Sperm oil has a standard weight established or recognized by the government, and according as varieties fall short or go beyond this measure, or standard, indicated by a nicely adjusted oilometer, its true weight and value are ascertained. Winter strained sperm oil is heavier, and burns away faster than spring strained sperm oil, for the simple reason that the winter oil is freer from spermaceti than the spring strained oil. Sperm oil is tested by authority of government, when contracts are made with the manufacturer to furnish oil for lighthouses, in the following manner: A common tin lamp of a cylindrical form is taken, and fitted with a wick which reaches to the bottom of the lamp. It is then filled with oil, and kept burning until all the oil in the lamp is burned up, and the wick so dry that not a drop of oil will fall from it. The number of hours which a given quantity of oil will burn, is another consideration included in determining the relative quality of oil. MIXING OR ADULTERATING OILS. Sperm oil is the purest and best of all varieties of whale oil, and brings the highest price in the market. Sperm oil is frequently mixed in greater or less proportions with right whale oil, which is an inferior kind of oil, and labelled _sperm oil_. This is a fraud, and it is practised more extensively than people are aware of. The fraud may be detected if either the right whale oil or sperm oil happens to differ in its shade or color, the one from the other. Sperm oil is lighter than right whale oil. If sperm oil is carefully put into a glass containing right whale oil, the former will not displace the latter, but remain separate; and the line of separation between the two kinds of oil, providing the color is somewhat different, may be easily detected. The smell and taste of oil, likewise, determine whether it be _bogus_ sperm oil or not. But the surest and most certain test of all others, as to the quality of oils, is by the oilometer,[K] (elaiometer.) This instrument is not only authorized by government, and employed for the purpose of securing genuine sperm oil, but it is used in all oil manufactories to determine both in buying and selling the different varieties of oils. It should be observed, however, that the mixing or adulteration of oils is never practised by the oil manufacturer. It would be fatal to his business if he should do it. There is no such article in an oil factory for sale as mixed or adulterated oils. It is either sperm or otherwise. The mixing takes place after it passes into the hands of the second, third, and it may be the fourth purchaser, or retailer. It is believed that but little genuine sperm oil reaches far back in the country, except, perhaps, for the purpose of lubrication in machinery; and even then, much of that, if tested by the proper measure, would probably be found badly mixed with an inferior quality of oil.