342 SECTIONAL TRANSACTIONS.— B. 



The deduction from the purely spectral data of products of primary 

 dissociation is discussed, and attention is drawn to the ambiguities and 

 limitations of the interpretations already given. The necessary supple- 

 mentary evidence is indicated. 



The above considerations are carried over to the more general cases of 

 polyatomic molecules, with which photochemistry is mainly concerned. 

 The interpretations are applied to certain photodecompositions which have 

 recently been studied, such as the photolysis of metallic carbonyls, allyl 

 aldehyde, carbon suboxide, alkyl nitrites, metallic alkyls and others. 



Questions of a general nature bearing upon the above, such as energy 

 degradation within a molecule, reactions of low quantum yield, the signi- 

 ficance of different modes of induced molecular vibration, and the nature of 

 the products of primary one-act dissociation, are discussed. 



Dr. T. G. Pearson. — The photochemical generation of free radicals 

 (n.o). 



Dr. R. G. W. Norrish, F.R.S. — Photochemistry of polyatomic mole- 

 cules (11.30). 



Dr. H. W. Melville. — Secondary reactions in photo-chemistry (12.0). 



Nearly all photo-chemical reactions are complex, that is the primary 

 process — the absorption of a quantum of radiation — is succeeded by a series 

 of reactions which require separate investigation. This has been accom- 

 plished with a number of photo-reactions, for example, the photo-dissociation 

 of ammonia and the photo-synthesis of hydrogen bromide and the deviations 

 from the low photo-chemical equivalence explained. 



On the other hand when the primary process has been thoroughly 

 elucidated the photo-technique may be utilised to study the kinetics of 

 thermal reactions whose mechanism cannot otherwise be unambiguously 

 settled. Among the processes which may be studied in this way are the 

 rate of recombination of free atoms, the exchange reaction of deuterium 

 with hydrides, the thermal decomposition of polyatomic molecules, the 

 kinetics of the formation of substances of high molecular weight by poly- 

 merisation of simple molecules and the mechanism of slow and explosive 

 combustion. 



Afternoon. 



Dr. R. G. W. Norrish, F.R.S. , and Dr. H. W. Melville.— Experimental 

 demonstration illustrating the principles of photochemistry. 



Tuesday, September 15. 



Chemistry and Food Science : — 



Dr. L. H. Lampitt. — The scientific aspect of the preparation of food 

 (10.0). 



Dr. L. J. Harris. — The nutritional aspect (10.30). 



The final criterion by which the work of the food chemist must be judged 

 is Nutrition — does the food afford adequate nourishment ? Chemical 

 research has led to striking advances, such as are exemplified in the isolation, 



