composed of the same elements united in the same proportion - and yet possess essentially different properties - in other words be absolutely dissimilar things - was new to science. Berzelius, the great chemical lawgiver of his time, scouted the notion as absurd; to him it was impossible to conceive that identity in elementary composition should not result in identity of properties. And yet, later on, Berzelius was forced to realise the fact by Wöhler's discovery of the molecular transformation of ammonium cyanate into urea, and to coin for us the word isomerism, by which that fact is denoted.

It was thus, from the singular circumstance that Wöhler and Liebig were at the outset of their careers engaged upon the elucidation of the nature of two bodies of identical composition, but of dissimilar origin, dissimilar relations, and very different properties, that they were brought into juxtaposition. They desired to know each other; they met in the house of a mutual friend at Frankfort, and henceforth the names of Liebig and Wöhler became linked together for all time.

The origin of the partnership, so fruitful in consequences for science, may be seen from the following characteristic letter:

FRIEDRICH WÖHLER TO JUSTUS LIEBIG.

Sacrow, near Potsdam, 8th June 1829

Dear Professor - The contents of your last letter to Poggendorff have been communicated to me by him, and I am glad that they afford me an opportunity of resuming the correspondence which we began last winter. It must surely be some wicked demon that gain and again imperceptibly brings us into collision by means of our work, and tries to make the chemical public believe that we purposely seek these apples of discord as opponents. But I think he is not going to succeed. If you are so minded, we might, for the humour of it, undertake some chemical work together, in order that the result might be made known under our joint names. Of course, you would work in Giessen and I in Berlin, when we are agreed upon the plan, and we could communicate with each other from time to time as to its progress. I leave the choice of subject entirely to you.

I am very glad that you have also determined the identity of pyrouric acid, and cyanic [cyanuric] acids. L. Gmelin would say: "God be thanked, there is one acid the less!"...

Yours, Wöhler.

Liebig acceded to the proposition at once, and suggested some problem on the chemical nature of nitrogen; this Wöhler found himself unable to undertake, as it involved the use of chlorine, to the action of which he was at all times extremely susceptible. On the other hand, he proposed to Liebig that they should continue in common a research on mellitic acid, which he had himself begun. Their joint investigation on this body made its appearance in the course of the following year.

It would be quite impossible within the limits of an hour to attempt to give you anything approaching to a complete analysis of Wöhler's work. In all, he was the author of 275 memoirs and papers, and of these fifteen were published in concert with Liebig. I must therefore confine my selection from this vast amount of material to those papers which are of paramount importance by reason of the influence which they have exerted on chemical theory or on the development of the chemical arts.

Very shortly after the publication of the work on mellitic acid, Wöhler proposed to Liebig a joint investigation on cyanuric acid, in the course of which he observed the extraordinary transformation of that acid into cyanic acid, and the reconversion of the cyanic acid into cyanuric acid - one of the most remarkable instances of molecular rearrangement known to the chemist. The work progressed little for some months, owing to the demands made by Berzelius's Jahresbericht on Wöhler's time. "Wirf die Schreiberei zum Teufel," wrote Liebig, "und gehe in das Laboratorium, wohin Du geh”rst." In due time, doubtless, that functionary carried off the writing to his master, the printer, and Wöhler went back to his laboratory, and in a few weeks the two investigators obtained the clue to the puzzle. Liebig wrote to Wöhler: "Now that I have received your experiments, the whole thing is cleared up, and with what satisfaction for us! The matter is now decided; the cyanic acid of Serullas is identical with that from urea... Ich bin ganz n„rrisch vor Freude, dass unser Kindlein nun fehleros in die Welt gesetzt wird, ohne Buckel oder Klumpfuss."

It had been suggested to attack the fulminic acid again. "The fulminic acid we will allow to remain undisturbed. Like you, I have vowed to have nothing more to do with this stuff. Some time back I wanted, in connection with our work, to decompose some fulminating silver by means of ammonium sulphide; at the moment the first drop fell into the dish the mass exploded under my nose. I was thrown backwards, and was deaf for a fortnight, and became almost blind."

