169 VICTOR MEYER MEMORIAL LECTURE, (DELIVERED ON FEBRUARY 8th, 1900). By T. E. TRORPE, Ph.D., D.Sc., LL.D., F.R.S., President of the Chemical Society. BY the untimely death of Victor Meyer, on August Sth, 1897, under circumstances of peculiar sadness, and at the comparatively early age of forty-nine, our sister Society in Berlin lost her President of the year, and, at the same moment, we were deprived of one of the most brilliant of that band of eminent men whom we distinguish as our Honorary Foreign Members. The Council have deemed it fitting that the attempt should be made to put on record our appreciation of the remarkable services Victor Meyer rendered to the science which he cultivated, during the all too short period of his activity, with such striking assiduity and success.As a friend of nearly thirty years’ standing, and as one who worked, literally, side by side with him in the famous laboratory which he lived t o direct, and died whilst directing, I have charged myself with the execution of this duty. Of Meyer’s early life-that is, of the period before I first knew him at Heidelberg as a girlish-looking, bright-eyed youth, quick of movement and active in thought, ready and fluent of speech, full of zeal, and intensely interested in the higher work of the place-I know little, beyond that he was born in Berlin and was the son of a calico manufacturer.* Once, in the course of some discussion on the characteristic differenues in the school training of English and German lads, he made reference to his own experiences in the gymna- sium, from which I gathered that his inclination towards science was in nowise shaped by what he saw or heard i n early youth.Nor, so far as can be determined, was there anything in his home life which inclined him to take to chemistry. I n the case of many who have become eminent in physical science-and doubtless also in the case of more who have not-their first love has sprung from the passion of experimenting. But at this time Meyer, apparently, had neither the opportunity nor the desire to make experiments. Indeed, the home atmosphere tended to make him literary or artistic. There can be no doubt that he owed to this environment, and more especially to the example and precept of his mother, herself a woman of considerable intellectual power, certain strongly marked features of character which * The date of his birth was September 8th, 1848. VOL.LXXVII. 0169 VICTOR MEYER MEMORIAL LECTURE, (DELIVERED ON FEBRUARY 8th, 1900). By T. E. TRORPE, Ph.D., D.Sc., LL.D., F.R.S., President of the Chemical Society. BY the untimely death of Victor Meyer, on August Sth, 1897, under circumstances of peculiar sadness, and at the comparatively early age of forty-nine, our sister Society in Berlin lost her President of the year, and, at the same moment, we were deprived of one of the most brilliant of that band of eminent men whom we distinguish as our Honorary Foreign Members. The Council have deemed it fitting that the attempt should be made to put on record our appreciation of the remarkable services Victor Meyer rendered to the science which he cultivated, during the all too short period of his activity, with such striking assiduity and success.As a friend of nearly thirty years’ standing, and as one who worked, literally, side by side with him in the famous laboratory which he lived t o direct, and died whilst directing, I have charged myself with the execution of this duty. Of Meyer’s early life-that is, of the period before I first knew him at Heidelberg as a girlish-looking, bright-eyed youth, quick of movement and active in thought, ready and fluent of speech, full of zeal, and intensely interested in the higher work of the place-I know little, beyond that he was born in Berlin and was the son of a calico manufacturer.* Once, in the course of some discussion on the characteristic differenues in the school training of English and German lads, he made reference to his own experiences in the gymna- sium, from which I gathered that his inclination towards science was in nowise shaped by what he saw or heard i n early youth.Nor, so far as can be determined, was there anything in his home life which inclined him to take to chemistry. I n the case of many who have become eminent in physical science-and doubtless also in the case of more who have not-their first love has sprung from the passion of experimenting. But at this time Meyer, apparently, had neither the opportunity nor the desire to make experiments. Indeed, the home atmosphere tended to make him literary or artistic. There can be no doubt that he owed to this environment, and more especially to the example and precept of his mother, herself a woman of considerable intellectual power, certain strongly marked features of character which * The date of his birth was September 8th, 1848.VOL. LXXVII. 0170 THORPE : VICTOR MEYER MEMORIAL LECTURE, are not usually associated with men of science. According to his friends Liebermann and Jacobson, his own wish was to become an actor, and that he would have succeeded in such a profession is highly probable. He had, indeed, all the natural gifts of the born actor- dramatic sense, emotional power, a fine voice, an impressive manner, and a handsome presence. When he became a teacher of chemistry, these attributes were turned to good account. His early love of declamation, combined with his elocutionary ability, eventually made him one of the most striking and effective lecturers in Germany.The traditions of the University lecture-theatre no doubt exercised their restraining influence, but Meyer was too much under the sway of his artistic temperament and too impatient of conven- tionality to repress altogether his natural bent. Moreover, he was not insensible to the effect he created, or unmindful of the influence he gained, when, t o use the common phrase, he (‘let himself go,” and by his trenchant, impressive language, and the brilliancy of his illus- tration, communicated something of his own enthusiasm to even the most listless of back-bench men. This power of exposition was quickly perceived, and no doubt its early recognition served to bring him the more speedily to the front.At Heidelberg, as in many other centres of chemical instruction, there was a small Chemical Society, composed of the Extraordinary Professors, the Privat-docenten, and assistants, together with the senior or more active students i n the various laboratories who were elected into it by favour of the teachers. I n my time it numbered amongst its members Erlenmeyer, Ladenburg, Horstmann, Ludwig, Cohen (the mineralogist), Rose, and Emmerling. Its president was Bunsen, and the occasions on which he took the chair were the red-letter days of the session. We invariably sent him home happy, his pockets filled with all the good champagne corks we could collect. The formal business of the Society-if formal it can be called-was preceded by an Abend- essen, and if not accompanied, at least succeeded, by a considerable mani- festation of ‘‘ das gemuthliche Element.” No man was more popular at these gatherings than Meyer.His nimble mind and retentive memory, his gift of ready speech, his sense of humour and genial manner combined to make it pleasant to listen to him no matter whether he was, in accordance with the rules of the Society, called upon to give an account of some work which had just been published, or whether he was discussing and criticising a communication from a fellow member. From time to time we had reports of the condition of such investigations as were in progress in the Heidelberg laboratories, or of which the results were to appear in the forthcoming issue of the Annalen, for, at the period of which I write, the Berichte was a thin and puny pub- lication, hardly out of its swaddling clothes, and with little sign of theTHORPE : VICTOR MEYER MEMORIAL LECTURE.171 vitality which has since enabled it to assimilate practically the whole outcome of German chemical activity. Of his own laboratory work, we had nothing from Meyer, for there was little or nothing a t the time to be told. He had entered the University in the autumn of 1865, when barely seventeen years of age, and apparently with no very definite conception of a career. Suddenly he elected to study chemistry, and attached himself to Bunsen with the idea of ultimately becoming a teacher. I t is not improbable that his choice was in a measure determined by the cir- cumstance that he had attended some of Hofmann’s lectures in Berlin in the preceding summer, and had thus been influenced by that great teacher, then in the fulness of his intellectual vigour.Those were the palmy days of Heidelberg-the days of Bunsen, Kopp, Kirchhoff, Helmholtz-and Meyer came under the spell of them all. His pro- gress as a student was exceptionally rapid, and the brilliant manner in which he gained his doctorate-without the adventitious aid of a thesis-strongly impressed the wholo philosophical faculty. Bunsen, especially, was greatly struck with the power and promise of the young Jew, then one of the youngest students in the University, and soon selected him as one of his assistants. It was in this capacity that I first made the acquaintance of Meyer. Bunsen for some years previously had been engaged in the examination of the mineral waters of South Germany, and Meyer a t the time I entered the Heidelberg laboratory was acting as water analyst.However great the disciplinary value of such work might be (and no one who has practised Bunsen’s method of water analysis, with its system of check and control, can doubt that it is one of the most rigorous quantitative exercises possible), I fear i t was not altogether con- genial to the active mind of the young assistant, who was yearning to try his ’prentice hand a t original research. Accordingly, towards tho end of 1868 he threw up the position, arid entered Baeyer’s little laboratory a t the Gewerbeakademie in Berlin. Although in a sense overshadowed by the more magnificently appointed University laboratories of Hofmann in the Georgenstrasse, and of Kekulb in Bonn, both a t that time comparatively new, the modest laboratory of the Gewerbeakademie, with its twenty workers, was already one of the most famous schools of organic chemistry in Europe.Baeyer himself had recently published his brilliant investigation of mellitic acid ; and Graebe, at first alone, and subsequently in conjunction with Liebermann and with Caro, was a t work on those remarkable sorim of inquiries which served to establish the true chemical nature and relationships of alizarin, and led eventually, with the independent collaboration of Perkin, to its artificial production on a commercial 0 2172 THORPE : VICTOR MEYER MEMORIAL LECTURE. scale. I well remember the interest and excitement which these dis- coveries created in Germany : they unquestionably gave an enormous impetus to the study of organic chemistry and attracted eager aspir- ants for chemical fame from all parts of the world, quickened, no doubt, by the perception of the rich promise of material benefit thus suddenly opened up.Heidelberg at that period was pre- eminently a school of inorganic chemistry : organic chemistry was represented by Delffs and was mainly studied by prospective apothe- caries. Erlenmeyer had been called to the Polytechnic at Munich, and the influence of KekulB’s teaching was as yet hardly felt by any of the Privat-docenten. Baeyer quickly recognised the power and ability of his pupil, and t o Baeyer was undoubtedly due the impulse which started him on his career.As a Vorgeruckter ” he attended no more lectures, and thus it happened that he who became one of the greatest organic chemists of his time never followed a course on organic chemistry. Shortly after his entrance into the laboratory, he began the series of half-dozen investigations which characterised his activity during his three years’ stay in Berlin. His first paper, published in the Berichte, was a note on the action of trimethylamine upon monochlorhydrin, which sub- stances form a basic condensation product, the chloride and the gold salt of which he described (Ber., 1869,2, 186). This was quickly followed by a short paper on diethyl thiodicarbonate, S(CO,Et),, which he obtained by the action of ethyl chloroformate upon sodium sulphide (Ber., 1869,2, 297).A far more ambitious production appeared in the following year, dealing with the constitution of the disubstituted benzenes (Annuden, 1870, 156, 265). I n this memoir, Meyer described a new method of introducing a carboxyl group into the molecule of aromatic compounds, no matter whether the substance already contained a carboxyl group or not. This was effected by the action of sodium formate upon the potassium salt of the aromatic sulpho-acid. Of the acids prepared synthetically by this method, isophthalic acid was the most important on theoretical grounds, as its production under these conditions led to a revision of the views then held with respect t o the orientation of the radicles in the “ortho” and “meta” (salicylic) series.Isophthalic acid had been shown by Baeyer to be a 1 : 3-derivative. “ Ortho ”-sulphobenzoic acid, obtained from benzoic acid, was thought t o have its radicles in contiguous positions. Meyer’s experiments showed that isophthalic acid was the only