_Decomposition of Fats by Bacteria._--Though this subject is not of any practical interest in the preparation of fatty acids for soap-making, it may be mentioned, in passing, that some bacteria readily hydrolyse fats. Schriber (_Arch. f. Hyg._, 41, 328-347) has shown that in the presence of air many bacteria promote hydrolysis, under favourable conditions as to temperature and access of oxygen, the process going beyond the simple splitting up into fatty acid and glycerol, carbon dioxide and water being formed. Under anaerobic conditions, however, only a slight primary hydrolysis was found to take place, though according to Rideal (_Journ. Soc. Chem. Ind._, 1903, 69) there is a distinct increase in the amount of free fatty acids in a sewage after passage through a septic tank. Experiments have also been made on this subject by Rahn (_Centralb. Bakteriol_, 1905, 422), who finds that _Penicillium glaucum_ and other penicillia have considerable action on fats, attacking the glycerol and lower fatty acids, though not oleic acid. A motile bacillus, producing a green fluorescent colouring matter, but not identified, had a marked hydrolytic action and decomposed oleic acid. The name "lipobacter" has been proposed by De Kruyff for bacteria which hydrolyse fats. III. _Use of Chemical Reagents._--Among the chief accelerators employed in the hydrolysis of oils are sulphuric acid and Twitchell's reagent (benzene- or naphthalene-stearosulphonic acid), while experiments have also been made with hydrochloric acid (_Journ. Soc. Chem. Ind._, 1903, 67) with fairly satisfactory results, and the use of sulphurous acid, or an alkaline bisulphite as catalyst, has been patented in Germany. To this class belong also the bases, lime, magnesia, zinc oxide, ammonia, soda and potash, though these latter substances differ from the former in that they subsequently combine with the fatty acids liberated to form soaps.