THORPE : THOMSEN MEMORIAL LECTURE. 161THOMSEN MEMORIAL ;LECTURE.DELIVERED ON FEBRUARY 17TH, 1910.By SIR EDWARD THORPE, C.B., LL.D., F.R.S., Past-President of theChemical Society.AMONG the Danes whose names are inscribed as men of science onthe eternal bead-roll of fame, that of Julius Thomsen stands pre-eminent-linked indeed with that of 'Oersted. It is significant ofthe position which Thomsen acquired in physical science, and ofthe respect which that position secured for him in the eyes of hiscountrymen, that his statue should have been erected during hislifetime and placed in the vicinity of that of Oersted in the court-yard of the Polytechnic High School of Copenhagen. Thomsen, infact, played many parts in the intellectual, industrial, and socialdevelopment of Denmark.To Europe in general he was mainlyknown as a distinguished man of science. By his fellow-citizens hewas further recognised as an educationist of high ideals, actuatedby a strong common sense and a stern devotion to duty; as anable and sagacious administrator ; as a successful technologist andthe creator of an important and lucrative industry based upon hisown discoveries; and as a man of forceful character, who broughthis authority, skill, and knowledge of men and affairs to the serviceof the communal life of Copenhagen.Thomsen was a municipal councillor of that city for more thana third of a century. He occupied a commanding position on theCouncil, and was invariably listened to with respect. The gas,water, and sewage works of Copenhagen are among the monumentsto his civic activity.From 1882 up to the time of his death hewas a member of the Harbour Board of the port. I n these respectsThomsen sought to realise Priestley's ideal of the perfect man-thathe should be a good citizen first and a man of science afterwards.Hans Peter Jurgen Julius Thomsen was born in Copenhagen onFebruary 16th, 1826. He was educated a t the church school ofSt. Peter in that city, and subsequently a t von Westens Institute.I n 1843 he commenced his studies a t the Polytechnic, and in 1846graduated there in Applied Science, and became an assistant toProfessor E. A. Scharling. Of his earliest years comparativelylittle is known. Thomsen, always a reserved and taciturn man,talked little about himself even to his intimate friends-and leastof all about the days of his youth.It was known to a few thatthese days had not been smooth. Those who were 'best informedVOL. XCVII. 162 THORPE : TEOMSEN MEMORIAL LECTURE.were conscious that to these early struggles much of that dour andresolute nature which formed a distinguishing trait in his characterwas due, Thomsen, indeed, began life as a fighter, and a fighterhe remained t o the end of his four-score years.I n 1847, he became assistant to Forchhammer, passing rich, likeGoldsmith’s pedagogue, on &40 a year. Georg Forchhammer, whoseearliest work dates back to the period when Berzelius was in hisprime, was an active and industrious investigator of the old school,mainly in inorganic chemistry, and more particularly on problemsof chemical geology and physiography. He was a frequent visitorto this country, and was well known to early members of theBritish Association.Although doubtless influenced, in commonwith all teachers in Northern Europe, by the example and methodsof Berzelius, such influence as he himself was able to exert diedwith him. Forchhammer attracted few pupils, and created no school,and Thomsen probably derived no inspiration or acquired anystimulus from this association. For a time Thomsen supplementedhis scanty income by teaching agricultural chemistry at thePolytechnic. In 1853 he obtained a travelling scholarship, andspent a year in visiting German and French laboratories. Heprobably owed this scholarship in great measure to his first con-tribution to the literature of chemistry, namely, his memoir,(( Bidrag ti1 en Thermochemisk System ” (contributions to a thermo-chemical system), communicated to the Royal Society of Sciencesof Copenhagen in 1852, and for which he received the silver medalof the Society and a sum of ten guineas to enable him t o procurea more accurate apparatus. I n this memoir he sought to developthe chemical side of the mechanical theory of heat, doubtless underthe influence of Ludwig Augustus Colding, an engineer in theservice of the Municipality of Copenhagen, and a pioneer, likeMayer, in the development of that theory.Indeed, the Danes nowclaim for Colding, who had made experiments on the relationbetween work and heat as far back