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In chemistry, Henry's law is one of the gas laws formulated by the English chemist William Henry, who studied the topic in the early 19th century. In his publication about the quantity of gases absorbed by water, he described the results of his experiments: :''..."water takes up, of gas condensed by one, two, or more additional atmospheres, a quantity which, ordinarily compressed, would be equal to twice, thrice, &c. the volume absorbed under the common pressure of the atmosphere."'' In other words, the amount of dissolved gas is proportional to its partial pressure in the gas phase. The proportionality factor is called the Henry's law constant. An everyday example of Henry's law is given by a carbonated soft drink in a bottle. Before it is opened, the gas above the drink is almost pure carbon dioxide at a pressure higher than atmospheric pressure. The drink itself contains dissolved carbon dioxide. When the bottle is opened, this gas escapes, giving the characteristic hiss. Because the partial pressure of carbon dioxide above the liquid is now much lower, some of the dissolved carbon dioxide comes out of the solution as bubbles. If the drink is left in the open, the concentration of carbon dioxide in solution will come into equilibrium with the carbon dioxide in the air, and the drink will go "flat". Another example is the depth-dependent dissolution of oxygen and nitrogen in the blood of underwater divers (decompression and decompression sickness). == Fundamental types and variants of Henry's law constants == There are many ways to define the proportionality constant of Henry's law, which can be subdivided into two fundamental types: One possibility is to put the aqueous phase into the numerator and the gas phase into the denominator ("aq/gas"). This results in the Henry's law solubility constant . Its value increases with increased solubility. Alternatively, numerator and denominator can be switched ("gas/aq"), which results in the Henry's law volatility constant . The value of decreases with increased solubility. There are several variants of both fundamental types. This results from the multiplicity of quantities that can be chosen to describe the composition of the two phases. Typical choices for the aqueous phase are molar concentration (), molality (), and molar mixing ratio (). For the gas phase, molar concentration () and partial pressure () are often used. It is not possible to use the gas-phase mixing ratio () because at a given gas-phase mixing ratio, the aqueous-phase concentration depends on the total pressure and thus the ratio is not a constant. To specify the exact variant of the Henry's law constant, two superscripts are used. They refer to the numerator and the denominator of the definition. For example, refers to the Henry solubility defined as . 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Henry's law」の詳細全文を読む スポンサード リンク
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