WATER CONTENT Fuel oil should not contain more than 2 per cent by volume of water and sediment. The method of determining the amount of water and sediment in fuel oil is as follows: "A definite volume of the oil sample should be thoroughly shaken or 'cut' with an equal volume of gasoline of a specific gravity not greater than 0.74, and centrifuged. An appropriate tube that goes with a special machine is commonly used for this purpose. (See fig. 10).b Centrifuging should be continued until there is a clear line of demarcation between the water and sediment and oil in the bottom of the tube, and until a constant reading of water and sediment is obtained. From this reading the percentage by volume of water and sediment is computed. If the oil under consideration has a specific gravity greater than 0.96 one volume of oil to three volumes of gasoline shOuld be used rather than equal volumes. When there is a question that the gasoline used for thinning the oil in making this determination renders insoluble certain of its fuel constituents, then mixtures of gasoline and carbon disulphide, or of gasoline and benzol may be used for "cutting," providing the specific gravity of such mixtures is not greater than 0.74. If., after continued centrifuging, a clear line
of demarcation between the impurities and the o:1 is not obtain able, the uppermost line should be read. If this procedure proves unsatisfactory, 100 C.C. of the sample may be distilled with an excess of hydrocarbons saturated with water and having boiling points slightly above and below that of water. Distillation is continued until all of the water has been distilled over into a graduated tube. The water in the oil is .thus distilled over and readily collects at the bottom of this tube, where the percentage may be read off. The percentage of sediment in the oil may then be determined on the sample remaining in the distilling flask by "cutting" it with gasoline and centrifuging. The percentage of water obtained in the tube added to the percentage of sediment gives' a total percentage to be deducted for moisture and impurities.