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catalysis. T e see in this volumc ideas based on kinetic and stat,istical theories, in militant juxta-position to those which have their origin in the theory of electrolytes and in the structural conceptions of organic chemistry. Also in some papers there can be perceived an inclination to explain the phenomena of catalysis in terms of thermodynamic conceptions. It is too much to expect that these ideas will be fused into one comprehensive theory as a result of the discussion, for each viewpoint has been gained as a result of experience in specialised fields of chemistry, each of which requires for its development a specialised theory. However, the discussion should serve the useful purpose of breaking down whatever isolation exists between workers in different fields. The kinetic and statistical aspect of catalysis is treated in papers by Hinshelwood, Rideal, Polanyi, Christiansen, and Backstrom. This section of the discussion shows the wide range of applicability of the Christiansen theory of chain-reactions to the explanation of positive and negative catalysis, and to the explanation of the effects of inert gases on the velocity of chemical change. Backstrom employs this theory to explain the inhibition of auto-oxidation of organic compounds in aqueous solution, and Polanyi applies it to the explanation of the inhibition of chain-reactions in gases by bromine. The work of Semenoff shows how useful is this theory in the treatment of the phenomena arcompanying the inception of flame in a gaseous mixture. -1paper by Hinshelwood on the influence of nitrogen peroxide on the union of hydrogen and oxygen sets forth an interesting case of trace catalysis. Papers by Boeseken, by Rice and Sullivan, and by hIoureu are concerned with catalysis in reactions in organic chemistry. Moureu shows that anti- or pro- oxygenic catalysis occurs in a large number of cases of oxidation, and to explain their action, puts forward an intermediate compound theory of catalysis. Boeseken advances the view that dislocation of chemical linkings by a catalyst is the cause of changes in the velocity of reaction and discusses the effect of the catalyst on the constants in the Arrhenius relation, logek = --A/RT = B. Kendall and Harrison discuss the evidence for compound formation in the ester-water system. I n the introductory paper to the discussion, Lowry points out the necessity for agreement bn the main features of the catalysis by acids and bases, and in particular, recognition of catalysis by neutral salts. Bronsted, Damon, v. Euler, Harned and Akerlof, Low-ry and IVilson, and Skrabal contributed papers to this section, and Lapworth, hlcBain, Giordani and others to the discussion. There was general agreement as to the impossibility of explaining the so-called acid and basic catalysis solely in terms of the concentration of hydrogen and hydrogen ions, but there was great divergence in the methods adopted in explaining the abnormalities. The catalytic effects of ions other than hydrogen and hydroxyl and even of neutral molecules was admitted, and Bronsted. in order to group all of the catalysis as acids or bases, puts forward a new theory of acids and bases. There was less agreement with regard to the explanation of the effect of concentration of electrolyte on the catalytic phenomena. There is a.,disinclination in some quarters to admit the usefulness of the Debye-Huckel theory in the explanation of these effects. There was agreement as to the main facts, however. If the velocity of catalysis by an acid H h is given by I'
=
kh[Hf]
+ ka[.l-] + k,,[HAI,
then it is recognised that the coefficients, k h , k a r kn, and the equilibrium constant K H . ~ are changed on the addition of electrolytes, either by an effect on the medium, or on the ionic hydration. The regularities observed in the salt effects are illustrated by a large amount of experimental data. lt'. E. Garner
ERRATUM In Fig. 2 on p 6 of the article by Xessrs. Ferguson and Funnell, change F and W, ITr., and B and 1%' to F and F, Wr., and B and B.
