February 24, 19 10] 



NATURE 



50- 



Chemical Laboratory, a position which he retained — active 

 to tlie last — until 1901, when he retired in his seventy-fifth 

 year of age. 



Before his connection with the University, he founded 

 and edited, from 1S62 to 1878, in association with his 

 brother, August Thomsen, the Journal of Chemistry and 

 I'liysics, one of the principal organs of scientific literature 

 in Denmark. 



In 1863 he was elected a member of the Commission of 

 \\'eights and Measures, and was instrumental in bringing 

 about the adoption of the metric system and the assimilation 

 of the Danish system to that of the Scandinavian Kingdom. 



In 18S3 Thomsen became Chancellor of the Polytechnic 

 High School of Copenhagen — a position which he held for 

 about nine years. During this period he entirely changed 

 the character and spirit of the school, and stamped it with 

 the impress of his earnestness and industry. Under his 

 direction, new buildings were erected and arranged in 

 accordance with the best Continental and .American models. 

 Thomsen's administration was in marked contrast to that 

 of his somewhat easy-going predecessor, but it is doubtful 

 if it brought him popularity in the school. The students 

 respected and even feared him, but his cold and unsym- 

 pathetic nature evolccd no warmer feeling. It was said of 

 him by one who knew him intimately that he never learned 

 to draw the young to him, to create in them an interest 

 for his work, to form a scliool. Thomsen was a homely 

 man, but not even in his home, says the same authority, 

 was it possible for him to change his active, earnest, 

 strenuous disposition-j-what his friends called his fighting 

 character. But if he was always the serious master of the 

 house, he was also its obedient servant. In reality he was 

 a man of deep feeling, and was 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 

 chemical laboratory of the University that Thomsen 

 executed the thermochemical investigations which constitute 

 the experimental development of the ideas he had formuLited 

 in his memoir of 1S61. The results of these inquiries were 

 first made known in a series of papers published from i86g 

 to 1873 in the Transactions of the Royal Danish Society of 

 Sciences, and from 1873 onwards by the Journal fiir 

 Praktische Chcmie. The papers were republished in col- 

 lected form in four volumes (1882— 1886) bv a Leipzig house 

 under the title of " Thermocliemische Untersuchungen " A 

 summary of this experimental labour, which extended over 

 a third of a century, was subsequently prepared by Thomsen, 

 and published in 190/; in Danish under the title of " Thermo- 

 kem'ske Resultater." 



In this work he reviewed the whole of the numerical 

 and theoretical results, to the exclusion of the greater portion 

 of the experimental details. A translation of this volume 

 by Miss Katharine A. Burke, entitled "Thermochemistry,'* 

 renders it readily accessible to English readers. Miss Burke 

 has supplemented the original work by a short account, 

 taken from the " Thermochemische Untersuchungen," of 

 the experimental methods employed, therebv rendering the 

 whole more intelligible to the student. Moreover, in the 

 English edition a partial attempt has been made to translate 

 Thomsen's deductions into the language of modern theory 

 based on the conception of ionisation, which, of course, was 

 not known to science at the time the ** Thermochemische 

 Untersuchungen " was published. 



It is impossible within the limits of such a notice as 

 this to deal in detail with the immense mass of experimental 

 material which this work embodies, and I shall not attempt, 

 therefore, to do more than to offer a generalised statement, 

 based mainlv upon the admirable account jf Thomsen's 

 work given by Prof. Bronsted to the Chemical Society of 

 Copenhagen on the occasion of the meeting held on Marcii 

 2, 1909, to commemorate Thomsen's services to science. 



The conception of affinity as a cause and determining 

 condition of chemical change is traceable in some of the 

 earliest efforts to coordinate and explain chemical 

 plienomena. It certainly existed long prior to the time of 

 Bovle, and was at the basis of every philosophical system 

 after his period. We need only mention the names of 

 Bergman, Wenzel, and Berthollet to indicate this fact. 