as 1842, but whose labours werepractically ignored by his contemporaries, the position which theGermans assign to Mayer (see Mach’s ‘( Development of the Theoryof Heat”).I n 1861 Thomsen further developed his ideas in amemoir on the “ General Nature of Chemical Processes, and on aTheory of Affinity Based Thereon,” published in the Transactions ofthe Danish Academy of Sciences. I n this paper he laid theroundations of the chief scientific work of his life.I n 1853 Thomsen patented a method of obtaining soda fromcryolite, so-called ‘‘ Greenland,” or ice-spar, a naturally occurringfluoride of sodium and aluminium, A12F,,GNaF, found largely,indeed, almost exclusively, in Greenland, and particularly a THORPE : THOMSEN MEMORIAL LECTURE.163Ivigtut. It derives its mineralogical name from its ice-likeappearance and ready fusibility even in the flame of a candle. Itseems to have been first brought to Europe in 1794, and to havebeen described by Schumacher in the following year. Klaprothfirst showed that it contained soda, and its composition was furtherestablished by Vauquelin, Berzelius, and Deville.Thomsen’s process consists in heating a finely divided mixture ofcryolite and chalk in a reverberatory furnace, whereby carbondioxide is expelled and calcjum fluoride and sodium aluminateare formed. The roasted mass is lixiviated with water, so asto dissolve out the sodium aluminate, which is then treated withcarbon dioxide. Alumina is precipitated, and sodium carbonateremains in solution. The aIumina is either sold as such, or con-verted into sulphate (so-called ‘‘ concentrated alum ” or “ alum-cake ”), and the sodium carbonate is separated by crystallisation.Both products are obtained in a remarkably pure condition, and thecryolite-soda, yields excellent “ caustic.”Thomsen’s process, although simple enough in principle, requiresconsiderable skill and pains in its practical execution, and most ofthe manufacturing details were worked out by him, or under hisdirection.Success largely depends upon the maintenance of aproper temperature ; the decomposition begins below a red-heat, butrequires to be finished at that temperature, and care must be takento avoid fusion or even sintering of the mass.In 1854 Thomsenobtained tho exclusive right of mining for cryolite and of workingup the mineral in Denmark for soda and alumina. Actual manu-facturing operations were begun on a small scale in 1857, and in thefollowing year Thomsen planned the present large facbry a tOeresund, near Copenhagen, which was opened on his thirty-fourthbirthday. The importance of this industry to Denmark may beseen from the circumstance that during the fifty years of itsexistence the firm have paid the Danish Government nearlyS300,OOO for the concession. Other factories were started inGermany, Bohemia, and Poland, but met with little success. ThePennsylvania Salt-manufacturing Company at Natrona, nearPittsburg, eventually obtained the right to work up two-thirds ofall the cryolite mined in Greenland.From the start Thomsen tooka large share in the management of the Oeresund works, and byhis energy, foresight, and skill placed the undertaking on a soundcommercial basis.Although Thomsen died a rich man, mainly as the result of theindustry he created, in the outset of his career as a, teacher and atechnologist his means were very straitened. He came of poorparents, of no social position or influence, and they were unable toM 164 THORPE : THOMSEN MEMORIAL LECTURE.further his inclinations towards an academical career. I n 1854 heapplied unsuccessfully for a position as teacher of chemistry a t theMilitary High School in Copenhagen. During three years-from1856 to 1859-while still engaged in developing his cryolite process,he acted as an adjuster of weights and measures to the Municipalityof Copenhagen.It was a poorly paid position, but it kept thewolf from the door. A t about this period he betook himself toliterature, and published a popular book on general subjects con-nected with physics and chemistry-somewhat in the style ofHelmholtz’s well-known work-entitled ‘‘ Travels in ScientificRegions,” which had a considerable measure of success. He was,however, not altogether unknown even at this time as an author,since in 1853 he had collaborated with his friend Colding inproducing a memoir on the causes of the spread of cholera and onthe methods of prevention, which attracted much attention at thetime of its appearance.I n 1859, whilst engaged in the Oeresund factory, he againapplied to the authorities