di- carboxylic acid formed from the sulpho-acid by interaction with a formate, whence he argued that ‘‘ ortho ”-sulphobenzoic acid, and the chloro-, bromo-, nitro-, amido-, and hy droxy-benzoic acids corre-THORPE : VICTOR MEYER MEMORIAL LECTURE, 173 aponding with it in constitution, must, like the isophthalic acid, be 1 : 3-derivatives. It followed that the meta ” (salicylic) series of compounds are the 1 : 2-compounds, The main facts of this paper have long since taken their place in the history of our knowledge of aromatic compounds, but the memoir has an especial interest as being Meyer’s first excursus into the realm of chemical theory.I n a subsequent extension of the work, in conjunction with Ador (Annuden, lS71, 159, l), he showed that in sulphanilic acid the substituent groups S@,H and NH, were in the 1 : 4 positions. The phenolsulphonic acid from sulphanilic acid he proved to be identical with Kekuld’s paraphenolsulphonic acid, and hence to have the position 1 : 4. Potassium monobromobenzoate fused with sodium formate yields isophthalic acid ; hence this bromobenzoic acid belongs t o the 1 : 3 series. At the conclusion of their memoir, the authors gave a list of the disubstituted derivatives of benzene then known, arranged in columns according to whether the second substi- tuent element or radicle is attached to the second, third, or fourth carbon atom, as deduced from the experimental evidence put forward.Their views as to the orientation of the substances there named, except in the case of the dihydroxybenzenes, have not been materially modified by subsequent inquiry, Pending the publication of this work, Meyer essayed to solve that cwcanurn of aromatic chemistry, the constitution of camphor (Ber., 1870,3, 116). He sought to show in the first place that camphoric acid is a dicarboxylic acid, C,H1,(CO,H),. Since camphor yields, by the action of dehydrants, an homologue of benzene, namely, cymene, he reasoned that it must contain the benzene nucleus, and hence the remaining four carbon atoms must exist in the side-chains.But by the oxidation of camphor to camphoric acid, the side-chains apparently are not attacked; the action would seem to be on two of the carbon atoms in the benzene ring. The carboxyl groups cannot be attached t o one and the same carbon atom, otherwise camphor would not yield an homologue of benzene by abstraction of water. therefore that, in all probability, camphor ought stitution expressed by one or other of the following (1) COHO C,H, 4: CH. (2) ?(OH) :C,H,,:QH. (3) YH:C,H,,:YH. 0- - It would follow to have the con- formulze : The first, or aldehydic, formula, suggested by Berthelot, was practically disproved by the work of Fittig and Tollens. The second formula, which contains the hydroxyl group, was rendered improbable by174 THORPE : VICTOR MEYER MEMORIAL LECTURE.Berthelot, and the improbability was further strengthened by Meyer, who found that acetic chloride was without action on camphor. The third formula then would seem of the three to be the most probable. The constitution of the group C8H,, can only be inferred from that of the camphor cymene. This, as shown by Fittig and his pupils, is probably for the most part methylpropylbenzene," Hence camphor would appear to have the constitution yH:C(CH,) * CH,*CH,* C(C,H,):CH, o------' and camphoric acid CO,H*Q(CH,)* CH,*CH,* 7(C,H7)*C0,H. Borneo1 would be CH(OH):C,H,,:CH,. These views have now only an historical interest. All that is certain in them is that Meyer's conception of camphoric acid as a dicarboxylic acid is correct. The work of Claisen and Manasse has rendered it practically certain, as long surmised, that camphor has the grouping C,Hl4<YH2, It has, co however, required the labour of a generation of workers, and the accumulation of a literature which, as regards its bulk, is without a parallel in any other department of chemistry, to unravel the true relations of camphoric acid to camphor, and hence to get an insight into the constitution of a substance which has been known in Europe and prized as a medicine since the twelfth century.Meyer acquired some experience in tuition, even in the early Heidelberg days, as a "coach," and in Berlin he added to his means, which were slender enough, by similar work. His success as a teacher induced Baeyer to recommend him to Fehling, who sought assistance, especially in modern organic chemistry and in laboratory teaching, in connection with his duties at the Stuttgart Polytech- nic.His departure from Berlin was a great loss to the little circle in the Gewerbeakademie, where his high spirits and geniality made him universally popular. He was an omnivorous reader and the power of his memory was astonishing, so much so that on his leaving, Baeyer exclaimed '( Jetzt werden wir ja wieder die Literatur nachschlagen mussen." How he came to leave it has already been told by Professor Liebermann. Johannes Wislicenus had just been called from the Zurich Polytechnic to Wiirzburg, and the President of the school, Kappeler, was engaged in searching for a successor. He came to Stuttgart and, unknown to * Widman (Bey., 1891, 24, 450) subsequently proved that cymene is methyliso- propylbenzene, but this does not affect Victor Meyer's argument, He remained in the Wiirtemberg capital barely a year.THORPE : VICTOR MEYER MEMORIAL LECTURE.175 Meyer, attended one of his lectures. Although Kappeler, as he him- self relates, knew little of chemistry, he was so struck with Meyer’s power of lucid and stimulating exposition that the decision to invite him to Zurich was immediately made. At the close of the lecture, he communicated tc the unsuspecting young teacher his idea, expressing, however, his fear that in comparison with his future students he might prove to be still too young. As Meyer laughingly promised to do his best, day by day, to repair this fault, the invitation was given, and thus, when barely 24 years of age, he found himself Ordinarius and Director of the chemical laboratory of the Zurich Polytechnic.The Zurich Polytechnic has enjoyed a succession of distinguished teachers, and Meyer worthily sustained and, indeed, greatly extended the fame of its chemical chair. He was now in possession of a well equipped laboratory and surrounded by eager, active students, stimu- lated and encouraged by the enthusiasm of a teacher as active and eager, and, it may be added, as high-spirited as themselves. The thirteen years of Meyer’s stay at Zurich constitute the most fruitful and the most brilliant period of his career : before its close, he had brought himself within the foremost rank of contemporary investi- gators. Some idea of his wonderful power of work, and of the stimulus he gave to others, may be gleaned from the fact that during that period the Zurich laboratory, under Meyer’s direction, gave close upon 130 papers and memoirs to chemical literature.It is, of course, impossible here t o do more than indicate, in the briefest possible out- line, the outcome and significance of the more important of them. During his short stay at Stuttgart he sent some half dozen papers to the Berichte, some of them in continuation of work which had occupied him in Berlin. The chief of these were put together in a memoir, in conjunction with Stuber, on the aromatic amines, which appeared in 18’43 (Annalen, 1873, 165, 161). The main objeet of the work was to gain further evidence in favour of Meyor’s view, that in the case of the chloro-, bromo-, iodo-, and nitro- derivatives of aromatic amines, obtained by direct substitution, it is always the hydrogen immediately contiguous to the amido-group which is replaced, or, in other words, that the NH, group exercises an attractive influence on the substituent.It was assumed byKekul8 that Riche and BBrard’s dibromaniline, obtained by the reduction of dibromonitrobenzene, was identical with the dibromaniline from acetanilide. Meyer and Stuber proved that such was not the case. It was found that Riche and B6rztrd’s dibromaniline yields, or is derived from, a l i p i d dibromobenzene, which boils at 219*4O, and remains liquid at -28’. Riese had previously obtained a liquid dibromobenzene boiling at 224O and crystallising below - lo.All the three possible dibrornobenzenes were thus made known. Meyer’s176 THORPE : VICTOR MEYER MEMORIAL LECTURE. surmise that the new dibromobenzene was the 1 : 3 variety has since been established, The authors also made known the existence of a new tribromobenzene melting at 119O, the symmetric or 1 : 3 : &derivative. The isomerism of the liquid dibromo benzenes was subsequently con- clusively demonstrated (Ber., 1874, 7, 1560) by the crystallographia examination of their mononitro-derivatives by Grot h and Bodewig. In this connection may be mentioned a short paper, in conjunction with Wurster, ‘‘ On some derivatives of solid Dibromobenzene ” (Annalen, 1874, 172, 57). In the attempt to prepare a nitrated phenylenediamine by acting upon di bromonitrobenzene with alcoholic ammonia, in the same manner that Walker and Zincke obtained nitraniline from monobromonitrobenzene, they found that only a moiety of the bromine could be displaced, the resultant product being a new substance, bromonitraniline, in which the NO, group is next to the NH, group, By converting this substance into bromo- phenylenediamine, the two NH, groups would be in close proximity ; on debrominating this compound, the resulting phenylenediamine was found to be identical with that discovered by Griess (m.p. 99O), whose surmise that the NH, groups were united to contiguous carbon atoms was confirmed. Meyer began also an inquiry on the chemical nature of chloral hydrate, a substance which, in consequence of Liebreich’s discovery of its anaesthetic action, had by that time become of considerable industrial importance, and was readily procurable.By the action of acetic chloride upon chloral hydrate, tetrachlorethyl acetate, CCl,*CHCl*O=CO*CH,, is obtained, identical with the product formed by the condensation of chloral and acetic chloride, or by the action of acetic chloride on acetaldehyde. Chloral alcoholate with acetic chloride yields C C 1 3 * C H < ~ ~ ~ ~ ~ c H l indicating that the alcoholate, as already shown by Henry on other chemical grounds, is the ethyl ether of trichlorethylidene glycol. By dissolving chloral hydrate in glacial acetic acid, Meyer obtained a white, crystalline substance, melting at BOO, which he regarded as isomeric with ordinary chloral hydrate (m. p. 55’). The chloral hydrates may have respectively the constitution (I) CCI,*COH + H,O.(2) CCl,*CH(OH),. It is not proved, however, that they are not polymeric (Annaten, 1874, 171, 66). It is possible that the substance thus obtained is identical with the uniaxial form observed by Pope which slowly changes into the biaxial modification stable at ordinary tempera- tures (Trans., 1899, 75, 458). Meyer does not definitelyTHORPE : VICTOR MEYER MEMORIAL LECTURE. 177 decide which of the two formula represents the constitution of ordinary chloral hydrate, but he inclines to regard it as trichlorethyl- idene glycol, which Perkin’s observations on its magnetic rotation definitely indicate that it is. Wallach’s observation of the conversion of chloral into dichloracetic acid was shown by Meyer to be in accordance with a general property of aldehydes in alkaline solutions to take up the elements of water, one molecule of aldehyde being thereby reduced, whilst another is oxidised.Meyer, in conjunction with his pupil Haffter, devised a very simple and rapid method of estimating the actual quantity of pure chloral in the commercial product, founded on the fact that chloral hydrate is rapidly decomposed by an aqueous solution of an alkali into chloroform and an alkaline forrnate (Ber., 1873, 6, 600). Although Meyer’s papers up to this time had amply demonstrated his power of investigation, and aEorded to critics like Kekuld and Baeyer abundant proof of the clearness and keenness of his vision, he had hitherto worked upon somewhat conventional lines.His memoir ‘( On the Nitro-compounds of the Fatty Series ” (Artmaten, 1874, 171, l), which appeared shortly after his removal from Stuttgart to Zurich, at once stamped him as an original investigator of a very high order. I n anticipation that two series of alkyl nitrites would be found to exist, denoted in hhe methyl series by CH,*NO, and CH,-O*NO, Meyer, whilst still at Stuttgart, had studied the action of amyl iodide upon silver nitrite and had obtained a colourless liquid, having the ordinary smell of amyl compounds, boiling between 150’ and 160°, which on analysis was found to have the composition C5H,,N0,. Hence it was isomeric with amyl nitrite, a yellow liquid of a peculiar, disagreeable smell, which boils a t 99”. To the new compound Meyer gave the name of nitropentane.The reaction was found t o be general. He now entered upon an elaborate investigation of the nitro-compounds of the alkyl series and their derivatives, and of questions incidental to the main subject, which, in conjunction with his pupils, among whom may be mentioned Stuber, Rilliet, Chojnacki, Wurster, Clonstam, Janny, Lecco, Locher, Tcherniac, Ceresolc, Niiller, Demuth, Keppler, and Zublin, continued to occupy him a t intervals for upwards of twenty years. One peculiarity which distinguishes aromatic from aliphatic