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pH scale: a measure of the range of acidity and alkalinity of a substance, on a scale from 0-14, with acids being on the lower end and bases on the higher end. A value of 7 is neutral.
Perihelion: The time of the year when the Earth is closest to the Sun, (About Jan. 4).
PH Scale: A scale which measures the amount of alkalinity or acidity of different substances. The PH of pure distilled water is 7.0 ...
 See also: Atmosphere, Relative Humidity, Front, Earth, Weather
  
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