for a position as teacher a t the MilitaryHigh School, and succeeded in obtaining an appointment to alectureship in physics, which he held until 1866.During his tenureof this office he devised his polarisation battery, which receivedmany awards at International Exhibitions and was used for a timein the Danish telegraph service.I n 1859-60 he was “vicarius” for Scharling at the University,and in 1865 became a teacher, and in the following year Professorof Chemistry and Director of the Chemical Laboratory, a positionwhich he retained-active to the last-until 1901, when he retiredin his seventy-fifth year of age.Before his connexion with the University, he founded a d edited,from 1862 to 1878, in association with his brother, August Thomsen,the Journal of Chemistry and Physics, one of the principal organsof scientific literature in Denmark.I n 1863 he was elected a member of the Commission of Weightsand Measures, and was instrumental in bringing about the adoptionof the metric system and the assimilation of the Danish system t othat of the Scandinavian Kingdom.I n 1883 Thomsen became Chancellor of the Polytechnic HighSchool of Copenhagen-a position which he held for ,about nineyears. During this period he entirely changed the character andspirit of the school, and stamped it with the impress of his earnest-ness and industry. Under his direction, new buildings were erectedand arranged in accordance with the best Continental and Americanmodels.Thomsen’s administration was in marked contrast to thatof his somewhat easy-going predecessor, but it is doubtful if i THORPE : THOMSEN MEMORIAL LECTURE. 165brought him popularity in the school. The students respected andeven feared him, but his cold and unsympathetic nature evokedno warmer feeling. It was said of him by one who knew himintimately that he never learned to draw the young to him, tocreate in them an interest for his work, to form a school. Thomsenwas a homely man, but not even in his home, says the sameauthority, was it possible for him to change his active, earnest,strenuous disposition-what his friends called his fighting character.But if he was always the serious master of the house, he was alsoits obedient servant.I n reality he was a man of deep feeling, andwas not without power to give that feeling expression in words,sometimes in verse, and occasionally even in music.It was while occupying the position of Director of the ChemicalLaboratory of the University that Thomsen executed the thermo-chemical investigations which constitute the experimental develop-ment of the ideas he had formulated in his memoir of 1861. Theresults of these inquiries were first made known in a series ofpapers published from 1869 to 1873 in the Transactions of the RoyalDanish Society of Sciences, and from 1873 onwards b,y the Journalfiir Praktische Chemie. The papers were republished in collectedform in four volumes (1882-1886) by a Leipzig house under thetitle of Thermochemische Untersuchungen.A summary of thisexperimental labour, which extended over a third of a century,was subsequently prepared by Thomsen, and published in 1905 inDanish under the title of Thermokemiske Resultater.I n this work he reviewed the whole of the numerical andtheoretical results, to the exclusion of the greater portion of theexperimental details. A translation of this volume by MissKatharine A. Burke, entitled Thermochernistry,” renders itreadily accessible to English readers. Miss Burke has supple-mented the original work by a short account, taken from theThermoc7bem’sche Unt ersuchungen, of the experimental methodsemployed, thereby rendering the whole more intelligible to thestudent.Moreover, in the English edition a partial attempt hasbeen made to translate Thomsen’s deductions into the language ofmodern theory based on the conception of ionisation, which, ofcourse, was not known to science at the time the ThermochemisclieUntersuchungen was published.It is impossible within the limits of such a notice as this to dealin detail with the immense mass of experimental material whichthis work embodies, and I shall not attempt, therefore, to do morethan to offer a generalised statement, based mainly upon theadmirable account of Thomsen’s work given by Professor Bronstedto the Chemical Society of Copenhagen on the occasion of th166 THOltPE : THOMSEN MEMORIAL TJECTURE.meeting held on March 2nd, 1909, t o commemorate Thomsen’sservices to science.The conception of affinity as a cause and determining conditionof chemical change is traceable in some