com- pounds consists in the ease with which ‘nitration,’-that is, the replacement of hydrogen by the group NO, with the elimination of water-may be effected in the first-named substances. A reaction analogous to that by which nitrobenzene is formed from benzene was scarcely known among fatty compounds, the most familiar instance being the production of chloropicrin by the action of strong nitric178 THORPE : VICTOR MEYER MEMORIAL LECTURE.acid upon chloroform. The constitutional difference between the nitroparaffins, as the new group came to be called, and the alkyl nitrites consisted in the fact that, in the first-named substances, the NO, group is directly connected with a carbon atom, as in nitro- benzene, whereas in the alkyl nitrites the NO group is intermediately linked with the hydrocarbon radicle by means of oxygen. The alkyl nitrites are true esters capable of being resolved isto alcohols and nitrous acid by the hydrolytic action of alkalis or acids, The nitro- paraffins, on the other hand, are incapable of hydrolysis.By reduction, they yield alkyl hydroxylamines and then the corresponding amine. By reduction, however, the alkyl nitrites lose their nitrogen and form the corresponding alcohol. Heyer’s view that the nitroparaffins were veritable nitro-compounds mas not a t once accepted. Geuther, and subsequently Gotting, as- sumed that nitroethane was acetamidoxide, CH,*CO*NH,O, whilst Kissel regarded it as aeethydroxylamine, CH,*CO*NH(OH). It is true, as found by Meyer, that nitroethane, under the hydrolytic influence of strong acids, splits up into hydroxylamine and acetic acid, but since phosphoric chloride is without action upon nitroethane, an hydroxyl group must be assumed to be absent. As for Geuther’s view of the constitution of these substances, Meyer had little difficulty in showing that it wholly failed to explain all their known reactions.The general characteristics of the nitroparaffins, namely, the power of forming salts possessed by the primary and secondary compounds, the absence of this power in the tertiary series, together with the re- markable differences in the behaviour of bromine, and of the action of acids upon the primary and secondary nitroparaffins, were carefully studied by Meyer and his pupils. He found that when a solution of a primary nitroparaffin in potash is mixed with an alkaline nitrite and treated with sulphuric acid, the liquid acquires a blood-red colour which disappears on the further addition of acid. On shaking the whole with ether, there is obtained a solution of a new acid, known N* OH as a nitrolic acid, of the general formula C,R2n+~*C<No .case of nitroethane, the formation of the ethylnitrolic acid represented as follows : 2 I n the may be N* OH CH3*C<Eb + ON* OH E= H20 + CH,* C<NO, That such is the constitution of ethylnitrolic acid is indicated by its formation by the action of hydroxylarnine on dibromonitroethane, CH,. CeBr2 + H,N*OH = 2HBr + CH,. CcN0, N* OH . NO2 The nitrolic acids are colourless, sweet-tasting substances of a strongTHORPE : VICTOR MEYER MEMORIAL LECTURE. 179 acid reaction, readily soluble in water, and for the most part easily crystallisable. In alkaline solution, they give an intense blood-red coloration and form characteristic precipitates with salts of the heavy metals.They slowly decompose on standing, and on heating are quickly resolved into the corresponding fatty acid, nitrogen, and nitrogen dioxide. On treating the nitrolic acids with sodium amalgam, substances known as azaurolic acids are formed, They are strongly coloured, sparingly soluble substances, and differ from the corre- sponding nitrolic acid by containing two atoms of oxygen less. The best known member of the series is ethylttzaurolic acid, C,H,N,O, or more probably C,H,N,O,. On heating, it yields, together with forma- tion of nitrous oxide and water, ethylleucazone, C4HrN,0, a substance possessing both acid and basic properties, and in its general charac- teristics resembling an amido-acid. The secondary nitroparaffins, when treated with nascent nitrous acid, behave quite differently from the primary compounds.On adding sulphuric acid to the mixed solutions, a deep blue colour is produced and insoluble substances are formed, isomeric with the nitrolic acids, but which have no acid character. They were called by Meyer pseudo- nitroles, and have been regarded as nitrosonitro-compounds. ;g;>c<&@ Their formation may be thus represented (CH,),CH*NO, + OH*NO = 1T20 + (CH,),C(NO)*NO,, Scholl subsequently discovered that these substances may be obtained by the action of nitrogen peroxide upon the ketoximes: thus with acetoxime : 4(CH,),C:N*OH + 3N,04 -" 4(cH3)&<~0 + 2H,O + 2N0, a mode of formation which, as Meyer pointed out, indicated that they may be regarded as the nitrates of the oximes, (CH,),C:N-O*NO,.Their formation from the secondary nitro-compounds may be supposed to occur in the following phases : NO 2 (CH3),CH*N<? + HNO, = (CH,),CH*N<OH O*NO, , 0 (CH,),CH*N<ggo2 - H,O = (CH,),C:N*O*NO,. Meyer was inclined to give the preference t o the latter view of their constitution, as it is generally very doubtful whether compounds containing a nitroso-group (NO) directly linked to a carbon atom are capable of existence.180 THORPE : VICTOR MEYER MEMORIAL LECTURE, Tertiary nitro-compounds are unchanged by the action of nascent nitrous acid. Meyer pointed out how the characteristic colour reactions afforded by the behaviour of nitrous acid with the primary and secondary nitro- paraffins, and its inability to act upon the tertiary compounds, offered a ready means of distinguishing primary, secondary, and tertiary alcohol radicles.The iodido to be tested is distilled with silver nitrite, the distillate shaken with a solution of potassium nitrite in strong potash, diluted with water, and mixed drop by drop with dilute sulphuric acid. If the liquid acquires a red colour (formation of nitro- lic acid) which disappears with excess of acid and reappears on the addi- tion of alkali, we are dealing with a primary radicle : should the liquid give a blue colour (formation of pseudonitrole) soluble in chloroform, the compound is derived from a secondary alcohol radicle ; the non-forma- tion of colour indicates a tertiary radicle. The test ceases to be of much practical value beyond the 5 carbon series (compare Meyer and Jacobson, L e h h c h der Orgarkchen Chemie, 1893, 253, et seq.).The same line of inquiry was extended to the other main groups of aliphatic substances, and resulted in the discovery of new types of compounds. Thus, by the reduction of the isonitrosoketones and the isonitrosoacetoacetic esters, Meyer, in conjunction with Treadwell, obtained a series of volatile bases having apparently the generic formula C,H2, - 4N2, which they termed ketines and subsequently aldines. This group of substances is now generally known as the azines, and the substance first described by Meyer and Treadwell is dimethy lpyrazine, ,C(CH,): CH BCH,*CO*CH:N*OH + 6H = N ‘N + 4H,O. \CH :c~H,)/ Meyer had the faculty of keeping more irons hot a t a time than any man of his period.Although much of his thought and energy was directed in the first years of his sojourn in Zurich to the development of the new field of inquiry which his discovery of the nitroparaffins opened out, he continued his work on aromatic compounds, partly in defending positions he had already secured, and partly in breaking new ground. I n the latter connection, reference may be made to his discovery, with Michler, of diazoxybenzoic acid, and to the new class of azo-compounds which he described in conjunction with Ambuhl. A point of some little interest a t the time (1875) was his discovery that hydroxylamine and nitrous acid together yield nitrous oxide and water, NH,O + NO,H = 2H20 + N,O, in the same manner that nitrous acid and ammonia form nitrogen and water. The production of nitrous oxide by mixing together concentrated aqueous solutions ofTHORPE : VICTOR MEYER MEMORIAL LECTURE.181 hydroxylamine sulphate and sodium nitrite constitutes a noat and striking lecture experiment. He also showed, with Locher, that hydroxylamine may be obtained by a number of new reactions, as, for example, by acting on dinitropropane or ethylnitrolic acid with tin and dilute hydrochloric acid, when, in the one case, the amine is liberated in conjunction with acetone, and, in the other, together with acetic acid. (1) CH,. C(NO,),* CH, + 8H = CH,* Coo CH, + 2NH,O + H,O. (2) CH,. C(N*OH)*N02 + 4H + H2O = CH3* CO,H + 2NH3O. These reactions showed that the rule, hitherto regarded as universally true, that nascent hydrogen reduces nitroxyl to amidogen, has its exceptions.But perhaps the most important of Meyer’s discoveries a t this period was that of the oximes. He hadobserved that dibromonitroethane, under the action of hydroxylamine, passes into ethylnitrolic acid, and he antici- pated that the analogous nitrosoacetone would be formed in like manner from unsymmetrical dichloracet one. Experiment showed, however, that the chlorine in dichloracetone was replaced by a hydroxylamine rest, whilst the ketonic oxygen was replaced by the oximido-group, forming a compound termed by Meyer acetoximic acid, but now known as methylglyoxime, CH,. C(:N* OH)*UH(:N*OH). The fact that hydr- oxylamine would thus react upon carbonyl oxygen induced him, in conjunction with Janny, to study the action of this reagent upon ordinary ketones and aldehydes, and thus led to the discovery of the ketoximes and the aldoximes.This discovery has a two-fold signifi- cance. The reaction not only serves to indicate the existence of carbonyl oxygen in compounds, and hence is of value as a mode of determining constitutional problems, but it brought into existence a number of substances yielding derivatives of considerable interest. Further, it is not too much to say that the stereochemistry of nitrogen takes its rise from the discovery of the oximes. With Janny, he likewise obtained a-nitrosopropionic acid by the action of hydroxylamine on pyroracemic acid, a reaction which is almost quantitative and capable of being used as a test for pyro- racemic acid. Although it was quickly recognised as an exceedingly reactive substance, its use was greatly curtailed by the difficulty and expense of preparing it in quan- tity, Much of it, prior to 1883, was obtained by Dumreicher’s process, namely, by reducing ethyl nitrate by means of stannous chloride and hydrocliloric acid.Meyer showed how the irksomeness of the method, entailed by the necessity of removing the tin by sulphuretted hydrogen, and of dealing with the large volume of liquid produced, Lossen discovered hydroxylamine as far back as 1865.182 THORPE : VICTOR MEYER MEMORIAL LECTURE. might be materially lightened, and considerable quantities of hydroxyl- amine salts were made by the modified process in the Zurich laboratory. The position which hydroxylamine occupies between ammonia and nitric acid, which a t that time were held to be the main nitrogenous foods of plants, as well as its great; chemical activity when compared with the inertness of the other substances, seemed to Meyer to point to a possible formation of hydroxylamine within the plant, and to its playing an important part in the assimilation of starch and in the formation of albuminoids.In conjunction with Schulze, he therefore made comparative experiments on the action of hydroxylamine, ammoniacal salts, and nitrates upon plants, when it was quickly found that hydroxylamine acted as a poison to vegetable organisms. Meyer, however, points out that it may still be possible thah hydroxylamine may be formed in transition products, and yet act as a poison when taken up by the roots, just as peptone behaves as a poison when in- jected into the veins of animals.Reference may here be made to Meyer’s attempts to elucidate the constitution of ammonium salts. It was found that the di- methyldiethylammonium iodide, obtained by the action of ethyl iodide on dimethylamine, is identical with that produced by acting with methyl iodide on diethylamine, and no difference can be detected in the character of their salts. As the substances, although identical, were obtained by different reactions, it was inferred that they could not be ‘ molecular ’ compounds, that is, combinations of a tertiary base with an alkyl haloid, but must contain pentavalent nitrogen, whence, by analogy, ammonium chloride would be This assumption is only sound on the supposition that, in tho forma- tion of the salts, no change had taken place in the position of the alcohol radicles.The main conclusion would be invalidated if, for example, ethyl iodide, when reacting on trimethylamine, did not com- bine directly with it but was decomposed, as Lossen had suggested, as follows : N(CH,), + C,H$ = CH$ + N(CH3)2C2H5. To ascertain if such an interchange occurred, Meyer, in conjunction with Lecco (~nnahn, 1876, 180, 173), studied the action of ethyl iodide upon tetramethylammonium iodide. If Lossen’s contention were sound, the reaction should be N(CH3),$ + C,H,I = CH31 + N(CH,),C,H,I.THORPE : VICTOR MEYER MEMORIAL LECTURE. 