viscose process, method widely used for the commercial preparation of rayon. Cellulose, prepared from either wood pulp or, less commonly, cotton linters, is treated with sodium hydroxide (an alkali) and then with carbon disulfide, the resulting product being a substance called cellulose xanthate. Dissolved in sodium hydroxide, this alkaline cellulose xanthate forms a thick solution called viscose. Rayon yarn is made by forcing the viscose through tiny openings in a spinneret into an acid solution, which coagulates it in the form of fine strands. Most of the rayon manufactured today is produced by this method, al though other processes are also in use. The viscose process was discovered in 1892 by the English chemist Charles Frederick Cross and his collaborator, Edward John Bevan.

process, in law: see procedure.

open-hearth process: see steel.

lead chamber process: see sulfuric acid.

froth-flotation process: see flotation process.

four-color process: see printing.

flotation process, in mineral treatment and mining, process for concentrating the metal-bearing mineral in an ore. Crude ore is ground to a fine powder and mixed with water, frothing reagents, and collecting reagents. When air is blown through the mixture, mineral particles cling to the bubbles, which rise to form a froth on the surface. The waste material (gangue) settles to the bottom. The froth is skimmed off, and the water and chemicals are distilled or otherwise removed, leaving a clean concentrate. The process, also called the froth-flotation process, is used for a number of minerals, especially silver.

due process of law: see Fourteenth Amendment.

cyanide process or cyanidation, method for extracting gold from its ore. The ore is first finely ground and may be concentrated by flotation; if it contains certain impurities, it may be roasted. It is then mixed with a dilute solution of sodium cyanide (or potassium or calcium cyanide) while air is bubbled through it. The gold is oxidized and forms the soluble aurocyanide complex ion, Au(CN)₂^-1. (Silver, usually present as an impurity, forms a similar soluble ion.) The solution is separated from the ore by methods such as filtration, and the gold is precipitated by adding powdered zinc. The precipitate usually contains silver, which is also precipitated, and unreacted zinc. The precipitate is further refined, e.g., by smelting to remove the zinc and by treating with nitric acid to dissolve the silver. The cyanide process was developed (1887) by J. S. MacArthur and others in Glasgow, Scotland. It is now the most important and widely used process for extracting gold from ores.

cyanamide process: see ammonia.

contact process: see sulfuric acid.

basic oxygen process, method of producing steel from a charge consisting mostly of pig iron. The charge is placed in a furnace similar to the one used in the Bessemer process of steelmaking except that pure oxygen instead of air is blown into the charge to oxidize the impurities present. One desirable feature of this process is that it takes less than an hour, and is thus much faster than the open-hearth process, another important method of steelmaking. A second advantage is that a major byproduct is carbon monoxide, which can be used as a fuel or in producing various chemicals, such as acetic acid. The basic oxygen process also produces less air pollution than methods using air.

amalgamation process, in particular, a method to extract gold and silver from ores. The ore is crushed and treated with mercury, in which the metal dissolves. The amalgam is heated and the mercury evaporates, leaving pure gold or silver. The process has been criticized as an environmental and occupational threat due to the extreme toxicity of mercury.

Wacker process, an industrial process for the manufacture of ethanol by oxidizing ethene. For example, bubbling ethylene and oxygen when treated by an acidified water solution of palladium and cupric chlorides yield acetaldehyde; reaction is catalyzed by PdCl₂-CuCl₂. During the reaction palladium forms a complex with ethylene, is reduced to Pd(0), and is then reoxidized by Cu(II). The process is run in one vessel at 50-130^oC and at pressures of 3-10 atm. Regeneration of cupric chloride occurs in a separate oxidizer. The favorable economics of the process is due to the abundance of ethylene. Oxidation of propylene to acetone is accomplished at 110-120^oC with 10-14 atm.

