if 



660 



REPORT — lb84. 





'111 



I 



-;!J 



called substitution theory. Dumns, to ■\vliom we owe this tliporv, sliowed that 

 chlorine can take the place of hydro^'eii in many compounds, and that the result iutr 

 body possesses characters similar to the ovi^rinal. ]5crzelius opposed this viow, in- 

 sistinp: that tlie essential diflerences lietwciMi these two elements rendered the idea 

 of a substitution impossible, and notwitiistandin!,' the ])owerfid advocacy of Lii-bij:, 

 and the discovery by ^leisiMis of rever,-e -uhstitutions (tliat is the rc-rormatioii ol' 

 the original compound from its substitution-product), J'er/elius rmiained to tho 

 end unconvinced, aUd tluit wliich was in vality a contlrmation of liis own theory 

 of compound radicals, which, as Liebiy: s;iys, ' illumined many a dark chapter iii 

 organic chemistry,' was looked upon by liini as an error of the deepest dye. Tlii-t 

 inability of many minds to st>e in the discoveries of others confirmation of their 

 own views is not imcommnii ; thus IJalton, we may remember, couhl never liriiiu' 

 himself to admit the truth of (iay-TiU<sae".s laws of jiaseous volume-combination, 

 althou<rh, as JJerzelius very truly sa\s, if we write atuin for vuliimc aiul consider 

 tho substance in the tolid state in place of the state of gas, the discovery of 

 Gay-Lussac is sei'n to be one of the most jiowerful arguments in favouv (>f 

 Dalton'a hypothesis. 



But thei(! isanollicr chaiigi' of vii'W,(uit!nii' from the commencement of ilu'Dum^.i 

 epoch, which has exerted an iutluence ofpial, if not superior, to those already named 

 on the progress of our science. Tho relative weights of the ultimate particles, to 

 use Dalton's own words, which up to this time ha<l been generally adopted hv 

 chemists, were tho equivalent weights of Dallon and Wollaston, re])resenling, in 

 the case of oxygen and hydrogen, the proportions in which these elements com- 

 bine, viz., as iS to 1. 'J'he great ywedish chemist at this time stood almost alone 

 in supporting another hypothesis ; for, founding his arg-ument on the simple laws of 

 ■volume-combination enunciated by Gay-Ijussac, he asserted that the true atomic 

 weights are to lie represented hy thi> relations existing between equal vcdunies o? 

 the two gas •«, viz,, as lOtol. Still these views found no favour in the eyes of 

 chemi.sts until (xerhardt, in L"^!.'), proposed to doulde the equivalent weights of 

 oxygen, suljihur, and carbon, and then the opposition wdiieh this suggestion met 

 with was most intense, Berzeliiis himself not ev(Mi deig'uing to mention it in his 

 annual account of tho progress of the science, thus proving the truth of his own 

 words: 'Thattoliold an opinion haliitually often leads to such an absolute con- 

 viction of its truth that its weak points are unregarded, and all proofs against it 

 ignored.' Nor were these views generally adopted by chemists until (!annixari>, 

 in 18'!58, placed tho whole subject on its present firm basis by clearly distingui>!iir.g 

 between equivalent and molecular weigiits, showing how the atomic weights of tho 

 constituent element.s are derived from the molecular weights of their volatile com- 

 pounds based upon the law of Avogadro and Ampere, or where, as is the ca^e 

 with many metals, no compounds of known vapour-density exist, how the same 

 result mav be ascertained by the help of the specific heat of the element itsell'. 

 llemarkablo as it may appear, it is nevertheless true th.at it is in the country of 

 their birth thatGerhardt's atomic weights and the consequent atomic nomenclatiiro 

 have met with most opposition, so much so that within a year or two of the present 

 time there was not a single course of lectures delivered in Paris in which these 

 were used. 



The theory of organic radicals, developed by liebig so long ago as 1834, 

 received numerous experimental confirmations in succeeding years, Bunsen's 

 classical research on cacodyl, proving the possibility of tho existence of metallo- 

 organic radicals capable of playing the part of a metal, and the isolation of the 

 hydrocarbon ethyl by Frankland in 1S40, laid Avhat tho supporters of the theory 

 deemed tbe final stone in the structure. 



The fusion of the radical and type theories, chiefly effected by the discovery in 

 1849 of the compound ammonias by Wurtz, brings us to the dawn of raodera 

 chemistry. Henceforward organic compounds were seen to be capable of compari- 

 son with simple inorganic bodies, and hydrogen not only capable of replacement 

 by chlorine, or by a metal, but by an organic group or radical. 



To this period my memory takes me back. IJebig at Giessen, Wiihler in Got- 

 tingen, Bunsen in Marburg, Uumas,Wurtz, and Laurent and Gerhardt in Paris, were 



