The development of the atomic theory.

  • Andrew Norman Meldrum
Date:
[1910-1911]
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Licence: In copyright

Credit: The development of the atomic theory. Source: Wellcome Collection.

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    and E. von Meyer19 in 1807. A. Wurtz, putting the date even earlier, says “the truth of the fixity of chemical proportion was definitely established in the year i8o6.’’3,> These writers do not adduce any evidence in support of their statements. They seem to consider their case so probable that proof is unnecessary. On the contrary their case is not even probable. It depends on a fatal under- estimate of the influence of Berthollet. He occupied a commanding position in the world of science, so that his ideas could not fail to receive consideration in full. Not only were his main ideas of the highest intrinsic value but his teaching on the very subject of constant proportion, in the light of the knowledge which was then available, was extremely plausible. There are two reasons for this. First, chemists in the XVIIIth century had concentrated their attention on the outstanding compound of each pair of elements, and on this insufficient basis the doctrine of constant composition had been founded. Berthollet raised a new problem by studying the relation between the different compounds of the same elements. It has already been suggested that his teaching did not so much contradict Lavoisier’s and Wenzel’s and Richter’s as go beyond it. While holding in general that affinity tends to unite substances in all proportions, he pointed out that this tendency could be limited by physical factors such as cohesion and insolubility and elasticity, in which case the compounds would be produced on which the supposition of fixed proportion had been based. In the second place the wretched state of chemical analysis only too easily afforded data in support of variable proportion. Berthollet’s theory suited the exis- tence of discordant analyses of the same substance by 19 “Hist, of Chem.,” Erg. trans., p. 194, 1906. 20 The Atomic Theory,” Eng. trans., p. 9, 1880.
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