The work on cyanic acid appeared in Poggendorff's Annalen during the last month of 1830, and Wöhler was able to send the "Kindlein" "im neuen Kleide," as he says, with a New Year's greeting to his friend. Liebig had suggested fresh work, but at the moment Wöhler was in no humour to attack anything organic. The Swedish chemist Sefstr”m had just announced the existence of a new element in the slag of certain iron ores, and this very substance had slipped through Wöhler's fingers unperceived. "I was an ass," he wrote to his friend, "not to have detected it two years ago in the lead ore from Zimapan in Mexico. I was busy with its analysis, and had found something strange in it, when I was laid up for some months in consequence of breathing hydrofluoric acid, and so the matter was allowed to rest. Meanwhile Berzelius sends me word of its discovery by Sefström in Swedish bar iron and in slag. It is very like chromium, and just as remarkable. Moreover, it is the same metal that Del Rio found in the Mexican lead ore, and called erythronium: Descotils, however, had declared this ore to be lead chromate."

Wöhler, no doubt, found a ready sympathiser in Liebig, to whom, not many years before, a similar experience had happened. We all know the story of the young chemist whose unscientific use of the imagination cost him the discovery of the element bromine. Wöhler had sent some of the substance from the Zimapan ore to Stockholm, and Berzelius wrote as follows:

JAKOB BERZELIUS TO FRIEDRICH WÖHLER

Stockholm, 22nd January 1831.

As to the small quantity of the body marked ? I will relate the following story: "In the far north there lived in the olden time the goddess Vanadis, as beautiful as she was gracious. One day there came a knock at her door. The goddess was in no hurry, and thought, 'They can knock again'; but no further knock came, for he who knocked had passed on. The goddess, wondering who it could be that cared so little to be let in, ran to the window and recognised the departing one. 'Ah!' said she to herself, 'it is that lazy fellow Wöhler! He richly deserves his name, since he cares so little to come in.' Some days after, some one else knocked, repeatedly and loud. The goddess opened the door herself; it was Sefström who entered, and, as a consequence vanadium came to light." Your specimen with the ? is, in fact, vanadium oxide.

But he that has found the mode of artificially forming an organic body can well renounce the discovery of a new metal; indeed, one might have discovered ten unknown elements without as much skill as is seen in the masterly work which you and Liebig have carried out together and have just communicated to the scientific world.

In 1831 Wöhler was called from Berlin to Cassel, and for some little time he was wholly engaged in the planning and erection of his new laboratory at the Gewerbe-Schule in that town. In the spring of the following year he was again ready for a new research; and this time it was to be the most fruitful piece of work that the two investigators jointly engaged in. It was, in fact, to be the classical research on bitter almond oil. On 16th May 1832 Wöhler wrote to Liebig: "Ich sehne mich nach einer ernten Arbeit, sollten wir nicht die Confusion mit dem Bittermandel”l in's Reine bringen? Aber woher Material?" It must have been something akin to inspiration which led Wöhler to take up this subject; but neither he nor Liebig could have been wholly conscious of the consequences which were to follow from their work. Today oil of bitter almonds is made artificially in Germany by the hundredweight; at that time the investigators could only obtain it in small quantities from Paris. They had indeed to thank Pelouze for the material with which they worked. Wöhler made this, his greatest research, under the cloud of a great sorrow; after barely two years of married life he lost his wife. Liebig, in the tenderest manner, brought him over to Giessen, and sought to win him from his grief and the sense of his loneliness by his company and the wholesome distraction of their joint work, done side by side.

On 30th August 1832 Wöhler wrote to Liebig from Cassel:

"I am here back again in my darkened solitude. I do not know how I shall thank you for the affection with which you received me and kept me by you for so long. How happy was I that we could work together face to face.

