ON ABSORPTION SPECTRA OF ORGANIC COMPOUNDS. 309 



is thus entirely due to the different phases they exist in, and lias nothing to 

 do witii the bond between the two central carbon atoms, which is the same 

 in both compounds. If the two compounds existed in the same phase, the same 

 amount of energy would dissociate them both. 



Pari II. 



In this section a brief account may be given of the application of molecular 

 phases to chemical reactions, for it can be shown that their existence receives 

 thereby very strong support. Although, perhaps, the connection between this 

 application and absorption spectra might at first sight appear to be only indirect, 

 yet it is self-evident that if the proof of the existence of molecular phases 

 depended on absorption-spectra observation-; alone the arguments in their favour 

 would be less convincing. Since the existence of these phases is founded 

 on the reactivity of elementary atoms expressed on a quantitative basis, their 

 failure to give a quantitative basis to the reactions of molecules would militate 

 strongly against their reality. It must be admitted, even by the most sceptical, 

 that any corroborative evidence in their favour, even if such evidence have no 

 immediately apparent bearing on absorption spectra, must materially strengthen 

 those arguments which were based on absorption spectra alone. 



As was explained in the preceding section, the affinity of atoms for one 

 another, which causes them to combine with the loss of whole numbers of their 

 atomic quanta of energy, is due to the electromagnetic fields of the atoms. 

 The resulting freshly synthesised molecule is in a metastable state, since each of 

 its component atoms possesses an external force field, and condensation between 

 these fields must ensue with the loss of a definite number of molecular quanta 

 and the formation of a molecular phase, each possible phase being defined by 

 the number of molecular quanta that have been lost in its formation. It follows 

 from this that the condition of the molecular force field must be different in 

 each phase of a given molecule, and, since the reactivity of a molecule must 

 depend on its atfinity and power of attracting other molecules, the reactivity 

 of each phase of a given molecule must be different. There is a great mass of 

 evidence which establishes this difference in reactivity between the various 

 phases of a given molecule, and which will be discussed in this section. A 

 typical instance may be mentioned here — namely, that of benzaldehyde — which 

 exhibits entirely different absorption spectra when in solution in alcohol and 

 in strong sulphuric acid, and therefore exists in different phases in these two 

 solvents. When in alcoholic solution benzaldehyde is readily oxidised by atmo-. 

 spheric oxygen, and suffers no change when the solution is warmed after the 

 addition of a little sulphuric acid. On the other hand, in strong sulphuric 

 acid solution benzaldehyde is unaffected by atmospheric oxygen and is readily 

 sulphonated. 



Since the reactivity of its different phases is different, it is necessary to bring 

 a molecule into the correct phase before it can enter into a specific reaction. 

 Almost without exception molecules when in the free state exist in non-reactive 

 pha.=es — that is to say, phases of too small energy content — and it is therefore 

 necessary to supply energy to them in order to induce the necessary change in 

 phase before the reaction will take place. It is a well-known fact that sub- 

 stances in the free state will not react together, even though the reaction when 

 it does take place may be highly exothermic. Hydrogen and oxygen, hydrogen 

 and chlorine, hydrogen chloride and ammonia, are instances which are familiar 

 to everyone, and it is equally well known that if energy is supplied to these 

 pairs of substances the reaction commences at once, this being due to the phase 

 change which is produced by the energy supplied. 



The difference in energy content of any two consecutive phases of a given 

 molecule is one molecular quantum, and consequently the amount of energy 

 required to convert a molecule from a non-reactive phase to a reactive phase 

 must be 1, 2, 3, or 4 etc. molecular quanta depending on the relation between 

 the two phases. This process will form the first stage of every reaction. When 

 the phase change has taken place the molecule will react, one or more new 

 molecules being produced. In this process, which is the second stage of the 

 reaction, energy is lost, since otherwise the process would not take place. Each 

 molecule formed in this second stage will be in flir freshly synthesised state, 



