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Fractional Distillation

المؤلف:  GEORGE A. HOADLEY

المصدر:  ESSENTIALS OF PHYSICS

الجزء والصفحة:  P-276

2025-12-27

356

Since every liquid has its own boiling point, it is possible to separate a mixture of several that have different boiling points, by the process called fractional distillation. When crude petroleum is distilled, as soon as the boiling begins it is kept at the same temperature until no more distillate comes over. This most volatile part of the oil having been removed, the temperature is now raised a few degrees, boiling begins again, and the petroleum is kept at the new temperature as long as any vapor comes over. The process is repeated a number of times. The product that comes off last is the highest grade of all. That is it ignites at the highest temperature.

When air is liquefied and allowed to stand in a flask, the nitrogen will boil off first, since the boiling point of nitrogen is - 195°, while that of oxygen is - 183°. After the flask has stood for some time, the nitrogen will have boiled away and the liquid left will be oxygen.