Methods of hydrogenation. Catalyzers and their rôle in hydrogenation. Nickel carbonyl. The rare metals as catalyzers. The occlusion of hydrogen and the mechanism of hydrogen addition. The analytical constants of hydrogenated oils. Edible hydrogenated oils. Uses of hydrogenated oils and their utilization in soap making. Uses of hydrogenated oils and properties of certain hardened products. Hydrogenation practice. The hydrogenation of petroleum. The hydrogen problem in oil-hardening. Water gas as a source of hydrogen and the replacement of carbon monoxide bu hydrogen. Liquefaction and other methods for the removal of carbon monoxide. Hydrogen by the decomposition of hydrocarbons. Hydrogen by the action of steam on heated metals. Action of acids on metals. Miscellaneous methods of hydrogen generation. Hydrogen and oxygen by electrolysis of water. Precautions in handling hydrogen. Safety devices. Purification of gas.