Avogadro and Dalton: the standing in chemistry of their hypotheses / by Andrew N. Meldrum, D.SC ; with a preface by Francis R. Japp.

  • Andrew Norman Meldrum
Date:
1904
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Licence: In copyright

Credit: Avogadro and Dalton: the standing in chemistry of their hypotheses / by Andrew N. Meldrum, D.SC ; with a preface by Francis R. Japp. Source: Wellcome Collection.

Provider: This material has been provided by Royal College of Physicians, London. The original may be consulted at Royal College of Physicians, London.

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    Dalton. In the composite man of science, to whom Roscoe gives the name of Dalton, it is easy to discern the features of Charles, Gay-Lussac, and Lavoisier. Plainly, the effect of all this is to obscure the individuality of Dalton, and in his interests, therefore, to justify and make indispensable an impartial enquiry into his merits. Under the circumstances, it is not to be wondered at if the result of such an enquiry should be different from the customary estimate of Dalton. Dalton's contributions to chemical thinking may con- veniently be classified under the heads of law and theory. The experimental basis of Dalton's system of chemistry is to be found in the three laws of chemical combination by weight. Two of these laws, that of multiple and reciprocal proportion, necessarily involve, and depend upon, the law of constant proportion. The law of constant proportion was a burning question about the -beginning of the nineteenth century. Proust upheld the law against Berthollet. At the present day it is recop-nised that in the contentions of Berthollet there is much that is right. What we perhaps now are slow to recognise is how much the sound element in Berthollet's doctrine sustained the unsound. It is often now supposed that chemists were satisfied by 1806, cer- tainly by 1808, that Berthollet was wrong and Proust right. Thus Clarke says:— The memorable controversy between Proust and Berthollet had by this time [1808] exhausted its force, and nearly all chemists were satisfied that the law of definite or constant proportions must be true. ^ On the contrary, I suspect that in 1808, and even later, the currency of Berthollet's views was wider than Clarke thinks. Gay- Lussac in 1808 thought, with Berthollet, that the law of constant proportions held for gases, but, except in special cases, not for liquids and solids. Gay-Lussac indeed maintains that compounds are formed in variable proportions, unless these proportions are deter- mined by special circumstances. We must first of all admit, with M. Berthollet, that chemical action is exercised indefi- ' Clarke, The Atomic Theory, Manchester Memoirs, vol. 47 (1903), No. II, p. 9. H 1,
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