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

  • Meldrum, Andrew Norman, 1876-1934.
Date:
1904
Catalogue details

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.

    9/124
    PREFACE. The important queslioii whether, in discussing the constitution of matter, the atom or the molecule should be first considered, is one regarding which there has been considerable dilTerence of opinion among chemists. Formerly, few would have disputed the claim of the atom to l)iior consideration. Not only did Dalton's atomic hypothesis precede Avogadro's molecular hypothesis in order of time, but this chronological order seemed also to be the natural order, involving, as it did, only the usual transition from the simpler to the more complex conception. But the history of the science shows that, enormous as were the services which Dalton's atomic hypothesis rendered to chemistry, the chief object of that hypothesis—the determination of a set of consistent atomic weights—remained for a long time merely a pious hope. Avogadro's rule supplied a means of determining the molecular weights of substances, and, from these molecular weights, of ascertaining which of several possible atomic weights of a contained element was the correct one. Until this step had been taken, the marvellous developments of theoretical chemistry which have characterised the last fifty years would have been impossible. In the study of the constitution of matter, therefore, we are compelled, by the very nature of the particular problems of scientific measurement and calculation involved, to reverse what is apparently the natural order of things and to proceed from the more complex to the simpler—from highly complex objects of sense to successively simpler and simpler conceptual structures underlying these. Thus the order of quantitative determination is :—(i) relative weights of comparable amounts of matter in hulk (gaseous or dissolved); (2) relative weights of molecules; (3) relative weights of atoms; and (4), if subsequent experiment should justify the most recent speculations, mass of electrons. The view here stated as to the true ratiocinative order of precedence of the molecular and atomic hypotheses has been held by various chemists; but I have nowhere else seen it expounded with such wealth of illustration and with so exhaustive a knowledge of the fundamental literature of the subject, as in the present monograph by Dr. Meldrum. Francis R. Japp. University ok Aiierdeen, September, 1904,