Hygroscopy is the ability of a substance to attract water molecules from the surrounding environment through either absorption or adsorption. Impact of a drop of water. ... In chemistry, a molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical bonds [1] [2] [3] [4] [5]. Chemical substances are not infinitely divisible into smaller fractions of the same substance: a molecule is generally considered the smallest particle of a pure... Absorption, in chemistry, is a physical or chemical phenomenon or a process in which atoms, molecules, or ions enter some bulk phase - gas, liquid or solid material. ... Adsorption is a process that occurs when a gas or liquid or solute (called adsorbate) accumulates on the surface of a solid or more rarely a liquid (adsorbent), forming a molecular or atomic film (adsorbate). ...

Hygroscopic substances include honey, glycerin, ethanol, methanol, concentrated sulfuric acid, and concentrated sodium hydroxide (lye). Calcium chloride is so hygroscopic that it eventually dissolves in the water it absorbs: this property is called deliquescence (see below). Another example of a hygroscopic substance is biodiesel, which absorbs water to about 1200 parts per million (PPM).^{[citation needed]} Because of their affinity for atmospheric moisture, hygroscopic materials may need to be stored in sealed containers. When added to foods or other materials for the express purpose of maintaining moisture content, such substances are known as humectants. A jar of honey, shown with a wooden honey server and scones. ... Glycerin, also well known as glycerine and glycerol, and less commonly as 1,2,3-propanetriol, 1,2,3-trihydroxypropane, glyceritol, and glycyl alcohol is a colorless, odorless, hygroscopic, and sweet-tasting viscous liquid. ... Ethanol, also known as ethyl alcohol or grain alcohol, is a flammable, colorless, slightly toxic chemical compound with a distinctive perfume-like odor, and is the alcohol found in alcoholic beverages. ... Methanol, also known as methyl alcohol, wood alcohol or wood spirits, is a chemical compound with chemical formula CH3OH. It is the simplest alcohol, and is a light, volatile, colourless, flammable, poisonous liquid with a distinctive odor that is somewhat milder and sweeter than ethanol (ethyl alcohol). ... Sulfuric acid (British English: sulphuric acid), H2SO4, is a strong mineral acid. ... Sodium hydroxide (NaOH), also known as lye or caustic soda, is a caustic metallic base. ... Lye is a caustic solution used for glass and soap making. ... Calcium chloride is a chemical compound of calcium and chlorine. ... Biodiesel refers to a diesel-equivalent, processed fuel derived from biological sources (such as vegetable oils), which can be used in unmodified diesel-engined vehicles. ... Parts per million (ppm) is a measure of concentration that is used where low levels of concentration are significant. ... Atmosphere may refer to: a celestial body atmosphere, e. ... Dew on a spider web Moldy bread Moisture generally refers to the presence of water, often in trace amounts. ... Moisture content (MC) is a term used in a wide range of scientific and technical areas to express the quantity of water that a material contains. ... A humectant is a hygroscopic substance that is used as a food additive. ...

Materials and compounds exhibit different hygroscopic properties, and this difference can lead to detrimental effects, such as stress concentration in composite materials. The amount a particular material or compound is affected by ambient moisture may be considered its coefficient of hygroscopic expansion (CHE) or coefficient of hygroscopic contraction (CHC)—the difference between the two terms being a difference in sign convention and a difference in point of view as to whether the difference in moisture leads to contraction or expansion. A common example where difference in this hygroscopic property can be seen is in a paperback book cover. Often in a relatively moist environment the book cover will curl away from the rest of the book; What has happened is that the unlaminated side of the cover has absorbed more moisture than the laminated side and has increased in area, causing a stress that curls the cover toward the laminated side. This is similar to the function of a bi-metallic strip. Composite materials (or composites for short) are engineered materials made from two or more constituent materials with significantly different physical or chemical properties and which remain separate and distinct within the finished structure. ... thermocouple and Peltier_Seebeck effect. ...

The similar sounding but unrelated word hydroscopic is sometimes used in error for hygroscopic. A hydroscope is an optical device used for making observations deep under water.