"I send you with this the memoir on bitter almond oil. The writing has taken me longer than I anticipated. I want you to read through the whole with the greatest care, and to notice particularly the numbers and formulae. What does not please you, alter at once. I have often felt that there was something not quite right, without being able to detect what was wrong."

The investigation on the radicle of benzoic acid will ever remain one of the greatest achievements in the history of organic chemistry

I shall not attempt to dwell upon the outcome of this great work. The investigation on the radicle of benzoic acid will ever remain one of the greatest achievements in the history of organic chemistry; the work was indeed epoch-making in the far-reaching nature of its consequences. It was full of facts and rich in the promise of new material - a veritable mine from which subsequent workers like Cannizzaro, Fehling, Piria, Stas, and Hlasiwetz have dug rich treasure. The immediate effect of the paper was to establish the doctrine of organic radicles by demonstrating the existence of groups of bodies which had their analogues and prototypes in inorganic chemistry. The concluding words of the memoir strike, in fact, the keynote of the whole investigation. "In once more reviewing and connecting together the relations described in this memoir," so wrote Liebig and Wöhler, "we find that they may be grouped round a common nucleus which preserves intact its nature and composition in its associations with other bodies. This stability has induced us to regard this nucleus as a kind of compound element, and to propose for it the special name of 'benzoyl.'"

A significant feature in the memoir was that each of the substances described and correlated was the type of a distinct group of bodies, some of which were known, but of which the analogies and relations were unperceived; others of these bodies were yet to be discovered, a matter of little difficulty when the modes of their origin had been indicated. The effect of this memoir on the chemical world was instantaneous. Berzelius was delighted. "The facts put forward by you," he wrote to Wöhler and Liebig, "give rise to such considerations that they may well be regarded as the dawn of a new day in vegetal chemistry. On this account I would propose that this first discovered radicle composed of more than two elements should be named proin (from ã


,the beginning of day) or orthrin (o


o
, daybreak), terms from which names like proic acid, orthric acid, proic chloride, orthric chloride, etc., could be readily derived."

Wöhler remained in Cassel for nearly five years. In the autumn of 1835 died Stromeyer, Professor of Chemistry in the University of Göttingen. Opinions were divided as to his successor; the choice lay between Liebig and Wöhler. Eventually Wöhler was selected, and entered on his work at Göttingen in the early part of 1836. He was succeeded at Cassel by Bunsen, who was at that time privat docent in G”ttingen. In the October of that year Wöhler was again ready for fresh work. He writes to Liebig:

"I am like a hen which has laid an egg and straightway sets up a great cackling. I have this morning found how oil of bitter almonds containing prussic acid may be obtained from amygdalin, and would propose that we jointly undertake the further investigation of the matter, as it is intimately related to the benzoyl research, and it would seem strange if either of us should work alone again in this field, denn es lässt sich gar nicht absehen wie weit es sich erstreckt, und ich glaube es ist gewiss fruchtbar, wenn es mit Deinem Mist gedüngt wird..." In a couple of days afterwards Wöhler was ready with the fundamental facts which constituted the basis of the research, and had sketched out its plan. He writes:

"I have just made a most remarkable discovery in relation to the amygdalin. Since it appeared that bitter almond oil might be obtained from amygdalin, it occurred to me that the one might be converted into the other by simply distilling almonds with water by an action similar to that of a ferment upon sugar, the change in this case being due, in all probability, to the albumen in the almonds. And this idea seems to be completely established. The facts are as follows:

"1. Amygdalin, dissolved in water and digested with a bruised sweet almond, begins almost immediately to smell of bitter almond oil, which after a time may be distilled off in such quantity that it would appear that the amygdalin was wholly transformed into it.

"2. A filtered emulsion of sweet almonds produces the same effect.

"3. A boiled emulsion of sweet almonds, in which, therefore, the albumen is coagulated, affords not the smallest trace of oil with amygdalin.