183 No action, however, was found t o occur either with ethyl or methyl iodide alone at any temperature up to 180”, or in presence of methyl alcohol or water.Ladenburg and Struve tested Meyer’s conclusion by making similar experiments with benzyl iodide and triethyl- amine, and with ethyl iodide and benzyldiethylamine, and were dis- posed to regard the resultant compounds as isomeric, although closely alike in most of their properties. On repeating the observations, Meyer found that no difference existed ; the substances prepared in the two ways were absolutely identical. Suggestive and fruitful in ideas as Meyer was, he was seldom at a loss in devising means t o put them to the test of trial. I n many of his mental characteristics not unlike Davy, as an experimentalist, he had all Davy’s resourcefulness with far more than his patience. As I knew him i n Heidelberg, he was an excellent manipulator ; still his temperament would never have permitted him to better the example of the great master under whom he was trained.We could all look on and marvel at the patient, concentrated power with which Bunsen would devise, elaborate, and perfect some new form of apparatus, or some new method of analysis. The first steps were very simple-so simple indeed that it was frequently impossible to divine their ultimate purpose. It was from such small beginnings that we obtained the whole process of gasometric analysis, the burner, the photometer, the various voltaic batteries, the spectroscope, the filter-pump, the ice-calorimeter, the flame reactions, &c. Before Bunsen gave a piece of apparatus t o the chemical world, he left it practically perfect ; the striving after perfection was a veritable passion with him, and numerous were the forms or modifications through which the apparatus or the method passed before he rested satisfied with it.Although bleyer’s genius was of a different order, the influence of the Heidelberg training is to be recognised in the various forms of laboratory apparatus with which his name is connected. Chief among these are his modes of determining vapour densities. The elegant modification of Gay Lussac’s method intro- duced by Hofmann left nothing to be desired in the case of compara- tively volatile substances unacted upon by mercury, but many bodies were known, and their number was being rapidly increased, in which this method was inapplicable. Meyer accordingly, in 1876, devised his displacement method (Ber., 1876, 9, 1216).This in principle was similar to the method suggested by W. Marshall Watts as far back as 1867, from which it differed in that Wood’s metal-an alloy of bismuth, lead, tin, and cadmium, melting below 70°-replaced the mercury, and that the volatilisation was effected at the temperature of boiling sulphur, that is, at 444’. This process allowed of the determination of the vapour density of many substances which could184 THORPE : VICTOR MEYER MEMORIAL LECTURE, be vaporised at temperatures below the boiling point of sulphur, and compounds like diphenyl, methylanthracene, triphenylamine, paradi- bromobenzene, and paradiphenylbenzene, had their vapour densities ascertained for the first time by means of it, The method was further modified in the following year (Ber., 1877, 10, 2068), mercury being used instead of Wood’s metal and the vapours of boiling water, aniline, ethyl or amyl benzoate or diphenyl- amine-depending on the temperature required-were employed tts a bath instead of sulphur vapour.The t6 Luftverdrangung Methode ”-the simple and extremely con- venient process-which will for all time be associated with the name of Victor Meyer, was devised in 1877 (Bey., 1877, 11, 1867). The apparatus is now one of the commonest articles of laboratory furniture, and i t is not too much to say that, thanks to the ease with which the whole operation may be carried out, more vapour densities have been determined by its aid than by any other means. The apparatus is usually constructed of glasg, but by making it of glazed porcelain, determinations can be effected a t very high tempera- tures.Except for special reasons, neither the temperature of the heated bulb nor its volume need be known : all that is required is that the temperature should be sufficiently high to gasify the substance under examination. Avariety of liquids-water, xylene, aniline, ethyl benzoate, amyl benzoate, diphenylamine-depending on the temperature needed t o effect complete vaporisation, may be used as media for heating the bulb. For temperatures exceeding 300°, a bath of molten lead may be employed, the glass bulb of the apparatus being coated, as suggested by Watson Smith and Davis, with a moderately thick film of soot before immersion in the bath so as to diminish the risk of fracture.Mr. Watson Smith, who was with Meyer at Zurich, and who has kindly sent me some reminiscences of him a t this period, writes: “It was somewhat singular that just as Victor Meyer, with Carl Meyer (no relation), had completed their vapour density apparatus for bodies of very high boiling point, I had just obtained in the pure state specimens of the three isomeric dinaphthyls, all of which urgently awaited the determination of their vapour densities. They mere the first new high boiling substances with which the apparatus and method were tried. Victor Meyer was immensely pleased and interested with this circumstance, and we practically all three worked the de- termination together, the results amply proving the reliability and accuracy of the new method. Of course in these cases the lead bath was used ” (compare Trans., 1879, 35, 226 ; 1880, 3’7, 491).The molecular weights of a number of substances were quickly ascertained by this method, for example, phosphorus pentasulphide, indium chloride, cuprous chloride, stannous chloride, arsenious oxide,THORPE : VICTOR MEYER MEMORIAL LECTURE. 185 antimonous oxide, cadmium bromide, &c. Volatilised in an at mo- sphere of hydrogen chloride, ferrous chloride yielded values between FeCI, and Fe2Cl,. Ferric chloride a t no temperature showed a vapour density corresponding with Fe,Cl,, whilst a t 750” and 1077”, its mole- cule would seem to be FeC1,. Potassium iodide at 1320’ in an atmo- sphere of nitrogen had a density corresponding with KI. Arsenic and phosphorus at a white heat had densities approaching the values for As, and P,, whilst zinc a t 1400°, and bismuth at 1700”, were found to be monatomic, and thallium at 1700” diatomic.In 1879, the two Meyers, Victor and Carl, astonished the chemical world by announcing (Bey., 1879, 12, l426), as the result of de- terminations of their vapour densities a t high temperatures, that the halogens were capable of undergoing dissociation or possibly decom- position. As regards chlorine, this announcement at once threatened to re-open a question which had been regarded by most people as practically settled since July 12th, 1810, when Davy read to the Royal Society his classical memoir on oxymuriatic acid. Davy, it is true, had never stated that chlorine was an element i n the absolute sense of that term.What he inferred was that it was a substance which ‘‘ has not as yet been decompounded,” and therefore is “ ele- mentary as far as our knowledge extends.” The very name chlorine, which he suggested, inculcated this view, “ To call a body which is not known t o contain oxygen and which cannot contain muriatic acid, oxymuriatic acid, is contrary to the principles of that nomen- clature in which it is adopted. . . , After consulting some of themost eminent philosophers in this country, it has been judged most proper to suggest a name founded upon one of its obvious and characteristic properties-its colour, and to call it chlorine, or chloric gas. Should it hereafter be discovered to be compound, and even to contain oxygen, this name can imply no error, and cannot necessarily require a change.” Had chlorine then been ‘decompounded’? Did it contain oxygen? Were Berzelius and Murray right after all? Was there such an entity as murium? The pages of the popular scientific periodicals of the time show how these questions agitated the minds of chemists.The indications of the spectroscope were advanced as confirmatory of Meyer’s results, and there was much exercise of ‘ the intelligent anticipation of events before they occur ’ which occasioned him some annoyance at the time. However sanguine he might be that he had decomposed chlorine, and however freely he might talk with his colleagues, he never committed himself in print to any statement of the kind. To begin with, the amount of oxygen he had obtained was very small, and there was uncertainty as t o the action of the chlorine upon the silica or alumina of the VOL.LXXVII. P186 THORPE : VICTOR MEYER MEMORIAL LECTURE. porcelain at the high temperature, and whether the materials em- ployed were wholly free from moisture. I have it, on the authority of Professor Lunge, whose knowledge was derived from daily inter- course with him, that Meyer himself refused to consider the fact as es- tablishad until he had worked in an apparatus made of material devoid of oxygen, and to this end he obtained a special grant from the Zurich authorities to defray the cost of a vessel of platinum; Meanwhile Meyer’s observations on chlorine were repeated, and their validityimpugned by Crsf ts (Compt. vend., 1880,90,153 et sea.) who found, by a modification of Meyer’s method, that the gas, even at the highest temperature of the Perrot furnace, showed no change indica- tive of diseociation or decomposition.Meyer, in conjunction with Ziiblin, at once repeated Crafts’ determinations on preformed chlorine and confirmed their accuracy. As regards bromine and iodine, however, the observers were in substantial agreement. Thus with iodine : Victor Meyer. Crafts and Meier. Temp. Density. D’lD. Temp. Density. 0’10. 450° 8.85 - 445O 8.74 - 686 8-72 0.99 830--880 8’07 0-92 842 6.76 0’77 1020-1050 7.01 0 ‘80 1030 5.75 0.66 1275 6-82 0.66 1670 5.70 0.65 1390 5.28 0.60 Naumann showed from these results, on the assumption that the molecule I, splits up into two atoms 191, that the course of the dissociation is in accordance with the result required by the mechanical theory of gases, namely, that the increments of decomposition corre aponding to equal differences of temperature increase gradually from the temperature at which dissociation begins up to that at which 60 per cent.of the vapour is decomposed, and then decrease in a similar manner up to that temperature at which dissociation is complete, In conjunction with Lnnger, Meyer greatly extended these observa- tions, and subsequently published them as a monograph, entitled ‘‘ Pyre chemische Untersuchungen ” (Braunschweig : Vieweg u. Sohn, 1885). As regards bromine, they found that the gas, when sufficiently diluted with air, had a normal density, namely, 5 5 2 even at the ordinary temperature, and no sensible change occurred up to 900° even when diluted with eleven times its volume of nitrogen.At 1200°, the density had diminished to 4.3 on dilution with five volumes of nitrogen, At a white heat, the density of the diluted bromine fell to 3.6. Experiments at higher temperatures were not possible,THORPE : VICTOR MEYER MEMORIAL LECTURE. 187 as at above 1600' the platinum apparatus is rapidly attacked by both bromine and chlorine. The alteration in density of bromine vapour a t high temperatures has recently been studied by Dr. Perman and Mr. Atkinson, who have found that no sensible diminution occurs up to about 750" a t atmospheric pressure, at which point dissociation becomes just ap- ppeciable, especially at low pressures, and gradually increases with increasing temperature (Proc.Roy. Xoc., 1900, 66, 10). In the case of chlorine, it was found by Meyer and Langer that no analogous change occurred below 1200°, no matter whether pure or highly diluted chlorine was employed, At 1 400', however, the density of the diluted chlorine fell from the normal value 2.45 to 2.08. Similar observations with carbon monoxide seemed to show that at 1690' this gas is partially decomposed into carbon dioxide and carbon, 2CO = C -I- CO,. Carbon dioxide itself experiences no change in density at this temperature in a platinum apparatus, although when passed through a porcelain tube filled with broken pieces of porcelain it undergoes dissociation, as already shown by Deville. This pheno- menon may be connected with the remarkable observation of Menschutkin and Konowaloff that dissociable vapours are far more rapidly broken up in presence of asbestos, or pieces of glass, or even of the roughened sides of glass, than when the interior of the glass vessel is perfectly smooth.Nitrous oxide, heated in a porcelain tube, is entirely resolved into oxygen and nitrogen a t goo', and in a platinum tube at 1690'. Nitric oxide remains unchanged up to 1200'; at 1690', it is com- pletely decomposed into its elements. Hydrogen chloride also appears to be partially, whilst sulphuretted hydrogen is entirely, decomposed at the latter temperature. Cyanogen has a normal density up to 800" ; at 1 ZOO', it suffers decomposition. Meyer made his pyrochemical investigations under very unfavour- able conditions, The magnificent chemical institution which Zurich now possesses was not then built, The old laboratory was a low building to the east of the main block of the Polytechnicum, and the only room which could be spared for the purpoge was so small that, in spite of the best ventilation possible, +he temperature not unfrequently rose to 50'.Moreover, both he and hi3 assistants suffered greatly from the strenuous ardour with which the wotk was carried on, and he himself eventually broke down under the strain of it. I saw him in Zurich in the autumn of this year (lS79), and was surprised and shocked to notice, although it was at the endof the vacation, how nervous and jaded he seemed. I believe the distressing insomnia from which he suffered at times throughout the rest of his life began at about this period.I n reference t o this time, Mr. Watson Smith writes : Meyer had a most excitable P 2188 TRORPE : VICTOR MEYER MEMORIAL LECTURE. mind and was a tremendous worker. His assistant, Carl Meyer, told me that on several occasions he was so overworked, not by compulsion, but through the mere influence of Meyer’s presence, his mental power, and enthusiasm, that he came very near committing suicide during the fits of depression following exhaustion after long-continued spells of work.” Pyrochemical problems continued to interest Meyer to the end, and he was quick t o take advantage of any hint which seemed t o promise the possibility of their solution. I n a lecture before the Nntur- forscher Versammlung in Heidelberg, he regretted that the lack of vessels of sufliciently refractory material prevented him from working at the higher limits of temperature even then attainable.