 But to Thomsen belongs the credit of being the first to 

 make the attempt to measure the relative value or strength 



NO. 2104, VOL. 82] 



of affinity quantitatively, and to express it numerically in 

 definite terms which admitted of exact comparison. 

 Thomsen's theory of aflinity, as enunciated by him in his 

 1851 paper, was based upon his conviction that affinity 

 could be measured quantitatively by estimating the amount 

 of heat evolved in the chemical process. We are not imme- 

 diately concerned to show whether the theory is right or 

 wrong, or in what respect it fails. The point is that the 

 enunciation of this principle upwards of half a century 

 ago constituted an important step forward, inasmuch as it 

 sought to estimate affinity in relation to a quantity whicli 

 can be fi.xed by experiment, and is capable of expression 

 bv numbers. In this and in the subsequent paper of which 

 mention has been made already, he thus defines his con- 

 ception of thermochemistry, and discusses, for the first time, 

 its laws. 



'■ The force which unites the component parts of a 

 chemical compound is called affinity. If a compound is 

 split up, whether by the influence of electricity, heat, or 

 light, or by the addition of another substance, this affinity 

 must be overcome. A certain force is required the amount 

 of which depends on the strength of the aflinity. 



" If we imagine, on the one side, a compound split up 

 into its component parts, and on the other side these parts 

 again united to form the original compound, then we have 

 two opposite processes the beginning and end of which are 

 alike. It is therefore evident that the amount of the force 

 required to split up a certain compound must be the same 

 as that which is evolved if the compound in question is 

 again formed from its component parts. 



" The amount of force evolved by the formation of a 

 compound can be measured in absolute terms ; it is equal 

 to the amount of heat evolved by the formation of the 

 compound. 



" Every simple or complex action of a purely chemical 

 nature is accompanied by evolution of heat. 



" By considering the amount of heat evolved by the 

 formation of a chemical compound as a measure of the 

 affinitv, as a measrue of the work required to again resolve 

 the compound into its component parts, it must be possible 

 to deduce general laws for the chemical processes, and to 

 exchange the old theory of affinity, resting on an uncertain 

 foundation, for a new one, resting on the sure foundation 

 of numerical values." 



As has been proved by later theoretical and experimental 

 investigations, the theory of thermochemical affinity is not 

 absolutely correct at ordinary temperatures. But. on the 

 other hand, it has been shown that a comparatively large 

 number of processes are appro.ximately in unison with it. 

 Not only do they agree qualitatively, that is to say, that 

 heat is evolved during, the process, but also in the fact that 

 the results which newer and more exact methods for 

 estimating affinity have produced agree numerically with 

 what would be required by the thermochemical theory. 

 We meet here with a fundamental phenomenon which 

 Thomsen deserves great credit for having first pointed out, 

 but the explanation of which could not be given at the 

 time he intiicated it. It can be demonstrated theoretically 

 that the lower we reduce the temperature and the nearer 

 we get to the absolute zero, the more nearly is the condition 

 for the theory fulfilled, so that at the absolute zero the 

 theory would be found to be an exact law of nature. If it 

 were possible to work at such low temperatures it would be 

 found that the evolution of heat, or the evolution of 

 energy bv the chemical process, would be .'■n exact measure 

 of the affinitv of the process and that under this condition 

 the theorv of Thomsen would be the accurate expression of 

 a natural law. 



But under ordinary conditions this is not so, for in reality 

 an ever-increasing number of endothermic processes are 

 found to occur, tlnat is. processes which proceed with the 

 absorption of heat. Thomsen tried at first to explain these 

 phenomena in such a way as to keep them within his svstem, 

 and he drew a distinction between a purely chemical process 

 running conformably to his theory and a physico-chemical 

 process which did not fall within the law. But he was 

 gradually convinced that his theorv could not be maintained 

 in its entirety. It is to his credit that he did not seek to 

 uphold an untenable principle, or try to defend it as did 

 Berthelot. who almost to his dying dav maintained the 

 validity of the principle in spite of all facts. 



