400 TRANSACTIONS OF SECTION B. 



On the other hand, a strictly monomolecular reaction does not depend on the 

 collision of molecules. Hence the restraining influence of the increase of velocity 

 vanishes, and the increase of internal energy has its full effect, giving an abnormally 

 high temperature coeiiicient. The high values obtained for apparently monomole- 

 cular reactions may possibly be explained by supposing that vi^hen all the reacting 

 molecular species but one are present in large excess, that one will always find itself 

 within reach of a molecule of the other kind whether its velocity is large or small. 

 It may be remarked, however, that with the acid anhydrides, where the reaction is 

 with the solvent, the temperature coefficients are normal. Any general theory of the 

 temperature coefficients should be capable of explaining these facts. 



Professor B.vly said that during the last few years certain insight had been gained 

 into the phenomena of chemical reaction from absorption spectra observations. For 

 example, it had been shown four years ago that as a first step in a chemical reaction 

 the reacting compound is converted into an intermediate and highly reactive form. 

 It seems that the formation of the intermediate and reactive phase is a perfectly 

 general phenomenon and one that can be recognised as a fundamental step in any 

 chemical reaction whatever. The reactivity of a molecule is a minimum when that 

 molecule exists in the free state and in general before any molecule can enter into any 

 chemical reaction it must be converted into the active form. The conversion of the 

 inactive to the active form is accompanied by an absorption of energy which may be 

 taken up either from a solvent or as light or heat. According to the quantum theory 

 as originally formulated, this energy must be absorbed in quanta defined by hv where 

 h is the Planck constant and v the oscillation frequency of the radiant energy 

 absorbed. Based on this general theory the definition of a catalyst had been put 

 forward, namely, as an agent which tends to convert more of the reacting substances 

 into the reactive phase than would otherwise be formed. 



Professor Baly pointed out that Professor Lewis's theory of catalysis and reactivity 

 appeared to be a mathematical presentation of one single case of his own theory, 

 namely, that case in which the energy absorbed by the molecules had a wave-length 

 lying between 1|U, and 5/* in the short-wave infra-red region. Whereas his own theory 

 dealt with the possibility of the energy being absorbed at any vibration frequency 

 characteristic of the reacting substance. Professor Lewis only dealt with the special 

 case of short-wave infra-red radiation, and had shown that by the application of the 

 quantum theory to the Marcelin-Kice equation the increment of energy necessary to 

 convert a molecule into the active form given by yhv where y = 1,1, 3, &c., and is the 

 oscillation frequency in the short-wave infra-red region. Professor Lewis in this way 

 has extended the Einstein photochemical equivalent law to the infra-red, and it would 

 seem that as a result of the argument used by him a somewhat anomalous conclusion 

 is arrived at. The essential assumption underlying the Marcelin-Rice equation is 

 that a critical increment of energy must be given to a molecule in order to bring it 

 into the reactive condition, this increment being independent of the vibration 

 frequency. Professor Lewis stated that this critical increment may be one quantum 

 at the characteristic vibration frequency of the molecule. Now, the smaller the value 

 of the vibration frequency v, the smaller is the value of the energy quantum hv, and 

 therefore it follows from his argument that the actual or total amount of energy 

 necessary to bring a molecule into the active form is smaller, the smaller is the value 

 of V, i.e., the lower the temperature. 



On the other hand, the importance of the Marcelin-Rice equation cannot be denied, 

 and it is of considerable interest that recent work on the absorption spectra of organic 

 compounds had experimentally proved the existence of those very active phases of 

 molecules as intermediate stages in chemical reactions such as postulated byMarcelin. 

 Furthermore, in a recent experimental paper on photochemical reactions. Boll has 

 drawn exactly analogous conclusions as regards the existence of intermediate and 

 active phases of the reacting molecules. The formation of the intermediate and active 

 forms can readily be accounted for by assuming the existence of molecular force-fields 

 due to the iuxtaposition of the force-fields of the constituent atoms, these atomic 

 force-fields being electro-magnetic and previously postulated by Humphreys to explain 

 the Zeeman effect and the pressure shift of spectrum lines. The general bearing of 

 these force-fields on chemical reactivity need hardly be emphasised in a discussion on 

 catalysis, but the essential fact should be brought into prominence, namely, that 

 before a molecule can react it must first be converted into an active form by the 

 addition of energy, and that this energy can be absorbed at any vibration frequency 

 characteristic of the molecule. 



