Front Matter -- Third Report of the Committee on Photochemistry, National Research Council -- Experimental Technique in Photochemistry -- A Table of Quantum Yields in Experimental Photochemistry -- The Nature of the Primary Process in Photochemical Reactions -- Some Comparisons Between Photochemical Processes in Gases and Solutions -- The Mechanism of Aldehyde and Ketone Photolysis -- Hydrocarbon Free Radicals in Photoprocesses -- The Evaluation of Specific Reaction Rates in Chain Reactions -- The Secondary Processes in the Photodecomposition of Ammonia and Hydrazine -- Secondary Process in the Photochlorination of Carbon Monoxide and Hydrogen -- The Action of Optical Sensitizers on the Photographic Plate -- Photosynthesis.