‘‘ There can be no doubt,” he said, ‘‘ that new and undreamt-of discoveries will manifest themselves-that a new chemistry will disclose itself, when we are furnished with vessels that will enable us to work a t tempera- tures at which water can no longer exist, and at which oxy-hydrogen gas becomes an uninflammable mixture.” Shortly before his death, he returned to the subject with new appar- atus made of a platinum-iridium alloy capable of withstanding a far higher temperature than pure platinum, and he was in hopesof being able to construct vessels of magnesia which would allow of the application of temperatures over 2000O.Meyer, at the time he announced his discovery of the dissociation of the halogens, was thirty-one pears of age. He was now on the flood- tide of his prosperity. His published work had shown him to be an investigator of uncommon power and originality, and students flocked to him from all parts, to participate in the pioneering work which his astonishing energy and enthusiasm opened out. In its triumphs it was indeed a time of “joyous yesterdays and confident to- morrows.” He was happily married to the friend of his youth, Fraulein Hedwig Davidson, whose ‘ Verlobungstag ’ was the very day on which he received his call to Zurich. What she was to Meyer only those who were privileged to know his home circle can fully realise. Meyer’s first great grief came to him with the death of his eldest daughter, and in 1882 he lost his friend Wilhelm Weith, Professor of Chemistry in the University.How close and intimate was their friend- ship was evident to all who frequented the meetings of the Zurich Chemische Gesellschaft, where the two professors were generally to be found seated side by side at the head of the table; it is reflected too in the obituary notice of his colleague which Meyer wrote for the Berichts. In the autumn of 1882, Meyer was requested to undertake the delivery of the series of University lectures on benzene derivativesTHORPE : VICTOR MEYER MEMORIAL LECTURE. 189 which had been interrupted by Weith’s death. I have already attempted to indicate what Meyer was as a teacher. No one could possibly take greater pains in the preparation of his lectures, or study more to make them instructive and interesting. It is generally supposed that organic chemistry does not lend itself to effective lecture illustration.“I well recollect,” writes Mr. Watson Smith, ‘‘ that the word most fre- quently used in Zurich in defining the opinions of Victor Meyer’s students of his lectures was ‘ brilliant I ’ ” Another of our Fellows, Mr. John I. Watts, who attended his course in 1879-80, writes :- Such was not the case when Meyer had to teach it. (‘What particularly struck me about his lectures was their finished style. He made fairly constant use of notes, speaking with great rapidity. Yet his treatment of the subject was very clear, and his language perfect. The experiments were always well prepared and exceptionally suocessful.Indeed, his lectures were most popular, and both at his work and outside the Polxtechnic there was no professor who was inore respected and admired by all students than Victor Meyer. Young, handsome, well-dressed-for a German professor, with a quick wit and a genial manner, he was a welcome addition to any gathering. When, in 1881, he had a ‘ call ’ to Aachen and elected to remain at Ziirich, the students treated him to a torchlight pro- cession and a grand ‘ Kommers.’ Meyer watched the ‘ Fackelzug’ of over 1000 students from a balcony, and later, sitting as the honoured guest in a still greater throng, he seemed indeed a happy man.’’ Si>milar testimony is given by Dr. Sudborough, who was with him in Heidelberg, and who writes :- “As a lecturer, Meyer was clear, concise, and extremely lucid, and his delivery was easy and natural. His lectures were given by the aid of care- fully written notes, and were fully illustrated by experiments, the table being always crowded with apparatus both in the organic and inorganic lectures.It was very rare indeed for an experiment to fail ; this was firstly due to Meyer‘s own dexterity as a manipulator, and also to the care which wag bestowed upon the preparation of the experiments.” It was in the course of these lectures on benzene derivatives that Meyer came upon what is perhaps the most brilliant of all his dis- coveries-that of thiophen. How he lighted upon it is well known, but the story bears repetition. He desired to show his class the SO.called indopheain reaction of Baeyer, a t that time held to be indicative of benzene, but to his astonishment not a trace of the characteristiu blue colour made its appearance, although, as was his wont, he had rehearsed the experiment just prior to the lecture, It appeared that his assistant, Sandmeyer-himself one of Meyer’s ‘discoveries’-had handed to him a sample of the benzene made in the lecture course by heating benzoic acid with lime, and a t once drew his attention to the fact that the rehearsal had been made with the ordinary laboratory supply-190 THORPE : VICTOR MEYER MEMORIAL LECTURE. the Benxot prissim. crystallisaturn of the dealers, and, of course, derived from coal-tar. Meyer, at the moment, was so fully occupied t h a t he might well have put aside the incident, or have given no immediate heed t o its significance.But that was not his way. Fortune scatters her chances indifferently, and every man may have his share, but it is not given to each t o perceive when he is favoured, or to know when to grasp (4 the skirts of happy chance.” Madame de Wtael once said that a most interesting book might be written on the important consequences which spring from little differences, and it was the little difference that riveted itself on Meyer’s mind. H e at once began the investigation of the cause. All kinds of benzene to be found in Zurich were tested, and it was soon definitely established that it was only coal-tar benzene that gave the indophenin reao- tion. Meyer’s first idea was that it might be ocuasioned by an isomeric-a second benzene found in coal-tar, Within less than a month he had -ascertained that the reaction was due t o some sulphuretted product accompanying coal-tar benzene, and that Baeyer’s indophenin was probably a sulphur compound.Meyer’s action was characteristic of him. Before communicating with Baeyer, he carefully repeated his experiments, and only when all ground for doubt was removed did he inform his friend of his obser- vations and of the inferences he had formed. Baeyer at once sent him a specimen of his indophenin, and the fact that it actually was a sulphuretted compound mas then established. Meyer found that coal-tar benzene, after repeated shaking with oil of vitriol, no longer reacted with isatin, and hence he determined t o search among the sulphonic acids so formed for the reactive substance.By distilling the product obtained by shaking 10 litres of benzene with oil of vitriol, he obtained a few cubic centimetres of a clear, thin, mobile liquid containing sulphur, which boiled at about 83a and remained liquid in a freezing mixture of ice and salt. It gave a most intense reaction for indophenin. The amount of the new substance present i n coal-tar benzene was very small, a t most not more than 0.5 per cent. Thanks to the co-operation of his friends, Messrs. Bindschedler, Busch and Go., of Basle, he was enabled to repeat this experiment on a large scale, as much as 250 litres of coal-tar benzene being operated upon at a time, and the sylphonic acids converted into the lead salts, which were then mixed with sal ammoninc and distilled.The crude produot, which contained about 28 per cent. of sulphur, was found t o react strongly with bromine, forming a heavy, colourless, highly refractive liquid, boiling a t 2 1 lo, greatly resembling dibromobenzene, but showing on analysis the composition C,H,Br,B The new com- pound was the dibromo-substitution product of a substance whichTHORPE : VICTOR MEYER MEMORIAL LECTURE. 191 Meyer was at first inclined to call thianthren, then thiophan, next thiol, and lastly thiophen, to denote that it was a sulphur-containing substance giving derivatives analogous to those of phenyl. I n the early part of the following June, that is, within about six months of his first observation, he had obtained a considerable quantity of thiophen, and was in a position t o show to the Swiss Naturforscher Versammlung, which met during that summer in Zurich, that its chemistry was hardly less extensive than that of benzene itself.Thus it was that a chance observation-the observation of a little difference-added a new section to organic chemistry. It would be quite impossible within the limits at my disposal to show how this section was developed by Meyer and his pupils. In 1888, he published, in the form of a monograph, dedicated to his friend and patron, President Kappeler, (‘ dem hochherzigen Forderer wissenschaftlicher Bestrebungen,” an account of its condition at that time (Die Thiophengruppe. Braunschweig : Vieweg u. Sohn), from which it appears that during the preceding five years no fewer than 106 contributions t o its history had been made from his own labora- tory, and some 40 from those of others.How fertile the field still continues may be gleaned from the circumstance that upwards of 50 papers on the same subject have since made their appearance in various journale. Meyer’s restless energy had now begun to read most seriously upon his general health. At times he was almost prostrated by nervous exhaustion ; he had frequent spells of insomnia, and his friends viewed with alarm the signs of physical decay which now set in, in spite of the occasional holidays, mainly among the Alps, which he gave himself. In 1884, he again broke down, and although at the moment he was im- mersed, with his colleague Lunge, in the plans for the new chemical laboratory of the Polytechnic in which, as he states, he had hoped ultimately to resume his pgrochemical labours under more favourable conditions, he was obliged to relinquish, for a time, all idea of work, and towards the end of the year was ordered away to the Riviera, where he wintered.I n the following spring, he received a ‘call’ to Gattingen as the successor of Hubner. This he eventually decided to accept, and entered upon his duties there in the summer session of 1885. He was not able, as he had hoped, to take leave of his Zurich students at the time, but what they thought of him-with what affection and respect he was regarded-was seen in the terms of the Address they sent to him on the occasion of his opening lecture at Gottingen. It was seen, too, in the way he was received by them during a visit t o Ziirich some months later, on the occasion of the seventieth birthday of his friend Kappeler.Professor Goldschmidt,192 THORPE : VICTOR MEYER MEMORIAL LECTURE. who was present, thus describes the sceno : ‘( I see him even now before me as he spoke t o the students at the ‘ Kommers’ in the evening. The ‘Ziircher Polytechnikers’ have, as a rule, but little opportunity of knowing the professors outside their special faculty, and have, therefore, but little interest in those who are not their own teachers. As Victor Meyer’s slender form appeared on the platform, and as his bright blue eyes glanced round the assembly, there broke forth a shout of welcome from all-engineers, machinists, architects, as well as from his old students the chemists-to beended in a whirl- wind of applause a t the close of a speech, sparkling and witty as ever.’ ’ With renewed health and vigour, he now set about the plans for the new laboratory which the authorities had decreed should adorn the ‘ Georgia-Augusta,’ for Wohler’s old place no longer sufiiced to con- tain the chemical workers which Gottingen had now to receive. Whilst it was being erected, he continued his pyrochemical work, and his investigation of the thiophen derivatives, and began with Paul Jacobson the admirable “Text-book of Organic Chemistry,” which, in the critical selection and arrangement of its material, is still unsur- passed. With Auwers, he resumed the study of benzil and its derivatives which he had begun with Wittenberg and Goldschmidt. With Miinchmeyer, he began the study of the behaviour of phenylhydrazine towards various groups of oxygen compounds, and he sent a short paper t o the Bsrichte on thiodiglgcol compounds, and on an easy method of preparing /3-iod opropionic acid from glycerol.With Demuth, he undertook the investigation of the sulphuranes, a group of disulphides of the general formula C,H,*S*C,H,* SR. Other papers were on the densityof nitric oxide, which showed no evidence of asso- ciation or molecular duplication even at - looo; on isophthalaldehyde ; on the negative nature of the phenyl group; and on isodibromo- succinic acid. It was characteristic of his receptivity that Meyer should be among the earliest workers in Germany to perceive the value of Raoult’s method of ascertaining molecular weights; it was first used in the Gottingen laboratory to determine the molecular weight of some derivatives of benzil which yielded two series of isomeric compounds, both series having the same constitution, in the ordinary sense, but which were yet distinct from one another and yielded different derivatives. Other papers of this period were on the thio-derivatives of deoxy- benzoin and its analogues (desaurins), and, with Riecke, on the carbon atom and valency. The latter paper is of interest as an example of Meyer’s (‘ scientific use of the imagination,” and mayTHORPE : VICTOR MEYER MEMORIAL LECTURE, 193 be studied in connection with an earlier paper in 1876 (AmmaZen, 1876, 180, 192) on the same subject, as showing how he grafted the theoretical conceptions of van’t Hoff upon the teaching of KekulB.According to Meyer, the carbon atom is surrounded by an ethereal shell which, in the case of an isolated atom, has a spherical form ; the atom itself is the carrier of the specific affinities, the surface of the shell is the seat of the valencies ; each affinity is determined by the existence of two opposite electrical poles, which are situated a t the end-points of ft straight line small in comparison with the diameter of the ethereal shell. Such a system of two electric poles is called a double- or di-pole. The four valencies of a carbon atom would be re- presented by four such di-poles, the middle points of which are situated on the surface of the ethereal shell, but freely movable within it.The di-poles themselves can rotate freely round their middle point. The carbon atom has a greater attraction for positive than for negative electricity, and the positive pole of a valency is slightly stronger than the negative pole. This hypothesis explains why the four valencies take up the position of a regular tetrahedron ; why they can be diverted from this position ; why the valencies of one and the same carbon atom cannot combine together, whilst the valencies of different carbon atoms can do so ; why there are two kinds of single-binding, one stable, and the other allowing free rotation; and lastly, why free rotation ceases in cases of double- or treble-binding (Be?., 1888, 21, 946 ; compare Abstr., 1888, 549). Stereochemical questions-we owe the phrase to Meyer-were indeed at this time occupying much of his thought.In a paper with Auwers (Be?., 1885, 21, 784), he pointed out that the existence of the two isomeric dioximes of beazil, discovered by him in conjunction with Goldschmidt, would, if for both the formula C,H,*C(N*OH)* C(N*OH)-C,H, were established, be in direct contradiction to the hypothesis of van% Hoff that two carbon atoms united by a single affinity are free to rotate, the axis of rotation being the bond of union, and that isomerism is only possible for those substances of the type EC-C!, which cannot, by rotation round the common axis, be converted into the same form. The two dioximes were carefully compared as regards their melting points, solubilities in water, alcohol, ether, or acetic acid, and the conditions under which the a-form is converted into the P-modification were ascertained.To further remove all doubt as to the possibility of merely physical isomerism, and to prove that the oximes are not only different from one another, but yield different derivatives reconvertible into their respective oximes, the propionic and isobutyric derivatives were prepared and compared. The result showed that the dioximes were of identical chemical oompasition, and194 THORPE : VICTOR MEYER MEMORIAL LECTURE. hence it appeared that van’t Hoff’s hypothesis must be so altered as to admit of cases in which free rotation round the axis cannot take plaoe, as otherwise no explanation of the isomerism of the a- and P-dioximes is possible (compare Abstr., 1888, 597).He subsequently showed how the work of Bethmann, Graebe, and Baeyer confirmed these views. Wislicenus’ theory as to the free rota- tion of singly-bound carbon atoms would appear to be limited to certain cases ; absolutely free rotation is probably possible only when the substituting atoms or groups are identical ; where, as is the case in the majority of compounds, the atoms or groups are not identical, there will be some definite position of equilibrium ; only in cases where the substituting atoms or groups are equally negative will there be several positions of equilibrium (Bey., 1890, 23, 2079 ; Abstr., 1890, 1083). Meyer’s perspicacity and critical insight are well illustrated in a lecture which he gave to the German Chemical Society in 1890 ‘( On the Results and Aims of Stereochemical Research.” It is of interest to the student as giving a fairly complete historical account of the development of space formulze, and more especially for its criticism of the work of Baeyer and Wislicenus on the stereochemical formule of single-, double-, and treble-linked carbon compounds, and of the stereo - chemical conceptions of Hantzsch and Werner in the case of nitrogen compounds.With regard to the assumption that the nitrogen atom may be represented as a tetrahedron, and that the isomerism of the benz- aldoximes may be similar to that of fumaric and maleic acids, it is pointed out that the structure of the oximes is in all probability not identical, Two isomeric forms of each of the unsymmetrical oximes of the formula OH-N:CXI’ are indicated by the hypothesis of Hantzsch and Werner, but they do not appear to exist.If the tetrahedral representation of the nitrogen atom were tenable, we should have to assume that substituted ammonias can exist in the isomerio forms N-a /= and N l ? , but such bodies are not known. 1 6 \a We must therefore assume that in ammonia the hydrogen atoms are placed symmetrically with regard to the nitrogen atom, and this can only find expression in a plane formula (Ber., 1890, 23, 567 ; compare Abstr., 1890, 719). Reference may be made here to the short paper on isomeric oximes of unsymmetrical ketones and the configuration of hydroxylamine, in conjunction with Auwers (Bar., 1890, 23, 2403), in which the authors advance further evidence that the isomerism of the oximes cannot depend upon structural dissimilarity, but must be sought for in theTHORPE : VICTOR MEYER MEMORIAL LECTURE.I95 nature of the hydroxyIamine group. Assuming the correctness of the theories of van’t Hoe and Wislicenus regarding the arrangement of atoms in space, the combined effect of the attraction of the nitrogen and oxygen on the hydroxylic hydrogen of hydroxylamine would cause it to be in a plane dieerent from that occupied by theremaining atoms in the molecule. This hypothesis suffices to explain all observed facts : unsymmetrical oximes would therefore exist in two forms, C:N*6 and a R b c1 C:N*?. b H Werner is shown by the two formulae, The difference between this theory and that of Hantzsch and QH C:N and H C:N--b (Hantzsch and Werner). (humers and Meyer).The formation of an oxime by the action of nitrous acid is readily accounted for on the graund that i t is a substituted hydroxylamine; morwver, the fact that no case of geometrical isomerism has ever been observed in the azo-, azoxy-, and imido-compounds tells in favour of this theory (compare Abstr., 1890, 1263). To this period belongs also the work on the azines ; on deoxybenzoin ; on the aromatic nitriles; on tetramethylsuccinic acid; and on the oximes of phenanthrsquinone. Meyer was not destined t o remain long in Gdttingen. The new laboratory was barely finished, when, in 1889, he received a 6 call ’ to Heidelberg. Bunsen, full of years as of honours-the Nestor of Chemistry, as his friends were wont to call him-had expressed a wish to retire, and of all his many students there was none, he said, whom he wished more to take his place than he who, twenty-one years before, had vorked with him in the modest little room of some four or five places, which had constituted his private laboratory.To Heidelberg accordingly Meyer vent, with the coveted title of Geheimrath, and the promise of a new and enlarged laboratory. Although only forty years of age, he was now, so far as worldly position was concerned, a t the summit of his career ; he had returned to his Alma Mater and the rest of his days were to be given to her service. During his four years’ stay in Gdttingen he had in great measure recovered hiB health and with it the elasticity of his active, buoyant temperament.I saw him in Heidelberg in the spring of 1891, when he was busy with the enlargement of the old laboratory, and it was196 THORPE : VICTOR MEYER MEMORIAL LECTURE, with a glance of pride-a pardonable pride-that he pointed out the places where he and I had worked with ‘ Papa ’ Bunsen, ‘ So kindly modest, all accomplished, wise,’ in the corner place near the window, towering above both of us. It was strange, too, to hear the sound of children’s voices and their laughter; and the bustlo of servants in what were formerly the silent, half-deserted rooms overlooking the Wrede-platz ; and stranger still to me was it, as we together called upon Bunsen, sitting solitarily in his rooms overlooking the Bunsen-strasse, t o behold the meeting and to listen to the greeting of these two men-the memory of whose names and fame Heidelberg will cherish so long as Heidelberg exists, To all of us life has its dramas, and in some of these the incidents are as moving as those ever conjured up by playwright or poet.How well I remember it ! He was as bright, as active, as mentally vigorous as of old, although i t was but too obvious that his physical strength was not the equal of his nervous energy. Meyer’s earliest experimental work at Heidelberg was mainly concerned with the continuation of investigations begun a t Gattingen. But he was perpetually breaking new ground or seeking to clear up doubtful points in ground already partially explored. The classical labours of Frankland on zinc ethyl might be thought to have definitely established the chemistry of that substance, but even on such a comparatively simple matter as the action of oxygen on zinc ethyl there was room for still further inquiry.The white compound obtained by Frankland, as the result of the oxidation of zinc ethyl, was regarded by him as a mixture of zinc oxide, ethoxide, and acetate. It was found, however, by Meyer and Demuth to con- tain no acetate, but to be mainly composed of a peroxide, ZnEt*O*OEt, as proved by its power of liberating iodine from potassium iodide. The explosive character of the substance is thus explained. Zinc ethouide, in fact, does not appear to have been prepared (Ber., 1890, 23, 394). In conjunction with a number of his pupils-Krause, Freyer, Askenasy, and others-Meyer in 1891 began the investigation of 8 subject already associated with the name of his predecessor, namely, on the conditions determining both the gradual and the explosive combustion of gaseous mixtures, Although a considerable amount of experimental work was done, the results obtained, ourious and interesting as they were in some particulars, led to no very definite general conclusions.It was found that the temperature at which combination occurred This wits the last occasion on which I saw Meyer.THORPE : VICTOR MEYER MEMORIAL LECTURE. 197 varied with the nature of the vessel, and depended upon whether the gases were confined or not. Ignition takes place at a lower tempera- ture when the mixture is in a closed vessel than when passing freely through an open tube. If, however, an open vessel containing the mixture is heated suddenly, explosion takes place at the lower temperature.I n the cases of gradual union, no relation between time and amount of combination could be perceived. As showing the influence of the nature of the surface, it was found that, when the bulbs were silvered inside, the union of oxygen and hydrogen was rapidly effected at a temperature of about 200°, whereas in an un- silvered bulb the gaseous mixture had to be heated to above 530' before any sensible amount of water was produced, The principal quantitative results are embodied in the following table in which tlie mixture did not explode a t the lower temperature in each column, but did so at the higher : Equivalent mixtures. Free current. Hydrogen, oxygen .................. 650--730° Methane, oxygen ..................650-730 Ethane, oxygen ..................... 606-650 Ethylene, oxygen .................. 