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.