According to Berthelot and Gaudechon,1 ethyl alcohol in absence of air is not decomposed by sunlight (of wave-length greater than 0.3µ). It is, however, photolysed by the direct rays of a mercury vapour lamp, used without any interposed screen. The decomposition is primarily into acetaldehyde and hydrogen, but usually there is some further photolysis of the aldehyde into carbon monoxide and ethane. When water is present, the reactions are substantially the same, but with a tendency to form acid products.