Solvay process [for Ernest Solvay], commercial process for the manufacture of sodium carbonate (washing soda). Ammonia and carbon dioxide are passed into a saturated sodium chloride solution to form soluble ammonium hydrogen carbonate, which reacts with the sodium chloride to form soluble ammonium chloride and a precipitate of sodium hydrogen carbonate (sodium bicarbonate) if the temperature is maintained below 15°C;. The sodium hydrogen carbonate is filtered off and heated to produce sodium carbonate.

Parkes process: see silver.

Mond process: see under Mond, Ludwig.

Haber process, commercial process for the synthesis of ammonia, NH₃. Pure hydrogen and nitrogen gases are mixed in the appropriate proportion, heated to between 450°C; and 600°C;, compressed to about 1,000 atmospheres pressure, and passed over a catalyst. The reaction is 3H₂+N₂⇌ 2NH₃+heat. The ammonia gas is liquefied by rapid cooling; unreacted nitrogen and hydrogen are returned to the reaction chamber. This process, developed by Fritz Haber in 1909, was the first commercially important high-pressure chemical process.

Frasch process [for Herman Frasch, the German-American chemist who devised it], process for the extraction of sulfur from subsurface deposits. Three pipes, one inside another, are sunk to the bottom of the sulfur bed. Water heated under pressure to a temperature well above the melting point of the sulfur is conducted down the outer pipe, and air under pressure down through the innermost pipe. The heated water melts the sulfur and the compressed air forces it through the middle pipe to the surface.

Fischer-Tropsch process, method for the synthesis of hydrocarbons and other aliphatic compounds. Synthesis gas, a mixture of hydrogen and carbon monoxide, is reacted in the presence of an iron or cobalt catalyst; much heat is evolved, and such products as methane, synthetic gasoline and waxes, and alcohols are made, with water or carbon dioxide produced as a byproduct. An important source of the hydrogen-carbon monoxide gas mixture is the gasification of coal (see water gas). The process is named after F. Fischer and H. Tropsch, the German coal researchers who discovered it in 1923.

Bessemer process [for Sir Henry Bessemer], industrial process for the manufacture of steel from molten pig iron. The principle involved is that of oxidation of the impurities in the iron by the oxygen of air that is blown through the molten iron; the heat of oxidation raises the temperature of the mass and keeps it molten during operation. The process is carried on in a large container called the Bessemer converter, which is made of steel and has a lining of silica and clay or of dolomite. The capacity is from 8 to 30 tons of molten iron; the usual charge is 15 or 18 tons. The converter is egg-shaped. At its narrow upper end it has an opening through which the iron to be treated is introduced and the finished product is poured out. The wide end, or bottom, has a number of perforations (tuyères) through which the air is forced upward into the converter during operation. The container is set on pivots (trunnions) so that it can be tilted at an angle to receive the charge, turned upright during the "blow," and inclined for pouring the molten steel after the operation is complete. As the air passes upward through the molten pig iron, impurities such as silicon, manganese, and carbon unite with the oxygen in the air to form oxides; the carbon monoxide burns off with a blue flame and the other impurities form slag. Dolomite is used as the converter lining when the phosphorus content is high; the process is then called basic Bessemer. The silica and clay lining is used in the acid Bessemer, in which phosphorus is not removed. In order to provide the elements necessary to give the steel the desired properties, another substance (often spiegeleisen, an iron-carbon-manganese alloy) is usually added to the molten metal after the oxidation is completed. The converter is then emptied into ladles from which the steel is poured into molds; the slag is left behind. The whole process is completed in 15 to 20 min. The Bessemer process was superseded by the open-hearth process (see steel). See also metallurgy.

Ben Day, or Benday, process: see printing.

Bayer process, procedure for obtaining alumina from the aluminum ore bauxite. The alumina can then be used for various industrial purposes or smelted to provide aluminum. The first step in the process is the mixing of ground bauxite into a solution of sodium hydroxide. By applying steam and pressure in tanks containing the mixture, the bauxite slowly dissolves. The alumina released reacts with the sodium hydroxide to form sodium aluminate. After the contents of the tank have passed through other vessels where the pressure and temperature are reduced and impurities are removed, the solution of sodium aluminate is placed in a special tank where the alumina is precipitated out. The precipitate is removed from the tank, washed, and heated in a kiln to drive off any water present. The residue is a commercially pure alumina.

or thought

Action of using one's mind to produce thoughts, or covert symbolic responses to stimuli. Theories of thought and thought processes have concentrated largely on directed thinking, including problem solving. At the beginning of the 20th century, researchers focused on studying mental associations. Theorists of Gestalt psychology in the 1920s and '30s believed the elements of thought to be in the nature of patterns elicited from experience. Today these elements are often regarded as bits of information undergoing processing. Seealso cognitive psychology, information processing.

