adhesiveness. The fluidity of an oil is thus to a large extent a measure of its value." We may, therefore, conclude that the oil which combines in itself the greatest fluidity with the most "staying" property, that is, of adhering to the journal, is the best oil.

Besides these, manufacturers who are close observers, have a variety of simpler tests, such as timing a ball falling through an oil column of known height; rubbing a portion of the oil between the thumb and forefinger; letting drops of the oil fall upon the surface of the same oil in bulk; exposing the oil for a few hours, or a day, upon the surface of a piece of glass. These tests (except the first) are not accurate, and oils are not bought or sold upon their indications.

IV. THE COMPOSITION OF OILS AND THEIR FREEDOM FROM ADMIXTURE WITH OTHER OILS OR FOREIGN SUBSTANCES.

It is absolutely essential that a dealer should have placed before him some reliable and easily-applied tests of the purity of the oils he is accustomed to handle. It is to be understood, however, that all mixtures of oil are not fraudulent combinations; such mixtures are continually made and sold for special purposes; notwithstanding this, when a mixture of 5 per cent. of sperm oil and 95 per cent. of "neutral" mineral oil can be sold for pure sperm, it is very desirable to know just what such a mixture is made of. The tests which are applicable here, are partly chemical and partly mechanical. We will consider first those

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which belong to the domain of chemistry, and propose to confine our remarks exclusively to the detection of admixtures with petroleum oils. The consideration of combinations of animal or vegetable oils, containing no petroleum, does not come within the scope of this volume. The outlines of the process for the detection of a mixture of petroleum and other oils will be found in the examination of the density; a lower flashing or burning point, would indicate the presence of a mineral oil. Fluorescence would positively betray petroleum. Finally, the incomplete saponification of the sample would be conclusive. The following method of conducting this strictly chemical test is taken from a paper by Mr. Alfred H. Allen, published in the Oil and Drug Reporter,' October 18, 1881.

"The best and most accurate method of detecting hydrocarbon oils in, and quantitatively separating them from, fat oils, is to saponify the samples and then agitate the aqueous solution of the soap with ether; or by separating the ethereal layer and evaporating it at, or below, a steam heat, the hydro-carbon oil is recovered in a state of purity. Either caustic potash or soda may be employed for the saponification, but the former alkali is preferable, owing to its greater solubility in alcohol and the more soluble character of the soaps formed. A convenient proportion to work with consists of 5 grms. of the sample of the oil and 25 c.c. of a solution of caustic potash in methylated spirit, containing about 80 grms. of KHO per liter. Complete saponification may usually be effected by boiling down the mixture in a porcelain dish, with frequent stirring until it

froths strongly. After evaporating off the alcohol, the soap is dissolved in water and agitated with ether. The ethereal solution is separated, washed in a little water and carefully evaporated. The agitation with ether must be repeated several times to effect a complete extraction of the hydro-carbon oil from the soap solution."

The foregoing process has been proved to be accurate on numerous mixtures of fat oils with hydro-carbon oils. Sperm oils and spermaceti, however, are remarkable exceptions, as neither of these is wholly saponifiable. The following table, furnished by Mr. Allen, gives the result of his experiments with this test.

The mechanical tests referred to include filtration for the separation of foreign matter, and the critical tests for fluorescence.

Petroleum, either crude or refined, when perfectly free from admixture of any kind, is highly refractive of light, and presents a brilliant lustre.

In the crude state, it is usually too opaque to be tested by transmitted light except in very small quantities or in thin layers, as when spread upon a polished surface of glass; a very small percentage of water dims its appearance. This is readily shown by heating a portion of the oil, when frothing takes place upon the surface and continues until the last trace of moisture is expelled.

Fluorescence, a remarkable peculiarity of petroleum oils, for some reason which we cannot appreciate, is considered an objectionable feature. I know of no reason why it should be so considered, or why so many methods are contrived to destroy it, excepting that petroleum is so often employed as an adulterant to more expensive oils, on which account it is desirable to remove so persistent a quality. In most cases it is evident upon first sight. The least trace of fluorescence is rendered apparent by pouring a small portion of the oil upon a polished plate of black glass, or upon a piece of glass thickly coated upon one side with black paint. The film of oil spreads itself upon the surface of the glass, and as this is turned at different angles to reflect the light properly, the fluorescence, if any, is plainly shown.

V. ITS NATURAL COMPOSITION BY ACTUAL ASSAY.

This test provides for the detection, not of foreign admixtures, but for fraudulent combinations of petroleums of different gravities and inferior qualities, and is applicable to both crude and refined oils. It is quite possible to so combine portions of residuum, paraffine oil, and benzene, that it would be difficult to detect a fraudulent mixture without this process. It might possess all the usual appearances of natural crude oil, as to color, odor, and gravity, and yet be valueless for the purpose of refining. The New York Oil Exchange have established the following rule regarding the delivery of crude oil:

Rule IV. "Crude petroleum shall be understood to be pure natural oil, neither steamed, nor treated, free from water, sediment, or any other adulteration of the gravity of 43° to 48° Baumé."

The rule has been subsequently modified as to gravity, as very much of the natural crude oil now produced is of a lower gravity than 43°. The rest of the rule remains in force.

The test employed is one based upon actual distillation in an apparatus in all respects similar to the large stills employed in refining oils. The apparatus employed by Lockwood Bros. & Holly, petroleum importers, of Philadelphia and New York, is a small copper still modelled precisely and according to scale, after a 2500-barrel still of the cheese-box pattern. The condensing apparatus is built upon the same model. This experimental still holds