September 12, 19 12] 



NATURE 



45 



to Gay-Lussac in Paris, proved that silver fulminate 

 and silver cyanate, though distinct substances, had 

 exactly the same composition ; thus was opened that 

 great chapter in the hfstory of chemistry which 

 Berzelius named isomerism. Perhaps nothing in 

 chemistry has given rise in recent years to more intel- 

 lectual and practical activity than isomerism. 

 Wohler's classical synthesis of urea, by the metastasis 

 of amnioniuni cyanate, added another instance of 

 isomerism, and Berzelius soon afterwards announced 

 the isomerism of tartaric and racemic acids. Wohler's 

 synthesis of urea, followed, as it was, by numerous 

 other laboratory syntheses, showed that substances 

 which occur in living organisms are not different 

 from those which may be prepared artificially, and 

 the old distinction between inorganic and organic 

 chemistry disappeared — there is, of course, only one 

 chemistry. The words, it is true, have survived, but 

 only for reasons of practical convenience. 



After isomerism the next great step forward in the 

 study of intra-molecular structure was the discovery 

 of groups partially individualised which are capable 

 of remaining intact through many reactions. Gay- 

 Lussac had previously noticed the cyanogen group as 

 common to cyanides ; but it was the celebrated paper 

 by Wohler and Liebig on the radical of benzoic 

 acid which finally established the existence of com- 

 pound radicals or groups such as benzoyl, and ob- 

 tained for the theory of compound radicals the posi- 

 tion in chemistry it now Isolds. Bunsen followed 

 somewhat later with the discovery of cacodyl, and now 

 such groups are almost innumerable. In many 

 respects, by the e.xperimental skill which it shows, 

 the clearness of its logical method, and the beauty of 

 its form and diction, this memoir is a model of what 

 a scientific communication should be. I will read the 

 opening paragraph, using Hofmann's translation : — 

 " When a chemist is fortunate enough to encounter, 

 in the darksome field of organic nature, a bright point 

 affording him guidance to the true path by following 

 which he may hope to explore the unknown region, he 

 has good reason to congratulate himself, even though 

 he may be conscious of being still far from the desired 

 goal." Of this memoir Berzelius, in a letter quoted 

 by Hofmann (Faraday lecture), says : — "The facts put 

 forward by you give rise to such considerations that 

 they may well be regarded as the dawn of a new day 

 in vegetal (organic) chemistry." 



The history of the advance of chemistry since the 

 days of the Giessen laboratory is bewildering in its 

 extent. This has been largely due to the Giessen 

 laboratory itself, which sent trained investigators, 

 each carrying with him some touch of its master's 

 magic, into all civilised lands. I cannot attempt to 

 even catalogue the results here. One thing may be 

 said, that chemistry is not worked out, as some have 

 thought ; but rather the opportunities of discover)' 

 seem greater and more promising than at any previous 

 period. 



Part II. 



Sub-atoms, Atoms, Molecules, Molecular Aggregates ; 



Valency. 



Whether in the light of recent researches it may 

 become necessary to give up that portion of Dalton's 

 theory of atoms in which he regards them as un- 

 decomposable and indivisible ; or whether we may 

 consider them, as Prout suggested a hundred years 

 ago, as different aggregates of sub-atoms of a uniform 

 kind of matter ; or whether they must be regarded 

 as complexes built in the manner sup_posed by the 

 electron hypothesis ; also what should be our attitude 

 towards the related problem of transmutation — all this 

 I pass over, the more willingly that these subjects 

 were discussed so recently by so high an authority 

 NO. 2237, VOL. 90] 



as Sir William Ramsay in his address to the Associa- 

 tion last year at Portsmouth. 



I assume that we are fairly satisfied with our 

 present atoms and their respective weights, and this 

 no matter how the atoms are constructed, and that 

 we shall be satisfied with them so long as they disport 

 themselves in chemical changes as indivisible entities. 

 And further, I assume that we are satisfied with our 

 molecules and their respective weights, as determined 

 by the application of Avogadro's hypothesis. Whether 

 the molecular weight is obtained by direct determina- 

 tion of gaseous density or by taking advantage of 

 the properties of dilute solutions, in either case the 

 molecular weight which results is the weight of a 

 supposed gaseous molecule, for the latter method 

 depends for its justification on the former. All our 

 molecular weights are weights of molecules in the 

 gaseous state or are supposed to be ; they are not 

 necessarily applicable to liquids, and much less to 

 solids : solids and liquids may well consist of far 

 more complex particles. 



Gradually the central problem of chemistry has 

 become more and more the study of internal structure 

 of molecules — of gaseous molecules. The enormous 

 number and variety of the compounds of carbon, with 

 which so many workers have enriched the science 

 during the last hundred years, and the special adapt- 

 ability of these compounds to the experimental study 

 of molecular structure, have led investigators to make 

 use of them rather than of the so-called inorganic 

 compounds : thus out of inquiries into the intra- 

 molecular structure of these compounds arose and were 

 developed the theories of types of Gerhardt, William- 

 son, and Kekuld. These are now, however, looked 

 upon more as aspects of the general problem. More 

 fruitful has been the study of the compound radicals 

 or individualised groups of Wohler and Liebig. But 

 gradually these molecular structures have been 

 regarded, in agreement with the views of Dumas, as 

 complete wholes ; like fairy teinples, which from 

 different points of view show different y^arts in relief, 

 accentuating, it may be, this or that column or frieze 

 or pediment. Kekule's brilliant and suggestive theory 

 of chain compounds and ring compounds did more 

 than anv other theory to guide and stimulate research 

 in chemistry in recent times. Like Gay-Lussac's 

 theory of gaseous combination, though built in the 

 first place only upon a few facts, this theory has 

 proved true of the thousands of others with which 

 we have since become acquainted ; there seems indeed 

 to be a need of a new psychology to account for such 

 truly marvellous foresight as is here exhibited. The 

 atoms forming these varied structures were, however, 

 regarded as being arranged in a plane, until the great 

 discoveries of Pasteur made it necessary for chemists 

 to extend their conceptions and to frame hypotheses 

 of three dimensions. Thus have arisen in the hands of 

 Le Bel and van't Hoff and others our modern theories 

 of stereo-chemistry. When isomerism occurs in an 

 element Berzelius names it allotropy. It seems to me 

 that now, when molecules of the elements do not 

 differ essentially from molecules of compounds, there 

 is no longer any distinctive meaning in the term, and 

 that it rnight well be abandoned. I would like also 

 to make another suggestion respecting nomenclature : 

 that when we distinguish ring compounds as cyclic 

 we might appropriately adopt the word hormathic 

 (from the Greek word for a chain or a row) for chain 

 compounds. 



But in order to understand the linking of atoms in 

 these molecular edifices some combining value had to 

 be assigned to the different atoms. This idea of 

 valency of the atoms was, no doubt, implied in 

 Gerhardt's theorv of types ; but it did not gain much 

 attention until later, when Frankland and Kolbt^ 



