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This method covers the determination of oily matter content of industrial waste water. N 1.—The Joint Committee on Uniformity of Methods of Water Examination has concluded that uniformity of methods for the determination of grease and oily matter is not practical on the basis of present technical knowledge. Commonly used solvents are hexane, petroleum ether, benzene, chloroform, or carbon tetrachloride. These solvents exert selective extraction of specific greases and oily constituents. In addition, nonoily materials, such as phenolic type material and colloidal sulfur, are selectively extracted to varying degrees by these solvents. The selectivity of extraction is affected by the sample-to-solvent ratio. Oily matter and grease may be of mineral, animal, or vegetable origin. The solvent action exerted on material of such different chemical structure will vary to a marked degree. Thus application of a test method for oily matter or grease to such materials will necessarily produce a variety of results depending on the solvent used. In one case, a solvent may be an excellent extractant of mineral oil and a poor extractant of vegetable oil. In another case, a second solvent may be a poor extractant for mineral oil but excellent for extracting vegetable oil. The definition of grease and oily matter by necessity is based on the procedure used because of the above considerations. The source of the grease or oily matter, the solvent used, the sample-to-solvent ratio, the pH of the sample, and the inclusion of nonoily matter will dictate the material determined and influence the interpretation of the results obtained.