Refrigeration is a process of moving heat from one location to another in controlled conditions. The work of heat transport is driven by mechanical work. Refrigeration has many applications, but not limited to, household refrigerators, industrial freezers, heat pumps may use the heat output of the refrigeration process, and may be designed to be reversible, but are otherwise similar to air conditioning units. Refrigeration has had a impact on industry, agriculture. The idea of preserving food dates back to at least the ancient Roman, mechanical refrigeration technology has rapidly evolved in the last century, from ice harvesting to temperature-controlled rail cars. Settlements were developing in parts of the country, filled with new natural resources. These new settlement patterns sparked the building of cities which are able to thrive in areas that were otherwise thought to be inhospitable, such as Houston and Las Vegas. In most developed countries, cities are heavily dependent upon refrigeration in supermarkets, the increase in food sources has led to a larger concentration of agricultural sales coming from a smaller percentage of existing farms.
Farms today have a larger output per person in comparison to the late 1800s. This has resulted in new food sources available to entire populations, the seasonal harvesting of snow and ice is an ancient practice estimated to have begun earlier than 1000 B. C. A Chinese collection of lyrics from this period known as the Shih king. However, little is known about the construction of these ice cellars or what the ice was used for. ”Historians have interpreted this to mean that the Jews used ice to cool beverages rather than to preserve food. Other ancient cultures such as the Greeks and the Romans dug large snow pits insulated with grass, like the Jews, the Greeks and Romans did not use ice and snow to preserve food, but primarily as a means to cool beverages. Slaves would moisten the outside of the jars and the resulting evaporation would cool the water, the ancient people of India used this same concept to produce ice. The Persians stored ice in a pit called a Yakhchal and may have been the first group of people to use storage to preserve food.
In the Australian outback before a reliable electricity supply was available where the weather could be hot and dry and this consisted of a room with hessian curtains hanging from the ceiling soaked in water. The water would evaporate and thereby cool the hessian curtains and thereby the air circulating in the room and this would allow many perishables such as fruit and cured meats to be kept that would normally spoil in the heat. Before 1830, few Americans used ice to refrigerate foods due to a lack of ice-storehouses and iceboxes, as these two things became more widely available, individuals used axes and saws to harvest ice for their storehouses
The melting point of a solid is the temperature at which it changes state from solid to liquid at atmospheric pressure. At the melting point the solid and liquid phase exist in equilibrium, the melting point of a substance depends on pressure and is usually specified at standard pressure. When considered as the temperature of the change from liquid to solid. Because of the ability of some substances to supercool, the point is not considered as a characteristic property of a substance. For most substances and freezing points are approximately equal, for example, the melting point and freezing point of mercury is 234.32 kelvins. However, certain substances possess differing solid-liquid transition temperatures, for example, agar melts at 85 °C and solidifies from 31 °C to 40 °C, such direction dependence is known as hysteresis. The melting point of ice at 1 atmosphere of pressure is close to 0 °C. In the presence of nucleating substances the freezing point of water is the same as the melting point, the chemical element with the highest melting point is tungsten, at 3687 K, this property makes tungsten excellent for use as filaments in light bulbs.
Many laboratory techniques exist for the determination of melting points, a Kofler bench is a metal strip with a temperature gradient. Any substance can be placed on a section of the strip revealing its thermal behaviour at the temperature at that point, differential scanning calorimetry gives information on melting point together with its enthalpy of fusion. A basic melting point apparatus for the analysis of crystalline solids consists of an oil bath with a transparent window, the several grains of a solid are placed in a thin glass tube and partially immersed in the oil bath. The oil bath is heated and with the aid of the melting of the individual crystals at a certain temperature can be observed. In large/small devices, the sample is placed in a heating block, the measurement can be made continuously with an operating process. For instance, oil refineries measure the point of diesel fuel online, meaning that the sample is taken from the process. This allows for more frequent measurements as the sample does not have to be manually collected, for refractory materials the extremely high melting point may be determined by heating the material in a black body furnace and measuring the black-body temperature with an optical pyrometer.