Learn more about thinking with a free trial on Britannica.com.

In probability theory, a family of random variables indexed to some other set and having the property that for each finite subset of the index set, the collection of random variables indexed to it has a joint probability distribution. It is one of the most widely studied subjects in probability. Examples include Markov processes (in which the present value of the variable depends only upon the immediate past and not upon the whole sequence of past events), such as stock-market fluctuations, and time series (in which temperature or rainfall measurements, for example, are taken at the same time each day over several days).

Learn more about stochastic process with a free trial on Britannica.com.

20th-century school of philosophy that emphasizes the elements of becoming, change, and novelty in experienced reality and opposes the traditional Western philosophical stress on being, permanence, and uniformity. Reality, including both the natural world and the human sphere, is essentially historical in this view, emerging from (and bearing) a past and advancing into a novel future. Hence, it cannot be grasped by old static spatial concepts that ignore the temporal and novel aspects of the universe given in human experience. The foremost contributors to process philosophy have been Henri Bergson and Alfred North Whitehead.

Learn more about process philosophy with a free trial on Britannica.com.

or Mexican process

Method of isolating silver from its ore, apparently dating from pre-Columbian times. The ore was crushed and ground by mule power in arrastras, reducing it to a fine mud. This was then spread over a courtyard or patio, sprinkled with mercury, salt, and copper sulfate, and mixed by driving mules over it. Chemical reactions caused the silver to dissolve in the mercury. When the amalgamation was complete, the material was agitated with water in large tubs and the mud run off. The amalgam at the bottom was collected and heated to drive off the mercury. Used for much of the world's silver production for 350 years, the process was replaced by the cyanide process early in the 20th century.

Learn more about patio process with a free trial on Britannica.com.

or Siemens-Martin process

Steelmaking technique that for most of the 20th century accounted for most steel made in the world. William Siemens made steel from pig iron in a reverberatory furnace of his design in 1867. The same year the French manufacturer Pierre-Émile Martin (1824–1915) used the idea to produce steel by melting wrought iron with steel scrap. Siemens used the waste heat given off by the furnace: he directed the fumes from the furnace through a brick checkerwork, heating it to a high temperature, and then used the same path to introduce air into the furnace; the preheated air significantly increased the flame temperature. The open-hearth process furnace (which replaced the Bessemer process) has itself been replaced in most industrialized countries by the basic oxygen process and the electric furnace. Seealso reverberatory furnace.

Learn more about open-hearth process with a free trial on Britannica.com.

Traditional method of producing molds for metal sculpture and other castings. It requires a positive, a core made of refractory material and an outer layer of wax. The positive can be produced either by direct modeling in wax over a prepared core (direct lost-wax casting), or by casting in a piece mold or flexible mold taken from a master cast. The wax positive is invested with a mold made of refractory materials and heated to melt the wax, leaving a narrow cavity between the core and the investment. Molten metal is poured into this cavity. When the metal has solidified, the investment and core are broken away. Seealso investment casting.

Learn more about lost-wax casting with a free trial on Britannica.com.

Chemical method for producing wood pulp using caustic soda and sodium sulfide as the liquor in which the pulpwood is cooked to loosen the fibres. The process (from German kraft, “strong”) produces particularly strong and durable paper; another advantage is its capability of digesting pine chips; resins dissolve in the alkaline liquor and are recovered as tall oil, a valuable by-product. Recovery of sodium compounds is important in the economy of the process. In modern kraft mills, operations are completely contained; waste streams are recycled and reused, eliminating water pollution.

