47S 



NATURE 



[September 12, 1895 



1SS7, Planck having almost simultaneously arrived at similar 

 \news on other grounds. 



Closely connected with electrolysis is the question of the con- 

 stitution of solutions, and here again a convergence of work 

 from several distinct fields has led to the creation of a new 

 branch nf physical chemistry which may be considered a modern 

 growth. The relationship twtween the strength of a solution 

 and its freezing point had been discovered by Blagden towards 

 the end of the last centur)-, but in 1851 chemists had no notion 

 that this observation would have any influence on ihe future de- 

 velopment of their science, .\nother decade elapsed before the 

 law was re<liscovere<l by Rudorff(lS6l), and ten years later vsas 

 further elaborated by de Coppet. Raoult published his first work 

 on the freezing point of solutions in 1882, and two years later the 

 relationship l>etween osmotic pressure and the lowering of freez- 

 ing point was established by H. de \'ries, who first a|>proached 

 the subject as a physiologist, through obser\ations on Ihe cell 

 contents of living plants. .As the work done in connection with 

 osmotic pressure has had such an important influence on the 

 "dissociation" theor)' of solutions, it will be of interest to note 

 that at the last Ipswich meeting Thomas Clraham made a com- 

 munication on liquid diffusion, in which he " gave a view of 

 some of the unpublished results, to ascertain whether solutions 

 of saline bodies had a power of diffusion among liquids, espe- 

 cially water." In 1877 Pfefler, who, like de \'ries, entered the 

 field from the botanical-physiological side, succeeded in efl'ecting 

 the measurement of osmotic pressure. Ten years later van "t 

 Hoff formulated the nnxlern dissociation theory of solution by 

 apphing to dissolved substances the laws of Boyle, Gay-Lussac, 

 and .-Vvi^adro, the law of osmotic pressure, and Raoult's law- 

 connecting the depression of freezing ]X)int with molecular 

 weight, thus laying the foundation of a doctrine which, whether 

 destined to survive in its present form or not, has certainly 

 exerted a great influence on contemporary chemical thought. 



Consider, further, the state of knowledge in 1851 concerning 

 such leading principles as dissociation or thermolysis, ma.ss 

 action, and chemical equilibrium. Abnormal vapour densities 

 had been observed by .\vogadro in 181 1, and by Ampere in 

 1814. Grove had dissociated water vapour by heat in 1847, but 

 the first great advance was made ten years later by Sainte-Claire 

 Dcvillc, from whose work has emanated our existing knowledge 

 of this subject. I may add that the application of this principle 

 to explain the cases of abnormal vapour density was made in 185S 

 by Kopp, Kekule, and Cannizzam almost simultaneously ; but, 

 strangely enough, this explanation was not acccjiled by Deville 

 himself. The .subsequent stages are subjects of modern history. 

 The current views on mass action were foreshadowed, as is well 

 known, by BerthoUet in his " Statique Chimique," published in 

 1803, but no great advance had been made when ihe British 

 A.ss<iciation last met here. The subject first began to .-issume a 

 quantitative aspect through the researches of Kunscn and Debus 

 in 1853, and was much advanced by (Iladstone in 1865 and by 

 Harcourt and Esson a year later. Guldberg and VVaage pub- 

 lished their classical work on this subject in 1867. 



E<|ually striking will appear the advances made since 1851 if 

 we consider that the whole subject of spectrum analysis, which 

 brings our science into relationship with astronomy, has been 

 called inio exi<>tcncc since that date. The celebrated work of 

 Bunsen and Kirchhoff w.is not published till 1859. Neither can 

 I refrain from reminding you that the coal-tar colour industry, 

 with which I havelwen to a small extent connected, was started 

 into activity by Pcrkin's discovery of mauve in 1856 ; the 

 reaction of this mduslry on the development of organic chemistry 

 n now too well known to re<|uire further mention. In that 

 dire-- ■ ■' which brings chemistry into relatiimship with 

 biol :rcss has lieen sf) great that it is not going beyond 



the I that anew science h.is Ixjcn crcateil. Pasteur 



liegan his studies on fermentation in 1857, and out of that work 

 ha.'s .Tri--en the icienre of lacteriology, with its multifarious and 

 nces. As this chapter of chemical history 

 'lie of Ihe evening disc<iurses at the present 

 r- to dwell further upm il now. One 

 rhronicle<l among the great develop- 

 I I refer to the periiKlic law connect- 

 1 the chemical elements with their 

 <rtieH. Allempts to establish numer- 

 ical I ■• III iwilaled groups of elements had 

 licci 11 1817, by r.Mielin in 1826, and again 

 by 1 ior..r'in. r m j ^jo. The triad system of grouping wa.s 

 Airthcr developed Ij)- Dumas in 1851. lam informed by Dr. 



farr 



Torn 



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met 



ing 



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Gladstone that at the last Ipswich meeting Dumas" speculations 

 in this direction excited much interest. All the later steps of 

 importance have, however, been made since that time, viz. by 

 de Chancourtois in 1S62. the " law of octaves" by Newlands in 

 1864, the periodic law by MendeleelT, and almost contempora- 

 neously by Lothar Meyer in 1S69. 



