May. 28, 1903] 



NATURE 



83 



facts from the theoretical language in which he clothed 

 them. But we may say, broadly speaking, that 

 Dalton's atomic theory led to the establishment of three 

 fundamental laws of chemistry, the law of definite 

 proportions,^ the law of multiple proportions (which 

 really includes the law of definite proportion) and 

 the law of equivalents. The fact that elements unite 

 in more than one ratio by weight obviously made 

 further assumptions necessary, over and above the 

 atomic hypothesis, before any table could be drawn up 

 of relative atomic weights. Dalton seemed to have 

 felt no hesitation in making the assumptions that 

 seemed to him convenient (" New System," part i. p. 

 214). But Wollaston, while giving Dalton's theory 

 his powerful support, showed, in 1814, that Dalton's 

 assumptions were arbitrary, and Wollaston 's term 

 "equivalent," which was regarded as implying no 

 hypothesis, soon became a serious rival to the term 

 "atomic weight." Davy, to whom (with Henry) 

 Dalton had dedicated part ii. of the " New System " in 

 18 10, gave Dalton's views a reception more than cool.^ 

 Among the great chemists of the day, it was to Berze- 

 lius, who had already been trying to extend the quantita- 

 tive work of RIchter, that Dalton 's views appealed most. 

 But Berzelius, less imaginative, but more critical a 

 thinker and more accurate a worker, than Dalton, saw 

 that much remained to be done before the theory could 

 be placed on a satisfactory basis. " I think," he writes 

 to Dalton, " that we must let experiment mature the 

 theor}-. " Berzelius's admirable " Essai sur les Pro- 

 portions chlmiques " of iSig'* gives the first critical ac- 

 count of the atomic theory, while the experiments re- 

 corded therein may be regarded as having first placed 

 the laws of multiple proportions and of equivalents on 

 a sufficiently wide basis to be regarded as generally 

 valid. 



Nevertheless, the conviction that chemistry could 

 do quite well without the conception of atoms, and that 

 the notion of " equivalents " was sufficient, grew 

 steadily; between 1840 and 1850 Leopold Gmelin's 

 system of equivalents came to be accepted almost uni- 

 versally.* It was the growth of organic chemistry and 

 the confusions in organic chemistry which the '* equi- 

 valent " conception was powerless to remove that re- 

 stored the notion of the atom. From 1842 onwards 

 Laurent and Gerhardt, those two Ishmaels of their 

 day, fought Indefatlgably for the establishment of some 

 consistent theory of organic compounds ; and they 

 reached consistency only by reviving the simple mole- 

 cular hypothesis of Avogadro and Ampere.* This hypo- 

 thesis gave them at once an experimental method for 

 the determination of the relative molecular weights of 

 all volatile compounds ; and It gave them simultaneously 

 a method for determining maximum values for 

 the atomic weights of the elements therein contained, 

 for obviously each molecule must contain at least one 

 atom. But neither they, nor Cannizzaro later, were 

 able to give any simple rule applicable in all cases to 

 the determination of atomic weights. The atomic 

 weight of carbon on which the reform of Laurent and 

 Gerhardt pivoted was an exception to the rule of 

 Dulong and Petit on which Cannizzaro, with general 

 approval, has laid so much stress. But a hypothesis 

 may be useful without being perfect. The atomic 

 hypothesis in the hands of VVurtz, Hofmann, William- 

 son, Frankland, Kekul^, and Baeyer, and with the 

 most brilliant and essentia) but involuntary help of 



J The present writer has briefly discussed the history of this law in 

 Nature, vol. 1. 1894, p. 149. ' 



^^■}^ 'T° unaPPreciative lines in a footnote to the "Elements of Chemical 

 Philosophy, published in 1812 (ste p. 78 tf the edition of i860). 



■• The Swedish edition appe.-ired earlier. 



