March 20, 1884J 



NATURE 



493 



Wohler remained in Cassel for nearly five years. In the 

 autumn of 1835 died Stromeyer, Profes or of Chemistry in the 

 Univeisity of Gottingen. Opinions were divided as to his suc- 

 ce;sor ; the choice lay between Liebiij and Wohler. Eventually 

 Wohler was selected, and entered on his woric at Gottingen in 

 the early part of 1836. He was succeeded at Cassel by Bunsen, 

 » ho was at that time pnvat decent in Gottingen. In the Octo- 

 ber of that year Wohler was again ready for fresh work. He 

 writes to Liebig : " I am lilie 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 ob- 

 tained from amygdalin, and would propose that we jointly 

 undertake the further investigation of the matter, as it is inti- 

 mately related to the benzoyl research, and it would seem 

 strange if either cf us should work alone again in this field, 

 denn es lasst sich gar nicht absehen wie weit es sioh erstreckt, 

 und ich glaube es ist gewiss fruchtbar, wenn es mit Deinem Mist 

 gediingt wird. ..." In a couple of days afterwards Wohler 

 was ready with the fundamental facts for the research and had 

 sketched out its plan. He writes : — 



"I have just made a most remarkable discovery in re- 

 lation 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 : 



"I. Amygdalin, dissolved in water and digested with a 

 bruised sweet almond, begins almost immediately to smell of 

 bitter almond oil, « hich 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. 



"i3. 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 — 

 "<7. What is the :^ubstance 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 ? 



"r. 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 to-day 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 

 Wohler emulsiii, amygdalin, in presence of|wd'er, is decom- 

 posed into benzaldehyde (bitter almond oil), prussic acid, and 

 sugar (glucose), thus : — 



CsoH^NOii -(- 2H2O = Ci,HsO -I- CNH -t- 2C^\\.,^0^. 

 Amygdalin Water Benzaldehyde Prussic Glucose 



acid 

 It simply remains to explain why this reaction only occurs 

 when the almonds are bruised and digested \vith 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 classed together as the glucosides. 



At the instigation of Wohler, 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 pro- 

 foundest interest, not only to the chemist, but also to the physio- 

 logist. Uric acid, originally discovered Ijy Scheele, was shown 

 in 1815, by William Prout, then a bay 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 mure.xide 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 Wohler and Liebig attacked the problem. 

 The extraordinary mutability of uric acid, which had baffled and 

 deceived previous investigators, v\as to Wohler and Liebig the 

 very clue to the labyrinth leadin;^ 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 

 .-trikingly 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 

 Wohler and Liebij. In opening their account of this the last 

 great work they did in common, they say: — "From this re- 

 search, 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 angehtiren), 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 in common. Liebig's 

 energies were spent in other directions, and Wohler turned his 

 attention to inorganic chemistry. Time allows only the very 

 briefest mention to be made of his more impoi-fant 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-Cliire Deville. The readiness with which boron unites 

 with nitrogen, and the mode in which the compound may be 

 decomposed, led Wohler to a conception of the origin of boric 

 acid and borax in the volcanic waters in which they are fre- 

 quently 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 

 CO Le may only be less imposing than that built up of the com- 

 pounds of carbon. Many years ago Wollaston noted the 

 presence of beautiful lustrous copper-coloured cubes in the 

 slags from the iron blast-furnaces, which he assumed to be 

 metallic titanium ; Wohler proved this substance to be a com- 

 pound of carbon, niti'ogen, and titanium, and showed how it 

 might be obtained. Of all the elements known to the chemist up 

 to the period of Wohler's cessation from W'ork, it may be safely 

 averred that there was not one but had passed through his 

 hands in some form or other. Now he was bu-y with 

 chi'omium, then with cerium, next with uranium and the 

 platinum mel als ; 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 Pi of. Hofmann says, whoever sent him a piece of 

 meteoric iron gained his heart. His restless activity w;is a 

 source of contiimal 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 ro-e 

 from h's mouth." 



The names of Liebig and Wohler are now so closely inter- 

 twined in the history of chemistry that it is hardly possib'e ti 

 avoid comparing the men. Such a comparison has already been 

 drawir by one who of all others is most fitted to c'raw it. 

 " Liebig," says Dr. Hofmann, "fiery and impetuous, se'zing a 

 new thought with enthusiasm, and giving to it the reir.s of his 

 fancy, tenacious of his convictions, but open to the recognition 

 of error, sincerely grateful, indeed, when made conscious of it,— 

 Wohler, calm and deliber-ate, entering upon a fresh probi m 

 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 follow ing 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, — Wohler, 

 unimpassioned, meeting even the mo^t malignant provocation 

 with an immovable equanimity, disarming the bitterest opponent 

 by the sobriety of his speech, a firm enemy to strife and conten- 

 tion — and yet both men penetrated by the same unswerving 