History

Nitrocellulose, unlike gunpowder, is not hygroscopic. Smokeless powder facilitated the development of semi-automatic and fully automatic firearms because the hygroscopic residue of gunpowder would jam the mechanisms of such firearms. Hygroscopic types of propellants generally compensate by being readily ignitable by heat or a spark. Nitrocellulose Nitrocellulose Nitrocellulose (also: cellulose nitrate, flash paper) is a highly flammable compound formed by nitrating cellulose through, for example, exposure to nitric acid or another powerful nitrating agent. ... Smokeless powder Gunpowder, whether black powder or smokeless powder, is a substance that burns very rapidly, releasing gases that act as a propellant in firearms. ... A firearm is a kinetic energy weapon that fires either a single or multiple projectiles propelled at high velocity by the gases produced by action of the rapid confined burning of a propellant. ... A propellant is a material that is used to move an object by applying a motive force. ... Ignition occurs when the heat produced by a reaction becomes sufficient to sustain the reaction, whether it be a fire, an explosion, or nuclear fusion. ...

A common example of a hygroscopic substance is instant coffee. If left exposed to the atmosphere for a length of time (say, by spillage onto a work surface) it will deliquesce to a viscous liquid and stick to the surface. The Nordic (particularly Finnish) delicacy turkinpippuri is also hygroscopic. Instant coffee Instant coffee is a beverage derived from brewed coffee beans. ... The Nordic countries (Greenland not shown) The Nordic countries is a term used collectively for five countries in Northern Europe. ... Turkish Pepper or Tyrkisk Peber (Turkinpippuri) is a liquorice flavored zalmiak candy made by the Finnish company Fazer. ...

Building physics

Hygroscopic materials play an important role in buildings; wood is a highly hygroscopic material. Hygroscopic materials have an influence on moisture content in a room. Wood can extract moisture from air. The higher the relative humidity, the more vapour wood adsorbs. Many varieties of wood may start to rot if the relative humidity is higher than 80% for long periods. Trunks A tree trunk as found at the Veluwe, The Netherlands Wood is a solid material derived from woody plants, notably trees but also shrubs. ... Moisture content (MC) is a term used in a wide range of scientific and technical areas to express the quantity of water that a material contains. ... Boundaries: Phase, Pressure, Temperature Evaporation/Sublimation Whenever a water molecule leaves a surface, it is said to have evaporated. ... Layers of Atmosphere (NOAA) Air redirects here. ... This does not cite its references or sources. ... Adsorption is a process that occurs when a gas or liquid or solute (called adsorbate) accumulates on the surface of a solid or more rarely a liquid (adsorbent), forming a molecular or atomic film (adsorbate). ... This is a list of woods, in particular those commonly used in the timber and lumber trade. ... The aviation term ROT stands for rate one turn. ...

Biology

The seeds of some grasses have hygroscopic extensions which bend with changes in humidity, enabling them to disperse over the ground.

It's possible to split a rock by inserting a piece of wood into a fissure and adding water. As it absorbs water the wood's volume increases and pushes the sections of rock apart, increasing the fissure.

Deliquescence

Deliquescent materials are substances (mostly salts) which have a strong affinity for moisture and will absorb relatively large amount of water from the atmosphere if exposed to it, forming a liquid solution. Deliquescent salts include calcium chloride, magnesium chloride, zinc chloride, and the strong base sodium hydroxide. They are often used as desiccants. A magnified crystal of a salt (halite/sodium chloride) Salt covering the floor of Bad Water in Death Valley, CA, the lowest point in the US. A salt, in chemistry, is any ionic compound composed of cations (positively charged ions) and anions (negative ions) so that the product is neutral... Chemical affinity results from electronic properties by which dissimilar substances are capable of forming chemical compounds. ... Dew on a spider web Moldy bread Moisture generally refers to the presence of water, often in trace amounts. ... Impact of a drop of water. ... Layers of Atmosphere (NOAA) Air redirects here. ... A liquid will usually assume the shape of its container. ... Dissolving table salt in water This article is about a chemical solution; for other uses of the term solution, see solution (disambiguation). ... A magnified crystal of a salt (halite/sodium chloride) Salt covering the floor of Bad Water in Death Valley, CA, the lowest point in the US. A salt, in chemistry, is any ionic compound composed of cations (positively charged ions) and anions (negative ions) so that the product is neutral... Calcium chloride is a chemical compound of calcium and chlorine. ... Magnesium chloride is composed of magnesium and chlorine and is a typical ionic halide, being highly polar and soluble in water. ... Zinc chloride (ZnCl2) is a colorless or white compound of zinc and chlorine that is extremely hygroscopic. ... Sodium hydroxide (NaOH), also known as lye or caustic soda, is a caustic metallic base. ... A desiccant is a substance that adsorbs moisture from the air. ...

See also

• Hydrophobic and Hydrophilic