of the earliest cfforts toco-ordinate and explain chemical phenomena.It certainly existedlong prior to the time of Boyle, and was a t the basis of everyphilosophical system after his period. TT7e need only mention thenames of Bergman, Wenzel, and Berthollet to indicate this fact.But to Thomsen belongs the credit of being the first t o make theattempt to measure the relative value or strength of affinityquantitatively, and to express it numerically in definite termswhich admitted of exact comparison. Thomsen’s theory of affinity,as enunciated by him in his 1851 paper, was based upon his con-viction that affinity could be measured quantitatively by estimatingthe amount of heat evolved in the chemical process.We are notimmediately concerned to show whether the theory is right orwrong, or in what respect it fails. The point is that the enunciationof this principle upwards of half a century ago constituted animportant step forward, inasmuch as it sought t o estimate affinityin relation to a quantity which can be fixed by experiment, and iscapable of expression by numbers.I n this and in the subsequent paper of which mention has beenmade already, he thus defines his conception of thermochemistry,and discusses, for the first time, its laws.“The force which unites the component parts of a chemicalcompound is called affinity. I f a compound is split up, whetherby the influence of electricity, heat, or light, or by the additionof another substance, this affinity must be overcome. A certainforce is required the amount of which depends on the strength ofthe affinity.“ I f we imagine, on the one side, a compound split up into itscomponent parts, and on the other side these parts again unitedto form the original compound, then we have two opposite processesthe beginning and end of which are alike.It is therefore evidentthat the amount of the force required to split up a certain compoundmust be the same as that which is evolved if the compound inquestion is again formed from its component parts.‘I The amount of force evolved by the formation of a compoundcan be measured in absolute terms; it is equal t o the amount ofheat evolved by the formation of the compound.(( Every simple or complex action of a purely chemical nature isaccompanied by evolution of heat.‘(By considering the amount of heat evolved by the formationof a chemical compound as a measure of the affinity, as a measurTHORPE : THOMSEN MEMORIAL LECTURE.167of the work required again to resolve the compound into itscomponent parts, it must be possible to deduce general laws for thechemical processes, and to exchange the old theory of affinity,resting on an uncertain foundation, for a new one, resting on thesure foundation of numerical values.”As has been proved by later theoretical and experimental investi-gations, the theory of thermochemical affinity is not absolutelycorrect a t ordinary temperatures.But, on the other hand, it hasbeen shown that a comparatively large number of processes areapproximately in unison with it. Not only do they agree quali-tatively, that is to say, that heat is evolved during the process, butalso in the fact that the results which newer and more exactmethods for estimating affinity have produced, agree numericallywith what would be required by the thermochemical theory. Wemeet here with a fundamental phenomenon which Thomsen deservesgreat credit for having first pointed out, but the explanation ofwhich could not be given at the time he indicated it. It can bedemonstrated theoretically that the lower we reduce the tempera-ture and the nearer we get to the absolute zero, the more nearly isthe condition for the theory fulfilled, so that at the absolute zerothe theory would be found to be an exact law of nature. I f it werepossible to work a t such low temperatures it would be found thatthe evolution of heat, or the evolution of energy by the chemicalprocess, would be an exact measure of the affinity of the process,and that under this condition the theory of Thomsen would be theaccurate expression of it natural law.But under ordinary conditions this is not so, for in reality anever-increasing number of endothermic processes are found tooccur, that is, processes which proceed with the absorption of heat.Thomsen tried a t first to explain these phenomena in such a wayas to keep them within his system, and he drew a distinctionbetween a purely chemical process running conformably to histheory and a physico-chemical process which did not fall withinthe law.But he was- gradually