Desarrollo de la teoría de la disociación electrolítica

SV A N T E A R R H E N I U S

Development of the theory of electrolytic dissociation*
Nobel Lecture, December 11, 1903
At first sight nothing seems more obvious than that everything has a beginning and an end, and that everything can be subdivided into smaller parts. Nevertheless, for entirely speculative reasons the philosophers of Antiquity, especially the Stoics, concluded this concept tobe quite unnecessary. The prodigious development of physics has now reached the same conclusion as those philosophers, Empedocles and Democritus in particular, who lived around 500 B.C. and for whom even ancient man had a lively admiration. Empedocles taught that matter cannot originate from nothing and that matter cannot be destroyed. All happenings in the world are based on a change in form oron the combination or division of substances. Fire, air, water and earth are the four elements of which everything is composed. A continuous cycle is Nature’s chief characteristic. Democritus’ theories coincide even more closely with our modern views. He maintained that substances are composed of infinitely small, inseparable particles, which he called atoms. These vary in shape and size and yielddifferent products according to the differing ways in which they are combined together. This theory of the atoms was resuscitated by Gassendi in about 1650 and later adopted by Boyle and Newton. It attained its present great importance owing to Dalton’s discovery of the law ofmultiple proportions. For example, the various compounds of nitrogen and oxygen contain 0.57, 1.14, 1.72, 2.29 or 2.86parts by weight of oxygen per part by weight of nitrogen. There are no transitional forms between these compounds. To account for this phenomenon we assume, in common with Dalton, that the moleculus of the various nitrogen and oxygen compounds contain two atoms of nitrogen and 1, 2, 3, 4 or 5 oxygen atoms. This is specific to chemistry in contrast with physics where the simpler, continuous transitionfrom one state to another usually *This paper has previously been published in English in the Proceedings of the Royal Institution, 1904.

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1903 S.A.ARRHENIUS

applies. This dissimilarity between the two sister-sciences has frequently led to differences of opinion in physical chemistry. That discontinuous changes and multiple proportions also occur in physics has been assumed in manycases which, on closer examination, disproved this assumption. The law of multiple proportions is one of the foundations on which modern chemistry is built. Another such is Avogadro’s law which states that equal volumes of different gases at the same temperature and pressure contain the same number of molecules. This theory, which dates from the beginning of the nineteenth century, first met withstrong opposition and it was its great value in explaining the new discoveries within the rapidly expanding field of organic chemistry that resulted in its universal adoption in the middle of last century after Cannizzaro had acted vigorously in its favour. Meanwhile there were certain problems to be overcome before Avogadro’s law could be accepted. It was found, for example, that the molecularvolume of ammonium chloride, NH4Cl, in the gaseous state is greater than would be supposed on the basis of its chemical composition. This led to the assumption that the molecules of NH4Cl in the gaseous form are partly broken down into ammonia, NH2, and hydrochloric acid, HCl. Von Pebal and Von Than were able to prove that this does in fact occur. They used an apparatus shown in Fig. 1. Two tubes wereplaced one inside the other by means of a cork. The outer tube was sealed at its open end; the inner tube was open and contained at C, on top of an asbestos partition, a piece of NH4Cl. The top was heated in an air bath so that the piece of NH4Cl slowly volatilized. At the same time a stream of hydrogen was admitted through the two glass tubes D and E. Ammonia diffuses through porous walls at a...