=Petroleum Products.=--The various constituents of crude petroleum differ greatly in character, some being much more volatile than others. They are separated by distillation at different temperatures. By this process naphtha, rhigoline, gasoline, benzine, and other highly inflammable products are obtained in separate receivers. By a similar process the illuminating or refined oil and the lubricating oils are also separated. The residuum consists of a gummy mass from which paraffine and petroleum jelly are extracted. _Naphtha_ usually contains several volatile compounds, including _benzine_ and _gasoline_. It is used as a solvent of grease and also of crude india-rubber, but chiefly the manufacture of illuminating gas. _Kerosene_ is the name commonly given to the refined oil. A good quality should have a fire test of not less than one hundred and fifty degrees; that is, when heated to that temperature, it should not give off any inflammable gas. This test is now mandatory in most States. _Lubricating oil_ is used almost wholly for the lubrication of heavy machinery. It varies greatly in composition and quality. _Paraffine_ or petroleum wax has largely superseded beeswax; it is used mainly in the manufacture of candles and as an insulator for electric wires. A native mineral paraffine, known as ozocerite, is mined in Utah and Galicia; it is used as an insulating material. "_Vaseline_," "_cosmoline_," or _petroleum "jelly"_ is very largely used in pharmacy as the basis of ointments and also as a lubricant for heavy machinery. _Asphalt_ is produced by the distillation of petroleum, but the greater part of the world's product comes from two "pitch lakes"--one in Bermudez, Venezuela, the other in the island of Trinidad, off the Venezuelan coast. The former is the larger and produces a superior quality. Small deposits occur near Los Angeles, Cal., and in Utah. The output of the Venezuelan asphalt is used almost wholly for street pavement. Probably no other mineral has had a wider influence on both social and economic life, and the industrial arts, than petroleum and its compounds. The kerosene lamp, the aniline dye, the insulation of electric wires, the lubrication of machinery, the cosmetic, the india-rubber solution, and the physician's sedative dose represent only a few of the devices that are derived from petroleum. =Natural Gas.=--A natural inflammable gas occurs in or near several of the petroleum horizons. One important belt extends through western Pennsylvania and New York, and another through northwestern Ohio and northeastern Indiana. It is conveyed through pipe-lines and used both as fuel and for lighting. Natural gas occurs in a great many localities, but is used commercially only in the regions noted. It is better adapted for making glass than any other fuel, and on this account extensive glass-making establishments have concentrated in the natural-gas belt of western Pennsylvania. QUESTIONS FOR DISCUSSION