convinced that his theory couldnot be maintained in its entirety. It is to his credit that he didnot seek to uphold an untenable principle, or try to defend it asdid Berthelot, who almost to &is dying day maintained the validityof the principle in spite of all facts.These ideas have, in the words of Ostwald, been the scientificconfession of faith of chemists throughout half a century. Theyhave had the greatest influence on scientific thought in everybranch of chemistry. It is on the basis of them that we havearrived a t a theory of affinity which at the present moment isbeing developed into one of the most perfect chemical theories168 THORPE : THOMSEN MEMORIAL LECTURE.Lastly, it is due to these ideas that the experimental material hasbeen produced which during all time will place the name of JuliusThomsen in the first rank of men of science.To go through this material in detail is, as I have said, impossiblehere.It may be stated generally that practically every simpleinorganic process has been investigated calorimetrically byThomsen, or can be calculated by means of the calorimetric datafurnished by him. I n the case of organic substances, data have beengiven for estimating the heat of combustion of a large number ofcompounds. All these estimations were made by Thomsen per-sonally, according to a pre-arranged plan, and in systematic suc-cession during a period of more than thirty years. They comprisemore than 3500 calorimetrical estimations.It has been truly saidthat this work is unique in the chemical history of any country.Among the results of Thomsen’s thermochemical inquiries whichhave special value for physical chemistry is his investigation of thephenomena of neutralisation, in which he shows that the basicityof acids can be estimated thermochemically, and that it can in thisway be proved whether or not a point of neutrality exists. Hisobservation that the heat of neutralisation is the same for along series of inorganic acids, such as hydrochloric acid, hydro-bromic acid, hydriodic acid, chloric acid, nitric acid, etc., supportsthe theory of electrical dissociation, inasmuch as this requires thatthe heat of neutralisation of the strong acids must in all cases beindependent of the nature of the acid, because the process ofneutralisation for all of them is the combination of the ion of’hydrogen in the acid with the ion of hydroxyl of the base to formwater.These investigations also led to the important thermo-chemical result that the heat of neutralisation of acids (or the heatof their dissociation) cannot be considered as a measure of thestrength of the acids.Another important result is the proof by experiment of theconnexion which exists between the changes of the heat-effect withthe temperature and the specific heat of the reacting substances.The first law of thermodynamics requires the relation indicatedwhere U is the heabeffect, T the by Kirchhoff : d-T =C, -Cz, dUtemperature? and C, and C2 are the heat capacities of t,he twosystems before and after the reaction, and Thomsen showed byinvestigation of the heat of neutralisation, the heat of solution, andthe heat of dilution, that this relation was satisfied For thepurpose of his inquiry, the specific heats of a large number ofsolutions of salts were estimated by an ingenious method, andwith an exactness hitherto unattainedTHORPE : THOMSEN MEMORIAL LECTURE.169Of no less importance are Thomsen’s thermochemical investi-gations on the influence of mass. I n the year 1867 Guldberg andWaage published their theory of the chemical effect of mass.Butthey had only verified the theory to a small extent and in par-ticularly simple cases. They had not investigated the completehomogeneous equilibrium, because at that time no method existedfor experimental investigation of such homogeneous equilibrium.Thomsen showed that the estimation could be made thermo-chemically. By allowing, f o r instance, an acid to act on a saltof another acid in an aqueous solution, the latter acid will bepartly replaced by the first, which will form a salt. By mixing,for instance, a solution of sodium sulphate and nitric acid, thereis formed sodium nitrate and sulphuric acid, but the process willnot proceed to completion. I f we have estimated the heat ofneutralisation of the two acids with sodium hydroxide, the differencebetween these two heat-phenomena will give the amount of heatcorresponding to the total decomposition of the sodium sulphate,and the heat found experimentally by mixing the two solutions willtherefore show to