The testing of kerosene oils is by far the most important of all, because the conditions under which it is used in ordinary lamps are especially favorable for the occurrence of explosions. Kero sene is tested for acid, sulphur, gravity, color, and what is known as the "fire test." Acid and grav ity tests are the same as for naphthas. Color is, of course, determined by inspection, and furnishes the basis for division of the kerosene into the three grades common in this country : water white, which is colorless, and is the standard of American kero sene; prime white, of a faint yellow color; and standard or standard white, a pronounced yellow. In European countries other grades are recog nized, as many as seven being commonly sold in Germany.
The fire tests, however, are the most significant since they determine the safe or unsafe character of the kerosene and the legality of its sale. Two fire tests may be used, one of them called the "flash test," determining the temperature at which the oil will give off an inflammable vapor when heated artificially, or when exposed naturally to the air. The other; known as the "burning test," deter mines the temperature at which the oil will take fire and burn on the surface. The latter tempera ture is usually from ten to forty degrees higher than the "flashing point," and, since the gravest dangers are from the generation of explosive va pors, the flash test means most.
A great number of devices have been invented for making the flash test, the essential principle of each being a closed or open cup in which the oil is heated. A common form of tester consists of a cup holding about the same amount of oil as a me dium-sized lamp, the cup being immersed in water and heated carefully by heating the water, on the same principle as cooking in a double boiler. The glass cover of the cup has a hole for a thermome ter and another for inserting a match to ignite the vapor. Kerosene, to be safe for lighting purposes, should have a flashing point higher than any tem perature which it is likely to reach under ordinary conditions. In most places a flashing point of 110° or higher is required by law. Testing, how ever, usually begins as soon as the thermometer shows the oil to have a temperature of about 85° or 90°, and continues at intervals of every degree or two until the insertion of the match causes the appearance of a bluish flame in the cup. As soon as this "flash" flame appears the reading of the thermometer indicates whether the oil is up to the required standard. Illuminating oils for special purposes, such as headlight oil for locomotives, sig nal lamps, miners lamps, and so on, frequently have to meet much higher requirements than for or dinary domestic use, but the testing process is the same.
Lubricating oils are subjected to three impor tant tests, viscosity, fire test, and cold test, each, in a way, being of vital significance in determining the value of the oil. The first, if any, is perhaps the most important since viscosity is the most nec essary quality of any lubricating fluid. The test may be made in innumerable ways, but all depend on the principle of determining the length of time required for a given quantity of the oil to flow through a small opening. The temperature at which the test is made depends on the special use for which the individual oil is intended, ranging up as high as 212° in the case of cylinder oils for steam engines.
The fire test is necessary in the case of most ma chine and engine oils because the heat from fric tion might generate inflammable vapors if very volatile products were present. The cold test is also required to determine the temperature at which the oil would become thick and cloudy. This test is made by freezing the oil in a tube, and then as it melts, noting the temperature at which it be gins to run. High-grade lubricating oils have to withstand a very wide range of temperatures ; firstt quality cylinder oil, for example, must have a cold test as low as 55°, and it must not flash below 550° Fahrenheit.
All these tests must be made at the refinery for each lot of distillates before they can be approved, graded, and loaded for shipment to the consumer. If any distillate does not "prove up," it has to go back for further manipulation to remedy the de fects, the success or failure of the tests depending largely on the skill of the stillman in making his cuts as the distillate passes through his separating box.
In spite of its many steps and intricate processes there is nothing picturesque or spectacular in pe troleum refining, unless it is in the magnitude of the plant and the very obscurity of the many trans formations going on everywhere yet entirely un seen. One refinery is essentially the same as every other save in size, and perhaps in a few minor de tails. At a hundred refineries from the Atlantic to the Pacific, and from the Lakes to the Gulf, the same story is repeated day after day and year after year, as the invisible stream of oil makes its jour ney step by step through the maze of pipes, stills, condensers, and agitators, leaving at every turn a part of its precious burden. On the one hand, the vast network of pipe lines binds the refinery to thousands of wells, scattered halfway across the continent. On the other hand, the world-wide dis tributing system carries the multitude of refined products into the daily life of every class of hu manity.