Coagulation - Gyoketsu (English spelling)

Japanese: 凝結 - ぎょうけつ（英語表記）coagulation

This refers to the process in which colloidal particles dispersed in a liquid or gas gather together to form larger particles and precipitate. It is used synonymously with coagulation, coagulation, and condensation, and is often used synonymously with condensation. It is also called coagulation.

When an electrolyte is added to a sol, ions of the opposite sign are adsorbed onto the colloidal particles, neutralizing the charge of the particles and causing coagulation. The higher the valence of the ions, the greater the coagulation effect. The amount of electrolyte required to coagulate a colloid within a certain amount of time is called the coagulation value or precipitation value.

Sol coagulation can also be seen when a sol is frozen or when two types of sol are mixed. Also, substances such as proteins coagulate when heated (called thermal coagulation). When two types of hydrophobic colloids with opposite charges, such as arsenic sulfide sol and iron hydroxide sol, are mixed together, they coagulate with each other. However, there is also a method of adding a hydrophilic colloid to a hydrophobic colloid to obtain a stable colloid. This is called a protective colloid.

[Toshihisa Yoshida]

weather

As an atmospheric phenomenon, water vapor in the atmosphere turns into water, condensing on the surfaces of features as dew, and in space as fog or clouds. The amount of water vapor contained in the air is usually expressed as water vapor pressure. The upper limit that it can contain is determined by temperature and is expressed as saturation vapor pressure. The lower the temperature, the lower the saturated water vapor pressure. Therefore, if the temperature of an air parcel containing a certain amount of water vapor drops, the water vapor pressure will eventually reach the saturation value, and if the temperature drops further, the amount of water vapor that cannot be contained will turn into liquid. This is dew, fog, and clouds.

The most important phenomenon that lowers the temperature of an air mass is the ascent of that air mass. When an air current hits a mountain, it rises. Also, when a cold air mass collides with a warm air mass, the warm air mass rises above the cold air mass. Since the atmospheric pressure is lower the higher up the air mass, the rising air mass expands and its temperature drops. The altitude at which water vapor reaches its saturation value during the ascent is called the condensation height. Therefore, the condensation height corresponds to the height of the cloud base. This is the reason why clouds appear on mountain tops and on fronts associated with low pressure. The less water vapor contained in an air mass, the higher the condensation height.

[Hiroo Misaki]

"The Physics of Clouds - From Cloud Droplet Formation to Cloud Movement" by Takahashi Takashi (1987, Tokyodo Publishing) " ▽ "The Science of Water Cycle - The Behavior of Cloud Clusters" by Takeda Takao (1987, Tokyodo Publishing)" ▽ "The Latest Colloid Chemistry" by Kitahara Fumio and Furusawa Kunio (1990, Kodansha)" ▽ "The Fundamentals of Interface and Colloid Chemistry" by Kitahara Fumio (1994, Kodansha)" ▽ "The Chemistry of Dispersion and Coagulation" by Moriyama Noboru (1995, Sangyo Tosho)" ▽ "Heavy Rain and Precipitation Systems" by Ninomiya Kozo (2001, Tokyodo Publishing)"

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

液体または気体中に分散しているコロイドのような微粒子が集合して、より大きい粒子をつくり沈殿することをいう。凝集、凝固、凝縮などと同義に使われ、とくに凝縮と同義に用いることが多い。凝析ともいう。

　ゾルに電解質を加えると、コロイド粒子に反対符号のイオンが吸着して、粒子の電荷が中和されるため凝結がおこる。このときイオンの価数が大きいほど凝結の効果は大きい。一定時間内でコロイドを凝結させるのに必要な電解質の量を凝結価あるいは沈殿価という。

　ゾルの凝結は、ゾルを凍らせた場合とか、2種のゾルを混合した場合などでもみられる。また、タンパク質のようなものは熱すると凝結（熱凝結という）する。硫化ヒ素ゾルと水酸化鉄ゾルのように反対の電荷をもつ2種の疎水コロイドを混ぜると互いに凝結をおこす。しかし疎水コロイドに親水コロイドを加えて安定なコロイドを得る方法もある。これを保護コロイドという。

［吉田俊久］

気象

大気現象としては、大気中の水蒸気が水に変わることで、地物の表面で凝結して露となり、空間で凝結して霧や雲となる。空気中に含まれる水蒸気量は普通、水蒸気圧で表される。その含みうる上限は温度によって定まり、飽和水蒸気圧で表される。温度が低いほど飽和水蒸気圧は低い。したがって一定の水蒸気量を含む空気塊の温度が下がれば、水蒸気圧はいずれは飽和値に達し、温度がさらに下がれば、含みきれなくなった分だけ水蒸気が液相に変わる。これが露、霧、雲である。

　空気塊の温度を下げることになるもっとも重要な現象は、その空気塊の上昇である。気流が山岳に当たれば上昇する。また冷気塊と暖気塊とが衝突すれば、暖気塊は冷気塊の上にはい上がる。大気は上空ほど気圧が低いので、上昇気塊は膨張しそのために温度が下がる。上昇途中で水蒸気が飽和値に達する高度を凝結高度という。したがって凝結高度は雲底の高さに相当する。山頂部に雲がかかったり、低気圧に伴う前線上に雲を生ずるのはこの理由による。気塊中に含まれている水蒸気量が少ないほど、凝結高度は高い。

［三崎方郎］

『高橋劭著『雲の物理――雲粒形成から雲運動まで』（1987・東京堂出版）』▽『武田喬男著『水循環の科学――雲の群れのふるまい』（1987・東京堂出版）』▽『北原文雄・古沢邦夫著『最新コロイド化学』（1990・講談社）』▽『北原文雄著『界面・コロイド化学の基礎』（1994・講談社）』▽『森山登著『分散・凝集の化学』（1995・産業図書）』▽『二宮洸三著『豪雨と降水システム』（2001・東京堂出版）』