■» Gmelin himself in his " Handbook of Chemistry" inclined to the atomic 

 theory. English edition, translated by H. Watts, vol. i. p. 42. 



s " Equal volumes of all gases under the same conditions of temperature 

 and pressure contain equal numbers of molecules.' 



NO. 1752, VOL. 68] 



Berthelot and of Kolbe, was the instrument which served 

 to build up modern organic chemistry. It gave 

 chemists an unforeseen mastery over the elements ; the 

 synthesis not only of the natural organic compounds, 

 but of an infinity of new ones seemed to be brought 

 within their reach. In this development Manchester 

 had again played a part of first-rate importance. Frank- 

 land's theory of valency was based on his researches on 

 the organometalllc bodies carried out in the Owens 

 College, where he was professor, and published in 

 1852. The exact rdle of F"rankland's work on valency 

 (neglected at first by most chemists) was this : it forced 

 his friend and fellow worker, Kolbe, to abandon the 

 Berzelius copula theory, and led him to build up " con- 

 stitutional " formulae for the chief alkyl compounds 

 so near our own that he was enabled to predict from 

 them the existence of secondary and tertiary alcohols. 

 The formulae of Kolbe, with the atomic weights of Ger- 

 hardt, again led inevitably to the great theories of 

 Kekul^ on the tetravalency of carbon and the linking 

 of the atoms, which are now regarded as fundamental 

 in organic chemistry. 



In 1875, 



horizons were brought into view. 



Wollaston predicted of Dalton's atoms in 1808 that 

 " the arithmetical relation alone will not be sufticient 

 to explain their mutual action, and that we shall be 

 obliged to acquire a geometrical conception of their 

 relative arrangement in all the three dimensions of 

 solid extension." Le Bel and van 't Hoff, by their 

 work on the " asymmetric " carbon atom, created a 

 new " chemistry in space," of which one Of the most 

 striking results has been the beautiful synthesis of the 

 sugars, by Emil Fischer and his fellow workers. 

 Prof. Pope has recently extended these new ideas 

 to inorganic chemistry with brilliant results. 



But such exceptional results as those of Prof. 

 Pope bring sharply into view the fact that the direct 

 service of the atomic theory to inorganic chemistry 

 has been relatively small. What, for instance, has the 

 theory of valency to tell us about such a series of corn- 

 pounds as the tungsten chlorides discovered by 

 Roscoe? But if the atomic theory has helped us com- 

 paratively little in determining the constitution of in- 

 organic compounds, 1 it has contributed to our discovery 

 of new inorganic elements. The attribution of certain 

 numbers, equivalents or atomic weights, to the ele- 

 ments led naturally to speculation on mathematical 

 relationships between them. Many of these specula- 

 tions, like the original one of Prout in 1815, and that 

 of Dr. Henry Wilde, of Manchester, more recently, 

 were suggested by the fascinating question of the funda- 

 mental unity of all matter. Are the elements really com- 

 pounds of one original matter — the protyle of the Greeks 

 revived by Prout and by Sir W. Crookes? If so the 

 atomic weights must have some common measure. On 

 the accurate determination of atomic weights, made 

 largely to settle this question, infinite pains have been 

 spent by Stas, Marignac, Richards, and many others. 

 On the criticism and accurate calculation of results from 

 these experimental determinations infinite pains have 

 again been spent, by Meyer and Seubert, and above all 

 by Prof. F. W. Clarke, who delivered the Wilde lecture 

 of the Manchester Literary and Philosophical Society 

 at the centenary celebrations last week. 



But though certain numerical relations seem strik- 

 ing, chemists are certainly as a body not inclined to 

 acknowledge the existence of any, exact forrhula e.x- 

 pressing as a mathematical series the series of the 

 atomic weights. 



More immediately fruitful of results have been 

 speculations less 'fundamentally ambitious. The 

 schemes of Lothar Meyer and MendeleefT, according 



1 The researches of Divers and of Raschig on certain sulphur and 

 nitrogen compounds may be regarded as examples of what may be done in 

 this direction.' 