"4. Bruised sweet almonds, covered with alcohol, and freed therefrom by pressure, transform, as before, amygdalin into bitter almond oil.

"5. Bruised peas, or the albumen they contain, give no oil with amygdalin.

"There are three points, therefore, to be ascertained -

"a. What is the substance in bitter or sweet almonds which, in contact with amygdalin and water, forms bitter almond oil?

"b. Is the action by double decomposition or catalytic, like that of a ferment?

"c. What is the other product which, in all probability, is formed in addition to the oil and prussic acid?"

The merest tyro in organic chemistry today is familiar with the broad features of this investigation, and knows the answers which Liebig was able to give to his friend's interrogatories. The third substance Liebig discovered to be sugar. Under the influence of a nitrogenised ferment, termed by Liebig and Wöhler emulsin, amygdalin, in presence of water, is decomposed into benzaldehyde (bitter almond oil), in prussic acid, and sugar (glucose), thus:

C20H27NO11 + 2H2O = C7H6O + CNH + 2C6H12O6

Amygdalin Water Benzaldehyde Prussic Acid Glucose

It simply remains to explain why this reaction only occurs when the almonds are bruised and digested with water. Both the emulsin and the amygdalin exist together in the almonds, but are contained in separate cells, and are only brought into contact by the rupture of the cell walls and the solvent action of the water. Amygdalin was the prototype of a large and important group of substances now classed together as the glucosides.

At the instigation of Wöhler, the friends again returned to the question of the chemical nature of uric acid, and the memoir which they eventually published on the subject is of the profoundest interest, not only to the chemist, but also to the physiologist. Uric acid, originally discovered by Scheele, was shown, in 1815, by William Prout, then a boy of nineteen, to be the main constituent of the solid excreta of reptiles; other chemists had succeeded in obtaining various derivatives from it; indeed, Prout himself had prepared from it the so-called purpuric acid, a substance which years after, as murexide, obtained a transitory importance in the arts as a colouring matter. But nothing was known concerning the constitution of the body or of its relations to its derivatives until Wöhler and Liebig attacked the problem. The extraordinary mutability of uric acid, which had baffled and deceived previous investigators, was to Wöhler and Liebig the clue to a labyrinth leading to a veritable treasure-house, and the wonderful insight and rare analytical skill of these two great men were never more clearly indicated than in the way in which they trod this intricate maze. No fewer than fifteen new bodies were added to the list of chemical compounds, and these were correlated with the same masterly lucidity that was so strikingly exhibited in the memoir on the radicle of benzoic acid. Some of the greatest triumphs of modern chemistry are seen in the synthesis of organic bodies. That organic chemistry was about to advance along this line was clearly foreseen by Wöhler and Liebig. In opening their account of this, the last great work they did in common, they say:

"From this research the philosophy of chemistry will draw the conclusion that the ultimate synthetical formation in our laboratories of all organic bodies, in so far as they are not organised (in so weit sie nicht mehr dem Organismus angehören), may be regarded as not only probable but as certain. Sugar, salicin, morphin will be artificially obtained. As yet we know nothing of the way by which this result is to be attained, inasmuch as the proximate materials for forming these bodies are unknown; but we shall come to know them."

Henceforth the friends worked but little together. Liebig's energies were spent in other directions, and Wöhler turned his attention to inorganic chemistry. Time allows only the very briefest mention of his more important discoveries in this department of the science. We have first his isolation of crystalline boron, and the preparation of the compounds of boron with aluminium and nitrogen, work done in concert with Sainte-Claire Deville. The readiness with which boron unites with nitrogen, and the mode in which the compound may be decomposed, led Wöhler to a conception of the origin of boric acid and borax in the volcanic waters in which they are frequently found. In collaboration with Buff he discovered the spontaneously inflammable hydride of silicon, the analogue of marsh gas, the simplest of the hydrides of carbon, and thereby laid the foundation-stone of a superstructure, which in time to come may be only less imposing than that built up of the compounds of carbon. Many years ago Wollaston noted the presence in the slags from the iron blast-furnaces of beautiful lustrous copper-coloured cubes, which he assumed to be metallic titanium; Wöhler proved this substance to be a compound of carbon, nitrogen, and titanium, and showed how it might be obtained.