Learn more about kraft process with a free trial on Britannica.com.

In printing, a technique of breaking up an image into a series of dots to permit reproduction of the full tone range of a photograph or artwork. It is traditionally done by placing a glass screen printed with a tight grid of lines over the plate being exposed. The grid breaks up the image into hundreds of tiny dots, each of which is read by the camera as either black or white—or, in the case of colour art, as either a single printing colour or white. The resulting image, called a halftone, is then rephotographed for printing. Screens are made with a varying number of lines per inch, depending on the application; for newspapers the range is about 80–120, whereas glossy magazines usually require 133–175 lines per inch.

Learn more about halftone process with a free trial on Britannica.com.

Legal proceedings carried out fairly and in accord with established rules and principles. Due process standards are sometimes referred to as either substantive or procedural. Substantive due process refers to a requirement that laws and regulations be related to a legitimate government interest (e.g., crime prevention) and not contain provisions that result in the unfair or arbitrary treatment of an individual. The 5th Amendment to the Constitution of the United States states that “no person shallelipsisbe deprived of life, liberty, or property, without due process of law.” This right was extended to the states by the 14th Amendment (1868). Fundamental to procedural due process are adequate notice before the government can deprive one of life, liberty, or property, and the opportunity to be heard and defend one's rights. The boundaries of due process are not fixed and are the subject of endless judicial interpretation and decision making. Seealso rights of the accused; double jeopardy.

Learn more about due process with a free trial on Britannica.com.

or MacArthur-Forrest process

Method of extracting silver and gold from their ores by dissolving them in a dilute solution of sodium cyanide or potassium cyanide. The process—invented in 1887 by the Scottish chemists John S. MacArthur, Robert W. Forrest, and William Forrest—includes contacting the finely ground ore with the cyanide solution, separating unwanted solids from the clear solution, and recovering the precious metals from the solution by precipitation with zinc dust.

Learn more about cyanide process with a free trial on Britannica.com.

Steelmaking method in which pure oxygen is blown through a long, movable lance into a bath of molten blast-furnace iron and scrap, in a steel furnace with a refractory lining called a converter. The oxygen initiates a series of heat-releasing reactions, including the oxidation of such impurities as silicon, carbon, phosphorus, and manganese; carbon dioxide is released, and the oxidation products of the other impurities form molten slag that floats on the molten steel. The advantages of using pure oxygen instead of air in refining iron into steel were recognized as early as the 1850s (see Bessemer process), but the process could not be commercialized until the late 1940s, when cheap, high-purity oxygen became available. Within 40 years it had replaced the open-hearth process and was producing more than half of all steel worldwide. Commercial advantages include high production rates, less labour, and steel with a low nitrogen content.

Learn more about basic oxygen process with a free trial on Britannica.com.

Modification of the Bessemer process for converting pig iron into steel. The original Bessemer converter was not effective in removing the phosphorus from iron made from the high-phosphorus ores common in Britain and Europe. The invention of the basic process in England by Sidney G. Thomas (1850–1885) and Percy Gilchrist overcame this problem; the Thomas-Gilchrist converter was lined with a basic material such as burned limestone rather than an acid siliceous material. The introduction of the basic Bessemer process in 1879 made it possible for the first time for such high-phosphorus ore to be used for making steel.

Learn more about basic Bessemer process with a free trial on Britannica.com.

or ammonia-soda process

Modern method of manufacturing sodium carbonate (soda ash), devised and commercialized in Belgium by Ernest Solvay (1838–1922). Common salt (sodium chloride) is treated with ammonia and then carbon dioxide, under carefully controlled conditions, to form sodium bicarbonate and ammonium chloride. When heated, the bicarbonate yields sodium carbonate, the desired product; the ammonium chloride is treated with lime to produce ammonia (for reuse) and calcium chloride. The process proved of great commercial value, since large quantities of soda ash are used in making glass, detergents, and cleansers. Seealso caustic soda.

Learn more about Solvay process with a free trial on Britannica.com.