what degree the transformation has taken place.It would be possible to estimate thermochemically the amount ofthe four substances in solution, and thereby, by varying the con-centration or the proportion between the initial quantities ofsubstances, to calculate whether the Guldberg-Waage theory on theeffect of mass was confirmed in this case.Thomsen applied this method to a large number of differentacids and bases, and was enabled thereby to prove the agreementwith the law of the influence of mass in all the cases which heexamined.He found particularly that the proportion of theone acid which remained combined with the base wits constantwith mixtures of constant proportion. On this basis he propoundedthe term avidity, which he defined as the tendency of the acid tounite with the base, and he showed that the avidity was independentof the concentration, and only to a small extent varied with thetemperature. The term avidity has since acquired great importance,particularly since other and more exact methods for its estimationhave been found. Concurrently with this, its meaning has beenmade clear by the theory of electrolytic dissociation.On the basis of these estimations, Thomsen drew up the firsttable, based on experiments, of the relative strength of the acids,and the numbers in this table have been found to agree with theresults obtained by examining the electrical conduct.ivity of theacids.It is worth noting that Thomsen not only produced the experi-mental proof of the correctness of the Guldberg-Waage theory o170 THORPE : THOMSEN MEMORIAL LECTURE.the effect of mass soon after the appearance of this theory, butalso that he was the first to acknowledge and adopt it.It isremarkable that this work of Thomsen received so little attention,although it appeared in a widely circulated German journal, andit was not until ten years later that the law of the effect of masswas generally recognised, as the result of the work of Ostwald andvan’t Hoff.Although Thomsen’s title to scientific fame rests mahly uponhis thermochemical work, his interests extended beyond this par-ticular department of physical chemistry.IIe worked on chloralhydrate, selenic acid, on ammoniacal platinum compounds, and onglucinum platinum chloride, on iodic acid and periodic acid, onhydrogen peroxide, hypophosphorous acid, and hydrogenium. Heearly recognised the importance of MendelBeff’s great generalisation,and contributed to the abundant literature it produced. His paperof 1895, ((On tho Probability of the Existence of a Group ofInactive Elements,” may be said to have foreshadowed thediscovery of the congeners of argon. He pointed out that inperiodic functions the change from negative to positive value, orthe reverse, can only take place by il passage through zero orthrough infinity; in the first case, the change is gradual, and inthe second case it is sudden.The first case corresponds with thegradual change in electrical character with rising atomic weight inthe separate series 01 the periodic system, and the second casecorresponds with a passage from one series to the next. It thereforeappears that the passage from one series to the next in the periodicsystem should take glace through an element which is electricallyindifferent. The valency of such an element would be zero, andtherefore in this respect also it would represent a transitional stagein the passage from the univalent electronegative elements of theseventh to the univalent electropositive elements of the first group.This indicates the possible existence of a group of inactive elementswith the atomic weights 4, 20, 36, 84, 132, the first five numberscorresponding fairly closely with the atomic weights respectivelyof helium, neon, argon, krypton, and xenon (Zeitsch.anorg. Chem.,1895, 9, 283; Jourm. Chem. Soc., 1896, 70, 11, 16). He subse-quently made known the existence of helium in the red fluoritefrom Ivigtut.As evidence of Thomsen’s manipulative ability and his powerof accurate work may be mentioned his determination of the atomicweights of oxygen and hydrogen, and incidentally of aluminium.For the atomic weight of hydrogen he obtained the value 1.00825when 0 = 16, which is practically identical with that of Morley andNoyes. He further made most accurate estimations of the relativTRORPE : THOMSEN MEMORIAL LECTURE.171densities of these gases, and of the volumetric ratios in which theyenter into the composition of water. His value for the atomicweight of aluminium is nearly identical with that adopted in thelast Report