| Section C | C index | 671-679 of 1157 terms |
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colloidal system—(Also called colloidal dispersion, colloidal suspension.) An intimate mixture of two substances, one of which, called the dispersed phase (or colloid), is uniformly distributed in a finely divided state through the second substance, called the dispersion medium (or dispersing medium). The dispersion medium may be a gas, a liquid, or a solid and the dispersed phase may also be any of these, with the exception of one gas in another. A system of liquid or solid particles colloidally dispersed in a gas is called an aerosol. A system of solid substance or water-insoluble liquid colloidally dispersed in liquid water is called a hydrosol. There is no sharp line of demarcation between true solutions and colloidal systems or between mere suspensions and colloidal systems. When the particles of the dispersed phase are smaller than about 10−3 μm in diameter, the system begins to assume the properties of a true solution; when the particles dispersed are much greater than 1 μm, separation of the dispersed phase from the dispersing medium becomes so rapid that the system is best regarded as a suspension. According to the latter criterion, natural clouds in the atmosphere should not be termed aerosols; however, since many cloud forms apparently exhibit characteristics of true colloidal suspensions, this strict physico-chemical definition is often disregarded for purposes of convenient and helpful analogy. Condensation nuclei and many artificial smokes may be regarded as aerosols.
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color look-up table—(Abbreviated CLUT.) A mapping of a pixel value to a color value shown on a display device. Typically, a CLUT will map the input into a color presentation, but if all colors are of equal intensity for each input value, then a gray scale or black-and-white image results.
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Colorado low—In the United States, a low that makes its first appearance as a definite center in the vicinity of Colorado on the eastern slopes of the Rocky Mountains. It is, in most aspects, analogous to the Alberta low.
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Colorado sunken pan—A type of evaporation pan that is about 1 m (3 ft) square and 0.5 m (18 in.) deep. This pan is sunk into the ground to within about 5 cm (2 in.) of its rim, and the water is maintained at about ground level. It is made of unpainted galvanized iron. The pan coefficient, on an annual basis, is about 0.8.
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colored rain—Rain that leaves a colored stain on the ground and on exposed objects, often red or rusty in hue. The coloration is usually the result of rain picking up particles as it falls through a dust-filled subcloud layer. The subcloud layer, usually rich in iron oxide, may originate from an area far from the observed colored rain event. This phenomenon has been observed frequently in Italy with particles advected northward from the Sahara. See blood rain.
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colorimetry—Form of absorption spectroscopy in which a reagent that bonds with the species of interest is added to a liquid solution, resulting in a change in color of the solution. The method has been applied, for example, in the determination of the content of certain metals in atmospheric aerosols.
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column abundance—The amount of an atmospheric trace gas found in a vertical column of the atmosphere, usually expressed in units of molecules per unit area. Most often used in reference to ozone. See Dobson unit.
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column model—A numerical model in which solutions depend only on the vertical coordinate and time. These models are most useful near boundaries where vertical gradients dominate flow evolution. See mixed-layer models.
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