Of all the elements known to the chemist up to the period of Wöhler's cessation from work, it may be safely averred that there was not one but had passed through his hands in some forms or other.

Of all the elements known to the chemist up to the period of Wöhler's cessation from work, it may be safely averred that there was not one but had passed through his hands in some forms or other. Now he was busy with chromium, then with cerium, next with uranium and the platinum metals; titanium, tantalum, thorium, thallium, tungsten - all came in for some share of his attention. Of the minerals and meteorites he analysed the number is legion; indeed, as Professor Hofmann says, whoever sent him a piece of meteoric iron gained his heart. His untiring activity was a continual source of wonder to his friends. "How happy art thou in thy work!" wrote Liebig on one occasion; "thou art like the man in the Indian fable who, when he laughed, dropped roses from his mouth."

The names of Liebig and Wöhler are now so closely intertwined in the history of chemistry that it is hardly possible to avoid comparing the men. Such a comparison has already been drawn by one who of all

others is most fitted to draw it. "Liebig," says Dr Hofmann, "fiery and impetuous, seizing a new thought with enthusiasm, and giving to it the reins of his fancy, tenacious of his convictions, but open to the recognition of error, sincerely grateful, indeed, when made conscious of it, - Wöhler, calm and deliberate, entering upon a fresh problem after full reflection, guarding himself against each rash conclusion, and only after the most rigorous testing, by which every chance of error seemed to be excluded, giving expression to his opinion, - but both following the path of inquiry in their several ways, and both animated by the same intense love of truth! Liebig, irritable and quick to take offence, hot-tempered, hardly master of his emotions, which not unfrequently found vent in bitter words, involving him in long and painful quarrels, - Wöhler, unimpassioned, meeting even the most malignant provocation with an immovable equanimity, disarming the bitterest opponent by the sobriety of his speech, a firm enemy to strife and contention, - and yet both men penetrated by the same unswerving sense of rectitude! Can we marvel that between two such natures, so differently ordered, and yet so complementary, there should ripen a friendship which both should reckon as the greatest gain of their lives?"

Who can fully gauge the influence of such a personality as W”hler's? How it was exerted on Liebig is indicated in the following letter:

FRIEDRICH WÖHLER TO JUSTUS LIEBIG

Göttingen, 9th March 1843

To make war against Marchand, or, indeed, against anybody else, brings no contentment with it, and is of little use to science... Imagine that it is the year 1900, when we are both dissolved into carbonic acid, water, and ammonia, and our ashes, it may be, are part of the bones of some dog that has despoiled our graves - who cares then whether we have lived in peace or anger; who thinks then of thy polemics, of the sacrifice of thy health and peace of mind for science? - Nobody. But thy good ideas, the new facts which thou hast discovered, these, sifted from all that is immaterial, will be known and remembered to all time. But how comes it that I should advise the lion to eat sugar?

It was thus in philosophic contentment, happy in his work, in his home life, and in his friendships, that Wöhler lived out his fourscore years and two. He made Göttingen famous as a school of chemistry; at the time of the one-and-twentieth year of his connection with the university it was found that upwards of 8000 students had listened to his lectures or worked in his laboratory. There was hardly an academy of science or a learned society which did not in some way or other recognise his services to science. He was made a Foreign Member of the Royal Society in 1854, a Corresponding Member of the Berlin Academy in 1855, Foreign Associate of the Institute of France in 1864, and in 1872 he received the Copley Medal from the Royal Society. He died on 23rd September 1882.