of the 1nterna.tion;tl Committee on Atomic Weights.Thomsen maintained his interest in thermochemical problems upto the end, and was a keen and clear-sighted critic of the workwhich appeared from time t:, time during the later years of hislife. This interest occasionally gave rise to controversy, and someof his latest papers were wholly polemical.Thomsen was a pronounced atomist, and t o him a chemicalprocess was a change in the internal structure of a molecule, andthe chief aim of chemistry was to investigate the laws whichcontrol the union of atoms and molecules during the chemicalprocess.He considered that chemistry should be treatedmathematically as a branch of rational mechanics. But no oneinsisted more strongly than he how little we really know of thescquestions. I n summarising his tlicoreticnl ideas in the TAewn o-Eemische Resiiltcitcr, he says, “ An almost impenetrable darknesshidzs from us the inner structure of molecules and the true natureof atoms. We know only the relative number of atoms withinthe molecule, their mass, and the existence of certain groups ofatoms or radicles in the molecule, but with regard to the forcesacting within the molecules and causing their formation or destruc-tion our knowledge is still exceedingly limited.” He fully realisedthat his own work was only the foundation on which the futureelucidation of these questions must rest.“ H e worked,” saysBronsted, “ in the conviction that what we somewhat vaguely callthe affinity of the atoms-their interaction, their attraction, andvarying effect, etc.-follows the general laws of mechanics, and that,as lie worded it, the principle that ‘might is right,’ holds good inchemistry as in mechanics. ‘On this foundation he hoped to beable to evolve the laws for the statics and dynamics of chemicalphenomena, even although the true nature of the action isunknown.”Thomsen’s merits as an investigator received formal recognitionfrom nearly every country in the civilised world.As far back as1860 he was elected one of the thirty-five members of the DanishRoyal Society of Sciences of Copenhagen, and from 1858 until hisdeath he was its President. I n 1876 he became an HonoraryForeign Member of the Chemical Society of London. On theoccasion of the fourth centenary of the foundation of the Universityof Upsala (created in 14$7), he received the degree of Doctor ofPhilosophy honoris causa. I n 1879 he was made an honorary M.D.of the University of Copenhagen. Two years later he was made i172 THORPE : THOMSEN MEMORIAL LECT’C’RE.Foreign Member of the Physiographical Society of Lund, and in1888 he was elected a member of the Society of Science andLiterature of Gothenburg. I n 1885 he became a member of theRoyal Society of Sciences of Upsala, and in 1886 of the StockholmAcademy of Sciences.I n 1883 he and Berthelot were together awarded the DavyMedal of the Royal Society-a fitting and impartial recognition onthe part of the Society of the manner in which the two investigators,whose work not infrequently brought them into active opposition,had jointly and severally contributed to lay the foundations ofthermochemistry .I n the same year Thomsen wits made a member of the Accademiadei Lincei of Rome, and in the following year he was elected intothe American Academy of Arts and Sciences in Boston, and of theRoyal Academy of Sciences of Turin. I n 1887 he was made amember of the Royal Belgian Academy.I n 1886-87 and again in 1891-92 he was Rector of the Universityof Copenhagen. I n 1888 he became Commander of the Dannebrog,and in 1896, and on his seventieth birthday, he was made GrandCommander of the same order. On the same occasion the Danishchemists caused a gold medal t o be struck in his honour. I n 1902he became a Privy Councillor (Geheime Konferenz raad). I n thesame year he was elected a Foreign Member of the Royal Societyof London.He died on February 13th, 1908, full of years as of honours,and was buried on the eighty-third anniversary of his birth andon the jubilee of the opening of the Oeresund factory. His wife,Elmine Hansen-the daughter of a farmer on LangeIand-pre-deceased him in 1890.I desire to express my acknowledgments to Director G. A.Hagemann, of Copenhagen, and t o Professor Arrhenius, ofStockholm, for their assistance in obtaining information concerningThomsen’s personal history. I a,m also much indebted to ourFellow, Mr. Haralcl Faber, for his kindness in making for mea transhtion of Professor Bronsted’s accoiint of Thomsen’s scientificwork, on which my own r6sum6 is mainly based