I have been tempted into giving this necessarily fragmentary 

 and possibly tedious historical sketch because it is ajiproaching 

 half a centurj- since the British Association visited this town, 

 and the opportunity seemed favourable for going through that 

 process which in commercial affairs is called " taking stock." 

 The result speaks for itself. Our students of the present time 

 who are nourished intellectually by these doctrines shotild be 

 made to realise how rapid has been their development. The 

 pioneers of our science, on whose shoulders we stand — and many 

 of whom are ha])pily still among us — will derive satisfaction from 

 the retrospect, and will admit that their labours have borne 

 goodly fruit. It is not, however, simply for the purpose o. 

 recording this enormous progress that I have ventured to assume 

 the oflice of stock-taker. The year 1S51 may be regarded as 

 occurring towards the close of one epoch and the dawn of a new 

 era in chemical history. Consider broadly the stale of organic 

 chemistry at that time. There is no occasion for going into 

 detail, even if time admitted, because our literature has recently 

 been enriched by the concise and excellent historical works of 

 Schorlentmer and of Ernst von Meyer. It will suffice to men- 

 tion that the work and writings of Liebig, Berzelius, Woliler, 

 Dumas, Gay-Lussac, Bunsen, and others had given us the lead- 

 ing ideas of isomerism, substitution, comiwund r.ulicles, and types. 

 Wurlz and I lofmann had just discovered the organic ammonias ; 

 Williamson that .same year made known his celebrated work on 

 the ethers ; and Gerhardt discovered the acid anhydrides a year 

 later. The newer theory of type was unilergoing development 

 by Gerhardt and his followers ; the mature results were pub- 

 lished in the fourth volume of the "Traite de Chimic" in 1S56. 

 In this country the theory was much advanced by the writings of 

 Odiing and Williamson. 



Subsequent Development ok Ciiicmistky along 

 Two Lines. 

 The new era which was dawning upon us in 1 85 1 was that of 

 structural or constitutional chemistry, based on the doctrine of 

 the valency of the atoms. It is well known that this conception 

 w.as broached by I'rankland in 1852, as the result of his investi- 

 gations on the organo-metallic compounds. But it was not till 

 1858 that Kekule, who had previously done much to develop 

 the theory of types, and CouiK-r, almost simultaneously, recog- 

 nised the quadrivalent character of carbon. To altempl to give 

 anything appro.aching an .adequate notion of the subsequent 

 inlluence of this idea on the progress of organic chemistry would 

 be tantamount to reviewing the present condition of that subject. 

 I imagine that no conception more prolific of results has ever 

 been introduced into any ileparlmvnt of science. If we glance 

 liack along the stream it will be seen that shortly after the last' 

 meeting here the course of di.scovery began to concentrate itself 

 into two channels. In one we now find the results of the con- 

 fluent labours of those who have regariled our science from its 

 physical side. In the other channel is flowing the tide of dis- 

 covery arising from the valency doctrine and its extension to th* 

 structure of chemical molecules. The two channels are at 

 present fairly |x>rallel and not far ajiart ; an occasional explorer 

 endeavours now and again to make a cross-cut so as to put the 

 streams into cimimunication. The currents in both are ruiuiing 

 very rapi<lly, and the wiirker who has embarked on one or the 

 other finds himself hurried along at such a p.ice that iIrtc is 

 hardly breathing time to step ashore and see what his neighbour* 

 arc doing. It speaks well for the fertility of the conception of 

 valency that the current in this channel is flowing with unabated 

 vigour, although its catchment area— to pursue the metaphor — is 

 by no me.ans so extensive as that of the neighbouring stream. 



The nuxlern tendency to specialisation, which is a necessity 

 arising from the large number of workers and the rapid multipli- 

 cation of results, is apparently in the two directions indicated. 

 We have one class of workers ilealing w ith the physics of matter 

 in relation to general chemical properties, and another class of 

 investigators concerning themselves with the special properties of 

 individual compounds and cla-sses of compounds with atomic 

 idiosyncrasies. The workers of one class are dirierenliating 

 while their colleagues are integrating. It would be nothing less 

 than unscientific to institute a com|xirison between the relative 1 



NO. 1350, VOL. 52] 



