414 



SCIENTIFIC THOUGHT. 



the " atomicity " or " valency " of chemical substances 

 be they elements or compounds. This most recent de- 

 velopment of chemical systematisation originated in Eng- 

 land, 1 whereas the " radicle " theory belonged more to the 



the view that an understanding of 

 chemical reactions must ultimately 

 depend upon a study of the nature 

 and degree of chemical affinity, and 

 maintained that so far the connec- 

 tion of chemical with electrolytic 

 phenomena afforded the only clue 

 to the comprehension of the nature 

 of chemical affinity. The atomic 

 theory had now absorbed all in- 

 terest, to the detriment of a physi- 

 cal theory of chemical affinity such 

 as Berthollet had attempted. It 

 was held that by ignoring the 

 electro - chemical differences, the 

 " modern '' school lost the only re- 

 maining chance of explaining, and 

 not merely classifying, chemical phe- 

 nomena. A good exposition of the 

 latter argument will be found in 

 A. Rau, 'Die Theorien der moder- 

 nen Chemie.' 



1 The number is small of the Eng- 

 lish names which about the middle 

 of this century figured prominently 

 in the discussions by which, in the 

 German and French annals of 

 science, correcter views on the con- 

 stitution of chemical compounds 

 were gradually elaborated. Kane's 

 work was overlooked, but William- 

 son, Odling, and Frankland have 

 had a very marked influence ; and, 

 as in so many other sciences, pioneer 

 work in modern chemistry was done 

 in this country, notably by Frank- 

 land. Liebig, after his visit to 

 England in 1837, wrote to Wonler : 

 li I have traversed England, Ireland, 

 and Scotland in all directions, have 

 seen much that is astonishing, but 

 have learnt little : whence is scien- 

 tific knowledge to come in England, 

 as the teachers are so inferior '' 

 Among older men, Thomson is still 

 the _best; among younger men, 



Graham : modest and unassuming, 

 he makes the most beautiful dis- 

 coveries. Nevertheless, a splendid 

 nation," &c. &c. ('Liebig's und 

 Wohler's Briefwechsel,' vol. i. p. 

 113.) From what I stated above 

 (chapter iii. p. 296, &c.), we are, 

 however, quite prepared to find 

 that the idea which more than any 

 other has brought some order and 

 system into modern chemical theory, 

 and which has united the diverg- 

 ing currents of the foreign schools, 

 has come from England. Frank- 

 land more than any other must 

 be looked upon as the origina- 

 tor of the modern theory of the 

 atomicity or valency of chemical 

 elements and compounds. The 

 history of this conception can be 

 well studied in the collection of 

 scientific papers which he published 

 with valuable introductions in 1877 

 (' Experimental Researches in Pure, 

 Applied, and Physical Chemistry,' 

 London, van Voorst). His re- 

 searches commenced in those years 

 when great confusion existed in or- 

 ganic chemistry, "when the wildest 

 theories of the constitution of or- 

 ganic compounds created but little 

 surprise ; the assertion, for instance, 

 that an atom of carbon was united 

 with four atoms of hydrogen and 

 two of chlorine would scarcely have 

 been considered intrinsically impro- 

 bable, and certainly not impossible " 

 (loc. cit., p. 26). The idea existed 

 that bodies could enter into combin- 

 ation with other bodies, notably or- 

 ganic radicles, and could still retain 

 in such combination their original 

 affinities unimpaired ; a new term, 

 that of "conjugate," "copulated," 

 or " paired " compounds, had been 

 invented and adopted by Berzelius. 



