1.Chemistry. a. A suspension of finely divided particles in a continuous medium in which the particles are approximately 5 to 5,000 angstroms in size, do not settle out of the substance rapidly, and are not readily filtered. b. The particulate matter so suspended.
2.Physiology. The gelatinous product of the thyroid gland, consisting mainly of thyroglobulin, which serves as the precursor and storage form of thyroid hormone.
3.Pathology. Gelatinous material resulting from colloid degeneration in diseased tissue.
Of, relating to, containing, or having the nature of a colloid.
- colloi´dal (ke-loid´l, kò-) adjective
- colloi´dally adverb
Colloid, mixture of tiny particles of one substance, called the dispersed phase, suspended in another substance, called the dispersion medium. The particles are so small that they remain in suspension indefinitely, unaffected by gravity. Both the dispersed phase and the dispersion medium may be solid, liquid, or gaseous, although the dispersal of one gas in another is not known as colloidal dispersion.
An aerosol is a colloidal dispersion of either a solid or a liquid in a gas. An emulsion is a colloidal dispersion of a liquid in another liquid. A sol is a colloidal dispersion of solid particles in a liquid. A gel is a sol in which the suspended particles are organized in a loose but definite three-dimensional arrangement, giving some rigidity and elasticity to the mixture.
Because of their small size, colloidal particles can pass through ordinary filters, but not through the extremely fine openings in a semipermeable membrane, such as parchment. Although individual colloidal particles are too small to be seen with an ordinary microscope, they can be made visible by means of an ultramicroscope, or dark-field microscope. The particles are directly visible in an electron microscope.
1.Symbol Ag. A lustrous white, ductile, malleable metallic element, occurring both uncombined and in ores such as argentite, having the highest thermal and electrical conductivity of the metals. It is highly valued for jewelry, tableware, and other ornamental use and is widely used in coinage, photography, dental and soldering alloys, electrical contacts, and printed circuits. Atomic number 47; atomic weight 107.868; melting point 960.8°C; boiling point 2,212°C; specific gravity 10.50; valence 1, 2.
2.This metallic element as a commodity or medium of exchange.
3.Coins made of this metallic element.
4.a. Domestic articles, such as tableware, made of or plated with silver. b. Tableware, especially eating and serving utensils, made of steel or another metal.
5.Color. A lustrous medium gray.
6.A silver salt, especially silver nitrate, used to sensitize paper.
1.Made of or containing silver: a silver bowl; silver ore.
2.Resembling silver, especially in having a lustrous shine; silvery.
3.Color. Of a lustrous medium gray: silver hair.
4.Having a soft, clear, resonant sound.
5.Eloquent; persuasive: a silver voice.
6.Favoring the adoption of silver as a standard of currency: the silver plank of the 1896 Democratic platform.
7.Of or constituting a 25th anniversary.
silvered, silvering, silvers verb, transitive
1.To cover, plate, or adorn with silver or a similar lustrous substance.
2.To give a silver color to.
3.To coat (photographic paper) with a film of silver nitrate or other silver salt.
To become silvery.
[Middle English, from Old English siolfor, seolfor, probably ultimately from Akkadian sarpu, refined silver, from sarâpu, to smelt, refine.]
Silver, symbol Ag, white, shiny metallic element that conducts heat and electricity better than any other metal. Silver is one of the transition elements of the periodic table. The atomic number of silver is 47, and the atomic weight is 107.868.
Properties and Occurrence
With the exception of gold, silver is the most malleable and ductile of all metals. Chemically it is not very active. Sulfur and sulfides attack silver, causing tarnishing, which is the formation of silver sulfide on the metal's surface.
Silver sometimes occurs in a pure form, with the most notable deposits in Peru and Norway. Pure silver is also found with pure gold in an alloy called electrum, and considerable amounts of silver are recovered in the processing of gold. Silver is usually found combined with other elements in minerals and ores. Important silver minerals include cerargyrite (horn silver), pyrargyrite, and argentite. Silver also occurs as a constituent of lead, copper, and zinc ores, and half the world production of silver is a by-product in the processing of such ores. Practically all the silver produced in Europe is obtained from the lead sulfide ore, galena.
The use of silver in jewelry, tableware, and coinage is well known. It is usually alloyed with small amounts of other metals to make it harder and more durable. Sterling silver for tableware and other solid-silver objects is 92.5 percent silver and 7.5 percent copper. Silver is used to coat smooth glass surfaces for mirrors, although aluminum has largely replaced silver in this application. Silver is also widely used in electrical and electronic components. Colloidal silver, dilute solutions of silver nitrate, and some insoluble compounds, such as potassium, are used in medicine as antiseptics and bactericides. Silver bromide, silver chloride, and silver iodide all darken when exposed to light and are therefore used in coatings for photographic plates, film, and paper.