606-650 Carbon monoxide, oxygen ......... 650-730 Hydrogen sulphide, oxygen ...... 315-320 Hydrogen, chlorine .................. 430-440 Closed bulbs. 530-606' 606-650 530-606 530-606 650-730 250-270 240-270 I n a subsequent paper with Munch (Ber., 1893, 26, 2421), the temperatures of explosion of gaseous mixtures were determined by placing the vessel containing the gases inside the bulb of an air thermometer immersed in a metal bath. The mixture of a gas with the amount of oxygen theoretically necessary for its complete com- bustion was passed through a 6ne tube to the bottom of the internal vessel, and lighted as it issued from the mouth of the exit tube.At a certain temperature, the flame ran down the tube and the con- tents of the vessel exploded. This temperature-the temperature of explosion-was determined by displacing the air contained in the air thermometer by means of hydrogen chloride, collecting it over water, and measuring it. I n 38 experiments with a mixture of hydrogen and oxygen (pure electrolytic gas), the temperature of explosion varied from 620' to 680°, being about 650' in mean, The tempera- ture is not affected by variations in the rapidity with which the gaseous mixture enters the glass vessel, or by the presence of frag- ments of glass or sand. I n presence of platinum, the gases com- bine quietly, and if the glass vessel is very small no explosion occurs. The temperatures of explosion of a number of aliphatic hydro-198 THORPE : VICTOR MEYER MEMORIAL LECTURE.carbons, mixed with equivalent amounts of oxygen, were then determined as follows : Methane ...... 656-678O Propane . , , , , . 545-548 Ethane ...... 605 - 622 Propylene ... 497-5 1 1 'Ethylene ...... 5'77-590 isoButane , . . 545-550 Acetylene ... 509-515 isoButylene , . . 537-548 Coal-gas with 3 times its volume of oxygen ... 647-649 It would thus appear that the temperature of explosion falls as the number of the carbon atoms in the molecule increases; that it is probably lower for ppimary than for corresponding secondary hydro- carbons ; and is less for hydrocarbons containing a double bond than for those containing only single bonds, and still less for those containing a triple bond (compare Abstr., 1894, ii, 11).Mention may here be made of the work done, in conjunction with Bodenstein, on the decomposition of gaseous hydrogen iodide by heat, This gas was selected for the reason that the action of heat upon it is reversible, and hence it might be expected that the establishment of a condition of equilibrium will be in no way influenced by the many disturbing circumstances which were found to occur in the case of other gaseous mixtures. Combination of hydrogen and iodine vapour takes place even at 444' (b. p. of sulphur), and the hydrogen iodide formed is far more stable, at all events in the dark, than has hitherto been supposed. It is, however, very sensitive to light, In bulbs which were exposed for 10 days to direct sunshine, 59 per cent. of the gas was decomposed, and when exposed throughout the summer, practically the whole of the gas is resolved into its constituents.Experiments on the relation of the amount of decomposition to temperature gave the following results i Relative amount of HI decomposed, as determined Temperature of boiling By decomposition. By direct union. Sulphur ............ 444' 0.2150 0.2104 Retene ............... 394 0.1957 4 Mercury ............ 350 041731 0,1738 At 310' (b, p. of diphenylamine) the relative amount of HI decoma posed was 0.1669, instead of 0.1550 as calculated from the above numbers. The difference between the observed and calculated result8 is due to the circumstance that the heat of formation of hydrogeh iodide is, at ordinary temperatures, negative ( - 1600°, Thomsen), but from the fact that the decomposition at temperatures such as 350-444' increases with rising temperatures, it follows from van't Hoff's prin- ciple (Principe de l'equilibre mobile) that the heat of formation at theseTHORPE : VICTOR MEYER MEMORIAL LECTURE.199 temperatures is positive. There must, therefore, be a temperature at which the heat of formation is zero, and at which also the decom- position is at a minimum, This point, as the experiments show, lies between 310' and 350°, and calculation by van't Hoff's formula showed t h a t it is at 324'. As it was found that two bulbs heated under the same conditions always gave the same result, it was possible to study the decomposition as a time reaction, and by the formula given by Nernst.The constancy in the values actually obtained for each of the foregoing temperatures showed that, in the case of the decom- position af hydrogen iodide by heat, the change occurs in a perfectly regular manner ( B e y . , 1893, 26, 1146 ; compare Abstr., 1893, ii, 369). This short account of Meyer's labours in physical chemistry may conclude with a brief reference t o the determinations of the fusing pointn of salts melting only at relatively high temperatures, which he made in concert with his pupils. These he was able t o obtain by the aid of the platinum air-thermometer he described in conjunction with Freyer. The following is a list of his final values : Sodium chloride ...... 816' Sodium bromide.. . . , . 757 Sodium iodide ......661 Potassium chloride., . 800 Potassium bromide.. . 722 Potassium iodide ... 684 Potassium carbonate 878 Sodium carbonate ... 849 Sodium biborate ... . . , 878' Sodium sulphate . , . . . 863 Potassium sulphate 1078 Caesium iodide .".... 621 Calcium chloride ... 806 Strontium chloride.. . 833 Barium chloride.. . . . . 92 1 Rubidium iodide ... 641 (Compare Heycock and Neville, Trans,, 1895, 67, 190). In 1892, Meyer and Wachter made known the possibility of the existence of a class of aromatic derivatives, known as the iodoso- compounds, in which the monovalent group I0 replaces hydrogen. The first representative of the series was iodosobenzoic acid, C,H510,, which they obtained by the action of fuming nitric acid or a boiling and acidified solution of potassium permanganate upon orthoiodo- benzoic acid.It is a crystalline, solid substance, melting a t about 200°, sparingly soluble in water or ether. It liberates iodine from potassium iodide, and chlorine from hydrochloric acid, forming orthoiodobenzoic acid. It is an extremely feeble acid, and its silver salt when dry is highly explosive. No iodoso-derivatives could be obtained from meta- or para-iodo- benzoic acida. Of the two iodoparatoluic acids, the one in which the iodine atom occupies the ortho-position t o the carboxyl group yields an iodoso-derivative similar t o iodosobenzoic acid, but the200 THORPE : VICTOR MEYER MEMORIAL LECTURE. isomeric acid does not yield a corresponding compound, If, however, paraiodobenzoic acid be previously nitrated, it may be converted by the further action of fuming nitric acid into an iodoso-derivative, 10*C6H,(N02)*C02H.In like manner, the iodoparatoluic acid may be made t o yield an iodoso-compound by previous nitration (Ber., 1893,26, 1354). By the further action of oxygen on an alkaline solution of iodoso- benzoic acid, iodoxybenzoic acid, I0,*C6H,*C02H, is formed, a white, crystalline substance, turning red on exposure to light, and decom- posing with explosion at 233'. It is a much stronger acid than the iodoso-derivative, forms moderately stable salts, and gives character- istic colour reactions with aniline and phenol (Ber., 1893, 26, 1727 ; compare Abstr., 1893, i, 577). Hartmann and Meyer found that when iodosobenzene, C6H,*I0, is dissolved in strong sulphuric acid, the solution, on dilution with water, yields the sulphate of a base, phenyliodophenyliodoniurn hydroxide, I-C,H, ' ~ ~ 5 > 1 -OH.A similar change occurs with paraiodosotoluene. The free bases have a strong alkaline reaction, and form characteristic crystalline salts. Meyer was thus led to the discovery of a remarkable group of substances known as the iodonium compounds, the simplest aromatic representative of which is diphenyliodonium hydroxide, /%H5- I-C,H,. \OH. These bases are compounds in which two of the valencies of the iodine atom are satisfisd by aromatic radicles whilst the third is satisfied in the free base by hydroxyl, and in the salts by an acid radicle. The iodonium bases are readily soluble in water, are strongly alkaline, and in their behaviour, as in that of their salts, show a remarkable similarity with the derivatives of silver, lead, and, more particularly, thallium, These bases are formed by the decomposition of the iodoso- and iodo-hydrocarbons under various conditions ; for ex- ample, by the action of moist silver oxide upon an intimate mixture of equivalent proportions of iodosobenzene and iodoxybenzene, O H C6H5*I0 + I02*C6H, + AgOH = C6H,*I<C + AgIO,.6 5 By the addition of potassium iodide to the aqueous solution, diphenyl- iodonium iodide is precipitated. This compound stands i n the same relation to iodobenzene that trimethylsulphonium iodide does toTHORPE : VICTOR MEYER MEMORIAL LECTURE. 201 methyl sulphide, and as tetramethylammonium iodide does to tri- methylamine. It cry stallises from alcohol in long, pale yellow needles, and decomposes on heating almost quantitatively into iodobenzene, c,,H,,T, = ~c,H,I.If the decomposition is started at one point, it proceeds through tho whole mass with development of heat. The existence of these remarkable bases and salts, which recall the sulphonium-, ammonium-, arsonium-compounds, &c., shows that a complex which is composed of one iodine atom and two molecules of phenyl, that is, of constituents which are otherwise negative, possesses strongly basic properties, From the general behaviour o? the iodonium compounds, it is evident that the complex -I<C6H5 or C6H5 in general -I<;, (where R and R, are aromatic radicles) possesses I the function of a metal analogous to thallium (compare Lehrbuch der Organischen, Chsmie, Meyer and Jacobson, 2, 127).It is interesting to note that the physiological action of the diphenyliodonium chloride resembles that of ammonium salts on the one hand, and of heavy metals, such as lead and thallium, on the other. Doses of 0*02-0*03 gram produce total paralysis in frogs, both the motor nerve-ending and the muscle substance being affected, A dose of 0.08 per kilo, proves fatal to rabbits, the spinal chord and medulla oblongata being also affected. A study of the condition8 determining the formation and hydrolysis of ethereal salts of aromatic acids occupied Meyer, in conjunction with his pupils, and more especially Sudborough, from 1894 up to the year of his death. It was found that benzoic acid and its substituted pro- ducts, as a rule, readily yield practically the theoretical quantity of an ethereal salt when treated with methyl alcohol and hydrochloric acid in the cold.On the other hand, the symmetrical trisubstitution pro- ducts of benzoic acid yield no ethereal salts whatever under these conditions. This rule holds absolutely for all 1 : 3 : 5-trisubstitution derivatives of benzoic acid (Me, NO,, C1, Br, I, and CO,H), except those containing one or more hydroxyl groups. The same is true of all substituted benzoic acids in which the 2 : 6-hydrogen atoms (C0,H = I) have been replaced by other atoms or groups. The acids which do not yield ethereal salts when treated with alcohol and hydrochloric acid can readily be converted into these substances by the action of methyl iodide on their silver salts, or of methyl alaohol on the acid chlorides.This remarkable difference in behaviour may be ascribed t o a gtereo- chemical cause, the substituent groups being supposed to hinder the VOL. LXXVII, Q202 THORPE : VICTOR MEYER MEMORIAL LECTURZ. introduction of the alkyl group to such an extent that under the prescribed conditions the reaction does not proceed." Acids in which the carboxyl group is linked with the benzene nucleus by one or more carbon atoms readily undergo etherification. The constitution of a substituted benzoic acid may, therefore, be ascertained in this way, and the method may also be used for isolating or purifying those acids which will not undergo etherification. The nitrophthalic acids behave similarly : dinitrophthalic acid [NO, : C0,H : C0,H : NO, = 1 : 2 : 3 : 41 gives no ethereal salt, whilst the acid [NO, : CO,H : CO,H : NO, = 1 : 3 : 4 : 51 yields monalkyl salts.1 : 2 : 6-Dinitrobenzoic acid gives no ethereal salt (Abstr., 1895, i, 93). Chloronitrobenzoic acid [CO,H : NO, : C1= 1 : 2 : 61 yields no ethereal salt, showing that the rule applies when the substituents are dissimilar. Diortho-substituted benzoic acids are not etherified at low temperatures when one of the substituents is hydroxyl. Meyer was of opinion that etherification, in the case of analogous compounds, is diversely influenced by substituents of different relative mass. He imagined that those radicles which prevent etherification at high temperatures have a much agreater relative mass than those which only hinder it at low temperatures, but it is probable that the methyl group and its normal homologues will produce almost identical effects, since the action is chiefly due to that carbon atom which is directly linked to the benzene nucleus.According to theory, those ethereal salts which are formed with greatest difficulty should be hydrolysed least readily, and such Meyer found to be generally the case.? These conclusions