The COUPER QUEST e
Narrative Compiled by
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LEONARD DOBBIN* This article describes the steps in the course of an en- remained unrecognized until long after his death. The p i r y carried out at the instance of Professor Richard prosecution of the enquiry to its eventual complete success Anschatz of Bonn University, to trace the ancestry and v ~ c salmost entirely the work of the late Professor Crum relatives of Archibald Scott Couper, a Scots chemist Brown, of Edinburgh University, to whose assiduity whose researches on the quadrivalence of carbon and the and persistence the clearing away ofthe obscurity that had linking of carbon atoms in organic compounds, simul- for decades surrou@ed Couper's disappearance from the tuneous with and independent of the work of Kekuld, domain of chemiGal investigation was chiefy due.
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T IS the purpose of the following sketch to describe the steps in the course of an enqui~ycarried out at the instance of Professor Richard Anschiitz of Bonn University, to trace the ancestry and relatives of Archibald Scott Couper. The prosecution of the enquiry to its eventual complete success was almost entirely the work of the late Professor C ~ u mBrown, whose instrumentality in the matter has in some instances been less fully acknowledged than it deserved to be, and to whose assiduity and persistence the clearing away of the obscurity that had for decades surrounded Couper's disappearance from the domain of chemical investigation was chiefly due. Incidentally the causes will be indicated which awakened the desire of Anschutz to obtain a knowledge of Couper that the histories of chemistry and works on chemical biography did not supply. Shortly after the death of Emeritus-Professor Crum Brown, the writer enquired from his representatives whether there were among his possessions any letters, papers, portraits, or other material that might possess special interest from the viewpoint of chemical history. In response there were handed to him a considerable number of photographs and other portraits, letters from various chemists, and also a dispatch box labeled "Archibald Scott Couper." This box contained the correspondence, notes, photographs, proofs, etc., connected with the "Quest" carried out by Crum Brown in 1906 and with the publication of the paper on Couper's "Lie and Chemical Work" that Anschutz communicated later to the Royal Society of Edmburgh [Proc. Roy. Sac. Edin., 29, 193-273 (1909)l. Having been associated with Crum Brown in the capacity of Grst assistant during the period of his experiences in catlying on his enquiries and having been in almost daily conversation with him concerning their progress, the writer became familiar with most of the details connected with them and was probably more
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Formerly Reader in Chemistry, University of Edinburgh; Secretary of the Alembic Club, Chemistry Dept.. King's Buildings, Edinburgh.
fully acquainted with these than any other person outside his own immediate circle. When the contents of the dispatch box were examined, it was found that it would be possible to construct an authentic and nearly complete account of the successive steps in the enquiry, and the matter seemed to be of sufficient interest to justify the placing of the facts on record in connected form. The paper by Anschutz already mentioned should be read in conjunction with this sketch.t It includes considerable detail relating to Couper's life, together with a critical examination of his published papers. A few short extracts from the paper are quoted in an appendix to the following sketch. By one of those chances that are occasionally met with, the name of Couper as a writer on chemical subjects presented itself about the year 1893and again some twenty years later--on each occasion in a different connection and in each connection in an arresting manner-to Dr. Richard Anschiitz, then professor of chemistry in the University of Bonn. At the earlier date mentioned, Anschiitz, in conjunction with one of his students, George Dunning Moore, carried out an investigation on the action of phosphorus pentachloride on salicylic acid.' This was by no means a new subject of research. The interaction had been examined by Chiozza in 1852,2also by Gerhardt3 and his pupil Drion4; and further, a t a considerably later date, by KekulPand by Kolbe and L a u t e m a ~ nas , ~ well as by Couper.' There was a gaod
t Anschiitz published a German version of his paper in the Archzv fiir die Geschuhtt der Naturwissaschafkn und der Tecknik. 1, 21961 (1909). MOORE, Ann., 228, 308 (1885). Cxrozzn, Comfit. rend., 34, 850 (1852); Ann. chim. phyhys.. 131. 36, 102 (1852); Ann., 83, 317 1852) GE-or, Comfit.rend., 38,32 t1854); Ann., 89,360 (1854). ' DRION, Compt. rend., 39, 122 (1854); 46, 1238 (1858); Ann., 92, 313 (1854); 109, 373 1859) b K ~ ~ Ann., ~ ~ 105, h , 286 11858); 117, 145 (1861); BuU. Aced. Roy. Belg., [2], 10, 337 (1860). 'KOLBEAND LAUTEMANN. Ann.. 115, 157 (1860). COUPER. Compt. rend., 46, 1107 (1858); Edin. New Philos. J.. IN. S.1, 8, 213 (1858).
