Hygroscopic
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A hygroscopic or hydroscopic substance is a substance that adsorbs water readily from its surroundings.
An example is biodiesel, which absorbs water to about 1200 parts per million (PPM). Other hygroscopic substances include ethyl alcohol, methanol, glycerin, concentrated sulfuric acid and concentrated sodium hydroxide.
Those using hygroscopic materials should be advised to keep them in sealed containers, as they will absorb water from the air.
History
Nitrocellulose, unlike gunpowder, is not hygroscopic. Smokeless powder facilitated the development of semi-automatic and fully automatic firearms. This is because the hygroscopic residue of gunpowder would jam the mechanisms of such firearms. Hygroscopic components of bullets generally compensate by being readily ignitable by heat or a spark.
Building Physics
Hygroscopic materials play an important role in buildings. For example wood is a highly hygroscopic material. Hygroscopic materials have an influence on moisture content in a room. Wood can extract moisture (vapour) from air. The higher the relative humidity, the more vapour wood adsorbs. If the relative humidity is higher than 80% wood starts to rot.