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HeadThe top of a book as it sits upright
Hot melt adhesiveAn adhesive that is liquid when hot but solid at room
temperature. Hot melt adhesives were extensively used in paperback
bindings. They are generally inflexible and can become brittle and
yellow as they age. Pages become easily detached when this happens.
HumidityThe moisture in the air. See also relative humidity
HydrolysisA chemical action involving water - decomposition in which
a compound is split into other compounds by taking up water.
HygrometerSee psychrometer
HygrothermographSee thermohygrograph
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