This section is from "Scientific American Supplement Volumes 275, 286, 288, 299, 303, 312, 315, 324, 344 and 358". Also available from Amazon: Scientific American Reference Book.
Nothing is in more general use than petroleum, and but few things are known less about by the majority of persons. It is hydra-headed. It appears in many forms and under many names. "Burning fluid" is a popular name with many unscrupulous dealers in the cheap and nasty. "Burning fluid" is usually another name for naphtha, or something worse. Gasoline, naphtha, benzine, kerosene, paraffine, and many other dangerous fluids which make the fireman's vocation necessary are all the product of petroleum. These oils are produced by the distillation or refining of crude petroleum, and inasmuch as the public, especially firemen, are daily brought into contact with them it is proper that they should know something of their properties. Refining as commonly practiced involves three successive operations. The apparatus employed consists of an iron still connected with a coil or worm of wrought-iron pipe, which is submerged in a tank of water for the purpose of cooling it. The end of this pipe is fixed with a movable spout, which can be transferred or switched from one to another of half a dozen pipes which come around close to it, but which lead into different tanks containing different grades of the distillate. When the still has been filled with crude oil the fire is lighted beneath it, and soon the oil begins to boil. The first products of distillation are gases which, at ordinary temperatures, pass through the coil without being condensed, and escape. When the vapors begin to condense in the worm the oil trickles from the end of the coil into the pipe leading to the appropriate receiving tank.
The first oil obtained is known as gasoline, used in portable gas machines for making illuminating gas. Then, in turn, come naphthas of a greater or less gravity, benzine, high test water white burning oil, such as Pratt's Astral common burning oil or kerosene, and paraffine oils. When the oil has been distilled it is by no means fit for use, having a dirty color and most offensive smell; it is then refined. For this purpose it is pumped into a large vat or agitator, which holds from two hundred and fifty to one thousand barrels. There is then added to the oil about two per cent, of its volume of the strongest sulphuric acid. The whole mixture is then agitated by means of air pumps, which bring as much as possible every particle of oil in contact with the acid. The acid has no affinity for the oil, but it has for the tarry substance in it which discolors it, and, after the agitation, the acid with the tar settles to the bottom of the agitator, and the mixture is drawn off into a lead-lined tank. After the removal of the acid and tar, the clear oil is agitated with either caustic soda or ammonia and water. The alkali neutralizes the acid remaining in the oil, and the water removes the alkali, when the process of refining is finished. A few refiners improve the quality of their refined oil by redistilling it after treating it with acid and alkali. All distillates of petroleum have to be treated with acid and alkali to refine them. There is one thing peculiar about the distillates of petroleum, and that is that the run which follows naphtha, which is called "the middle run oil," is the highest test oil that is made, running as high as 150 and 160 degrees flash, while the common oil which follows, viz., from 45 down to 33 degrees Baume, will range at only about 100 flash, or 115 and 120 degrees burning lest.
An oil that will stand 100 flash will stand 110 burning test every time. Kerosene oil, at ordinary temperature, should extinguish a match as readily as water. When heated it should not evolve an inflammable vapor below 110 degrees, or, better, 120 degrees Fahrenheit, and should not take fire below 125 to 140 degrees Fahrenheit. As the temperature in a burning lamp rarely exceeds 100 degrees Fahrenheit, such an oil would be safe. It would produce no vapors to mix with the air in the lamp and make an explosive mixture; and, if the lamp should be overturned, or broken, the oil would not be liable to take fire. The crude naphtha sells at from three to five cents per gallon, while the refined petroleum or kerosene sells at from fifteen to twenty cents. As great competition exists among the refiners, there is a strong inducement to turn the heavier portions of the naphtha into the kerosene tank, so as to get for it the price of kerosene. In this way the inflammable naphtha or benzine is sometimes mixed with the kerosene, rendering the whole highly dangerous. Dr. D. B. White, President of the Board of Health of New Orleans, found that experimenting on oil which flashed at 113 degrees Fahrenheit, an addition of one per cent. of naphtha caused it to flash at 103 degrees; two per cent. brought the flashing point down to 92 degrees, five per cent. to 83 degrees, ten per cent. to 59 degrees, and twenty per cent. of naphtha added brought the flashing point down to 40 degrees Fahrenheit. After the addition of twenty per cent. of naphtha the oil burned at 50 degrees Fahrenheit. There are two distinct tests for oil, the flashing test and the burning test. The flashing test determines the flashing point of the oil, or the lowest temperature at which it gives off an inflammable vapor. This is the most important test, as it is the inflammable vapor, evolved at atmospheric temperatures, that causes most accidents. Moreover, an oil which has a high flashing test is sure to have a high burning test, while the reverse is not true. The burning test fixes the burning point of the oil, or the lowest temperature at which it takes fire. The burning point of an oil is from ten to fifty degrees Fahrenheit higher than the flashing point. The two points are quite independent of each other; the flashing point depends upon the amount of the most volatile constituents present, such as naphtha, etc., while the burning point depends upon the general character of the whole oil. One per cent. of naphtha will lower the flashing point of an oil ten degrees without materially affecting the burning test. The burning test does not determine the real safety of the oil, that is, the absence of naphtha. The flashing test should, therefore, be the only test, and the higher the flashing point the safer the oil.