Triumphs and wonders of the 19th century, the true mirror of a phenomenal era, a volume of original, entertaining and instructive historic and descriptive writings, showing the many and marvellous achievements which distinguish an hundred years of material, intellectual, social and moral progress .. . and thus this most fruitful idea, designated as isomerism, wasintroduced into the science. The next great step was the introduction of the theory of radicles, firstsuggested tentatively by Berzelius (1810), but put forward in a definite wayas one of the results of the classical investigation on b
Triumphs and wonders of the 19th century, the true mirror of a phenomenal era, a volume of original, entertaining and instructive historic and descriptive writings, showing the many and marvellous achievements which distinguish an hundred years of material, intellectual, social and moral progress .. . and thus this most fruitful idea, designated as isomerism, wasintroduced into the science. The next great step was the introduction of the theory of radicles, firstsuggested tentatively by Berzelius (1810), but put forward in a definite wayas one of the results of the classical investigation on benzoyl by Liebigand Wohler (1832). That is to say, a group of elements, or radicle, canpass through a series of compounds, from one to the other, as though thegroup were one single element. For years this idea was the guiding prin-ciple in chemical investigations, and was most useful in aiding the classifica-tion of chemical compounds and bringing order out of the chaos of accumu-lating observations. But the search for radicles was in a sense a vain one. We now know thatno radicle exists as such by itself. Meanwhile. Dumas and his pupil Laurent,had introduced and developed the theory of types, whereby all chemical com-pounds could be classified under four types, which marked a distinct step in. MICHAEL FAHADAY, 198 TRIUMPHS AND WONDERS OF THE XIXth CENTURY advance. Laurent, together with his colleague G-erhardt (1816-1856), recog-nized the shortcomings of both the radicle and type theories in their earlierforms, and showed their inter-relation, when modified so as to do away withcertain inconsistencies. Dumas had before this demonstrated the theory of substitution (1834), —that is, that in certain compounds one or more of the elements can be drivenout and replaced by others without changing the essential characteristics ofthe compound. For instance, chloracetic acid, in which part of the hydrogenof acetic acid has been replaced by chlorine, contains all the essential charac-t
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