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deal of variation in the results reported by these several experimenters, but it was the work of Conper that attracted the particular attention of Anschiitz, inasmuch as Couper had obtained from the reaction mixture by distillation and had described and analyzed a liquid product that contained large proportions of phosphorus (about 12%) and of chlorine (about 38'%). This liquid he called "terchlorophosphate of salicyl" and formulated i t (C = 6 and 0 = 8) ClrHnCl8POs. This compound was obtained whether Couper operated
Anschutz, repeating Couper's experiments and submitting the reaction products to rapid distillation under greatly reduced pressure, was able to confirm completely the results that Couper had announced and to show why, in all probability, others had failed whereas Couper succeeded, although Couper distilled under ordinary atmospheric pressure. It is outside the purpose of this narrative to enter into the details connected with this matter. It may suffice, therefore, to note that Couper's work and name were introduced to the notice of ~- Anschiitz in an intimate manner a t the time, but i t does not appear that any special interest in his personality was aroused a t this earlier date. The second occasion on which Couper's name and work presented themselves conspicuously to Anschutz was in connection with the preparation of a comprehensive biography of Kekul6 which Anschiitz, his pupil, who had succeeded him in the Chair of Chemistry a t Bonn, had been invited to write. The following is a brief outline of the relevant facts. On March 16, 1858, Kekul6 sent in, from Heidelberg, to the editors of Liebig's Annalen his famous paper "On the Constitution and the Metmorphoses of Chemical Compounds and on the Chemical Nature of Carbon," in which paper he drew attention, as new ideas, (1) to the quadrivalent character of the carbon atom, and (2) to the linking of carbon atoms. The first of these ideas he had somewhat casually referred to in a footnote to a paper that he had published in the preceding year, but without elaborating the idea. In the later paper Kekul6 proceeded from this idea to the suggestion of methane as an additional "type" in the sense in which that word was understood in Gerhardt's theory of types, to which he was a 6tm adherent. By a remarkable coincidence, Couper a t the very same time submitted to Wurtz. in whose laboratorv. ,. in Paris, he was a student, for presentation to the French Academy of Sciences, a paper entitled "On a New Chemical Theory," in which he likewise developed both of these ideas and remarked about the second of them that so far as he was aware the idea that, as he put it, carbon "enters into chemical union with itself" was there "signalised for the first time." Couper's paper was written from a standpoint of complete opposition to Gerhardt's type theory, which he treated with a certain degree of sarcasm. Unfortunately for Couper, Wurtz, who was not himself a member of the Academy, had to get the paper presented by a member, and seems to have been dilatory in doing so, with the result that Couper's paper was not read until June 14, 1858, whereas Kekule's appeared in the part of Liebig's Annalen issued on May 19th, preceding. Needless to say, this was highly mortifying to Couper, and it led to an unpleasant incident between h i and Wurtz, as will appear later. Kekul6 died on July 13, 1896. Some time thereafter, Anschutz was occupied with a study of papers by Kekult5 and contemporaries, in connection with the biography of Kekul6 that he was compiling, and in ~
OF ARCHIBALDSCOTT COUPGR PORTRAIT
Taken in Paris in 1857 or 1858.
upon salicylic acid itself or upon its methyl ester, the main constituent of oil of wintergreen. The other experimenters mentioned failed to obtain this phosphorus and chlorine derivative and thus threw doubt upon the accuracy of Couper's work. They concluded that the reaction led to the formation of products that did not contain phosphorus and were merely chlorine derivatives of salicylic acid. These conclusions were arrived a t without almost any support from analytical determinations, and the fact was left unexplained that, during the vigorous action that occurred when the phosphorus pentachloride was mixed with the salicylic acid or its methyl ester, little or no phosphorus oxychloride was given off, but only hydrochloric acid, or, in the case of the methyl ester, a mixture of hydrochloric acid with methyl chloride.
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doing this he found how narrowly Couper had missed anticipating KekulC in announcing the idea of the linking of carbon atoms. This study led him to examine the version of Couper's salicylic acid paper that appeared in The Edinburgh New Philosophical Journal in 1858. The paper was there given in more extended form than that in which it originally appeared in the Comptes rendus of the French Academy, and Anschutz was astonished to find there the first formulas that had ever appeared in print to which the word "structural" could be applied in anything approximating to the present sense in which the term is used. The employment of connecting lines between symholssometim& dotted and sometimes continuous lines-to indicate the union of atom with atom, is there met with for the fust time, in some instances in conjunction with, but in others without, the brackets that were so profusely used in formulas based upon the chemical types. Couper's usage as regards these matters varied to some extent in different papers, and also, a t times, in the French and English versions, res~ectively,of the same idea of "stru~tnre,"in the papers, but the;nderlying present sense, is exhibited in his formulas plainly enough. Animated, on account of these different points of contact with the work of Couper, by a desire to know something of the man himself, and, as already stated, not finding any information concerning him in the usual reference books of chemical history or biography, Anschutz began, as early as 1903, to make enquiries in such directions as seemed likely to lead to the gaining of information regarding him, and it is here that "The Couper Quest" begins. The fact that Couper's papers were printed in extenso in English as well as in French journals apparently suggested enquiry in Britain, and Anschutz made early enquiry from his friend Debus, who had been professor of chemistry at the Royal Naval College, Greenwich, but who had retired to Cassel in Germany. Debus wrote to a former London acqnaintance, Greville Williams, who was for many years chemist to the London Gas Company. Williams, in response, sent to Debus the letter dated August 10, 1903, which Anschutz included in his 1906 Annulen paper on "The Action of Phosphorus Pentachloride on Substituted o-Phenol Carbonic A ~ i d s . " ~The letter runs : I mieve to sav that I know nothine of the oriein of ooor C w p u I first bcramcarqu:ainttd with him whcn I was:ts\istant to l h (:rftcrward. I.