have been tested by Kellas (Zeit. phys. Chern., 189'7, 24, 221), who has measured the velocity of etherification for a large number of monosubstitution derivatives of benzoic acid. From a study of the influence of temperature, and of the nature of the substituent, he has more precisely indicated the limits within which they may be regarded as generally true, Considerations of space preclude more than a bare reference to the work on the derivatives of ethyl dinitrophenylacetate; on the in- doxazen group ; on the laws of substitution in the aliphatic series ; on the synthesis of triphenylacrylonitrile and on the isomerides of tri- phenylacrylic acid ; on the modes of introduction of acetyl groups into aromatic hydrocarbons ; on the substitution of the hydrogen * This supposition has been modified by Wegscheider, who introduces Henry's conception of the formation of an additive compound between the alcohol and the acid.According to Wegscheider, the ortho-substituents prevent the formation of such additive compounds (compare, however, Davis, Trans., 1900, 77, 33). t This is approximately true for the benzoic series of acids,1 but does not obtain for the acetic and probably other series (compare Sudborough and Lloyd, Trans., 1899, 75, 467).THORPE : VICTOR MEYER MEMORIAL LECTURE.203 in trinitrobenzene by alkaline metals j on the fusibility of platinum ; on the formation of tetriodoethylene from diiodoacetylene ; on the durenecarboxylic acids ; on the action of potassium permanganate on hydrogen, methane, and carbon monoxide ; on the slow oxidation of hydrogen and carbon ; on the evolution of oxygen during reduction ; on hexahydrobenzophenone and its oximes ; and on diphenylamine from orthobromobenzoic acid. Meyer contributed to the literature of chemistry, either alone or in conjunction with his pupils, upwards of 300 memoirs and papers. No account of Meyer’s scientific activity would be complete with- out some allusion to the various pieces of apparatus with which he enriched operative chemistry. Reference has already been made t o his methods of determining vnpour density, and to his mode of ascertaining the melting points of substances fusible only at high temperatures.H e also greatly improved the methods of accurately determining the solubilities of substances a t various temperatures. His form of water-bath is to be met with in many modern laboratories, surmounted, it may be, with the funnel-shaped cover which he devised to prevent access of dust to the evaporating liquid. Particularly neat and convenient are the drying ovens he constructed in which constant temperatures are obtained by means of liquids of different boiling points, for example, toluene, xylene, anisoil, &c.Analytical chemistry had little attraction for Meyer, and, beyond his mode of diagnosing primary, secondary, and tertiary alcohols and alcoholic radicles by colour reactions (see p. 180); and the method he devised, with Jannasch, for the simultaneous determination of carbon, hydrogen, and nitrogen in the elementary analysis of organic substances, he made no contribution to this department of the science. As the director of a large chemical laboratory, and as a laboratory teacher, Meyer worthily followed in the footsteps of Bunsen. In proof of this, I may here quote the testimony of some of our Fellows who have worked under him. Mr. John I. Watts thus refers to him in the Zurich days : ‘‘ Victor Meyer as a teacher had a wonderful faculty of infusing enthusiasm into his students.He was constantly in the laboratory, and whether the pupil was engaged upon the analysis of some simple, well-known substance, or was pursuing oziginal investigation, he seemed somehow to succeed in making him feel how interesting was his work. Possessed of a very quick and active intelligence, he would point out the reason of the difficulties almost before the student had finished recounting them. He was himself a constant worker, and when engagedin his work he always appeared to be in a high state of pleasurable excitement.” LJimilar testimony is afforded by English chemists who were with him at Heidelberg. Dr. J. T, Hewitt writes : Q 2204 THORPE : VICTOR MEYER MEMORIAL LECTURE.“ Professor Meyer was universally liked by the men who had the privilege of working under him. He had an extraordinary capacity for hard work, and his example, together with the interest he took in his men, induced in them a more or less similar love of work. After the morning lecture, which in the summer semester was at eight, he would come round the lriboratory and see how every one was getting on, though of course he spent more time with those who were doing joint work with him than with those who were working with the other professors. We used very often to see him again during the moriiing, and at least once in the afternoon. I n 1891, when I first went to Heidelberg, the most important work being done was on the slow combustion of electrolytic gas, and, not only those who were actually working on this subject, but every one else in the laboratory; used to take great interest in what was going on.Meyer’s way of taking up old pieces of his work again and again meant that a very varied sort of work was clone in the laboratory ; for example, in consequence of Nef s criticism, nitro-fatty compounds were again examined, the result on the students being excellent, in that their general interest in chemistry was aroused. Meyer, as you well know, was an excellent speaker, not only in the lecture room, but in taking the chair at meetings of the Heidelberger Chemische Gesellschaft, when he was seen to great advantage.” Dr. Sudborough, who served him as an assistant when in Heidelberg, writes : ‘‘ As organiser and director of the laboratories, Meyer undoubtedly exhibited great business qualities, and everything worked extremely smoothly, owing probably to the fact that his staff had been with him for a number of years and were all on intimate terms of friendship with him, During the time I was an assistant, I had opportunities of observing with what care he entered into even the minutest financial details in connection with the department.I‘ In the laboratories he was extremely genial and pleasant, always having a kindly word for the students, and taking a great interest in their work. Characteristic, too, was the hopeful way in which he alwayslooked forward to the successful termination of each piece of work, and by this means endeavoured to keep up the interest of the student.Every student who worked under him respected and honoured him as a scientific leader of the first rank, but in addition they felt a deep friendliness towards him on account of the kindly interest he took in them and in their work. A goodly percentage of those carrying out ‘ Arbeits ’ under him were either English or American ; in fact, Meyer appears to have had a predilection for English and American students. ‘‘ Mention must also be made of Meyer’s connection with the Heidelberg Chemical Society, of which he was an ardent supporter-in fact, may be said to have been its soul : he and Bernthsen (of the Badische Anilin- u. Soda-Fabrik) were the two presidents in my time and both were frequent contributors.” Dr, Jocelyn F. Thorpe writes : (6 Perhaps that which impressed one most about Victor Meyer, besides his power and ability as an exponent and lecturer, was the faculty he possessed of conferring some of his enthusiasm upon the students who worked under him, Be his interest ever so slight and his knowledge of the subject ever 80 small,THORPE : VICTOR MEYER MEMORIAL LECTURE.205 no student could work long with Victor Meyer without feeling that he had a part in a system ; that he was, in fact, one of the instruments by which the plans and ideas of a master mind were being shaped. Noticeable, too, was his wonderful power of grasping and remembering every little detail of the re- searches upon which he was at the moment engaged. At times, as many as thirty men would be working under him on subjects widely varying in character, yet in no case would he forget what each individual had been doing when he last visited him ; occasionally he would astonish the student by aaking him what had become of some (by the student) long-forgotten snb- stance, the properties of which he could remember most distinctly.“ Every morning after his lecture he would enter the laboratories and personally not only visit the students who were working directly under him, but also those who were engaged in research with the other Professors and Privat-docenten of the department. ‘‘ Not only will Victor Meyer live inithe memory of those who worked under him as a leader in chemistry, but many will remember him as the genial and kindly host. On many evenings during the semester he would give either supper parties or small dances, and occasionally a ball, t o which his students were welcomed, and when his camaraderie and great tact were especially noticeable to those of us who, being foreigners newly arrived, were unacquainted with the language and social customs of his country, I remember meet- ing him inHeidelberg the year before his death and asking him something, I cannot now remember what, bnt at any rate he was unable to answer me a t the time, and asked me to call and see hin; the next day.He, however, stopped and tied a knot on his pocket handkerchief, saying, with a sad smile, ‘ my memory is not what it was.”’ “ Towards the last his wonderful memory began to fail, Meyer’s literary ability, combined with his power of lucid exposi- tion, made him an admirable writer of what are called popular science articles. He was a frequent contributor t o t h e Natu~- wissenschaftlichen Rundschau, and a number of his essays appeared under the title of (‘ B u s Natur und Wissenschaft ” (Heidelberg, 1892). His love of natural scenery and his power of graphically describing it may be seen in his “Marztage in Kanarischen Archipel ’’ (Leipzig, 1893), a record of travel, written during tho enforced rest following upon one of his too frequent periods of nervous prostration. One who had studied him carefully and knew him well t h u s writes of his personal qualities and of the influence and attraotion he exerted upon all who came in contact with him : ‘‘ Victor Meyer had 8 remarkable power over men. Where he entered, there he soon becsine the centre ; each one listened to him, all collected round him. I n the fascination he exercised there was nothing intentional or self-conscious ; it was far lesg the influence of a commanding strength than the working of an incomparably attractive and many-sided nature. To this, too, his appearance contributed : the finely chiselled head with the splendid blue eyes might, at first sight, betoken the artist, were it not that there was in the expressive206 THORPE : VICTOR MEYER MEMORIAL hECTUSE, features a rare blending of the lively temperament with the contemplative calm of the philosopher. “ In the circle of his fellows he captivated all by the eagerness with which he followed anything new, discussing and elucidating it in a manner peculiarly his own ; by the joyous, often enthusiastic, recognition of other men’s work, and by the warm-hearted interest he displayed in the scientific struggles of his juniors. In society, he showed himself an accomplished convei3sationalist and raconteur, an intelligent and warmly appreciative connoisseur of the arts of music and literature. As a host, he studied the comfort of every guest in his house. At the ‘ Biertisch his sunny humour and overflowing wit diffused a general harmony ; and his enthusiastic love of natural scenery made him the most delightful of travelling companions.” (Paul Jacobson, in Ntrtuywiss. Rundschau, 12, 43 and 44, p. 19). Meyer’s merits were recognised in every land where science is cultivated. He was a corresponding member of the Academies of Munich, Berlin, Upsala, and Gottingen, and an honorary member of many learned societies. The University of Konigsberg made him an Honorary Doctor of Medicine. The Royal Society gave him the Davy Medal in 1891. H e was elected an Honorary Foreign Member of our Society in 1883, and attended the celebration of our Jubilee in the spring of 1891. Many of our Fellows will no doubt recall the rstirring speech, instinct with a true eloquence, which he made at the banquet in responding t o the toast of ‘( Our Foreign Members,” with its striking peroration :-‘‘ Moge die Chemical Society, neben allen ihren anderen schonen Aufgaben auch in Zukunft ihre volkerverbindenden Ziele in so erfolgreicher Weise anstreben wie bisher, m6ge Sie bluhen und gedeihen als eine Pflegstatte der Wissenschaft, f u r ihr Vaterland vorerst, aber nicht minder fur alle Volker welche sich im friedlichen Wettbewerb wissenschaftlicher Arbeit verbundet wissen.” May the Chemical Society, in the years t o come, continue, as in the past, to recognise, with a full and generous appreciation, the work of those across the seas who engage with us in the friendly rivalry oE scientific labour ! And may our action i n thus recording the services in our own annals of the gifted man whose May this aspiration be fulfilled! prosperous labour fills The lips of inen with honest praise,’’ tend i n some degree, however small, t o that consummation for which he so earnestly and so eloquently pleaded 1