For the highest melting materials, this may require extrapolation by several hundred degrees, the spectral radiance from an incandescent body is known to be a function of its temperature. An optical pyrometer matches the radiance of a body under study to the radiance of a source that has been previously calibrated as a function of temperature, in this way, the measurement of the absolute magnitude of the intensity of radiation is unnecessary. However, known temperatures must be used to determine the calibration of the pyrometer, for temperatures above the calibration range of the source, an extrapolation technique must be employed
Tallow is a rendered form of beef or mutton fat, processed from suet. It is solid at room temperature, unlike suet, tallow can be stored for extended periods without the need for refrigeration to prevent decomposition, provided it is kept in an airtight container to prevent oxidation. In industry, tallow is not strictly defined as beef or mutton fat, in this context, tallow is animal fat that conforms to certain technical criteria, including its melting point. It is common for commercial tallow to contain fat derived from animals, such as lard from pigs. The diagram to the shows the chemical structure of a typical triglyceride molecule. Tallow is used mainly in producing soap and animal feed, tallow can be used for the production of biodiesel in much the same way as oils from plants are currently used. Because tallow is derived from animal by-products which have little to no value to food industries. The United States Air Force has experimented successfully with the use of tallow in aviation biofuels.
During five days of flight testing from August 23 to 27,2010, at Edwards Air Force Base, California, a significant use of tallow is for the production of shortening. It is one of the ingredients of Native American food called pemmican. Tallow is sometimes used in deep frying in place of other oils, before switching to pure vegetable oil in 1990, the McDonalds corporation cooked its French fries in a mixture of 93% beef tallow and 7% cottonseed oil. Many items of goods are produced from tallow, which was widely available domestically. Tallow can be used as flux for soldering and it is the primary ingredient in some leather conditioners. Tallow used to be used commonly in high-end shaving soaps, in particular those of elite British firms such as Geo, F Trumper, Truefitt & Hill, and Taylor of Old Bond Street. Tallow-based shaving soaps have enjoyed a resurgence in recent years due to gaining popularity of traditional wet-shaving, tallow has a use in printmaking where it is combined with bitumen and applied to metal print plates to provide a resist to acid etching.
The use of trace amounts of tallow as an additive to the used in polymer banknotes came to light in November 2016. Notes issued in 24 countries including Canada and the United Kingdom were found to be affected, leading to objections from vegans, in Leviticus 3, 14-17 the Israelites are forbidden to eat the suet surrounding certain internal organs of animals sacrificed at the Temple. This suet is Halakhically called chelev, tallow once was widely used to make moulded candles before more convenient wax varieties became available—and for some time after, as they continued to be a cheaper alternative
Colloquially, room temperature is the range of temperatures that people prefer for indoor settings, at which the air feels neither hot nor cold when wearing typical indoor clothing. The range is typically between 15 °C and 25 °C and various methods of control are often employed to maintain this thermal comfort level. In certain fields, like science and engineering, and within a particular context, the American Heritage Dictionary of the English Language identifies room temperature as around 20 to 22 °C. Ambient temperature simply means the temperature of the surroundings and will be the same as room temperature indoors, standard conditions for temperature and pressure
The kilogram or kilogramme is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype of the Kilogram. The avoirdupois pound, used in both the imperial and US customary systems, is defined as exactly 0.45359237 kg, making one kilogram approximately equal to 2.2046 avoirdupois pounds. Other traditional units of weight and mass around the world are defined in terms of the kilogram, the gram, 1/1000 of a kilogram, was provisionally defined in 1795 as the mass of one cubic centimeter of water at the melting point of ice. The final kilogram, manufactured as a prototype in 1799 and from which the IPK was derived in 1875, had an equal to the mass of 1 dm3 of water at its maximum density. The kilogram is the only SI base unit with an SI prefix as part of its name and it is the only SI unit that is still directly defined by an artifact rather than a fundamental physical property that can be reproduced in different laboratories.
Three other base units and 17 derived units in the SI system are defined relative to the kilogram, only 8 other units do not require the kilogram in their definition, temperature and frequency, and angle. At its 2011 meeting, the CGPM agreed in principle that the kilogram should be redefined in terms of the Planck constant, the decision was originally deferred until 2014, in 2014 it was deferred again until the next meeting. There are currently several different proposals for the redefinition, these are described in the Proposed Future Definitions section below, the International Prototype Kilogram is rarely used or handled. In the decree of 1795, the term gramme thus replaced gravet, the French spelling was adopted in the United Kingdom when the word was used for the first time in English in 1797, with the spelling kilogram being adopted in the United States. In the United Kingdom both spellings are used, with kilogram having become by far the more common, UK law regulating the units to be used when trading by weight or measure does not prevent the use of either spelling.
In the 19th century the French word kilo, a shortening of kilogramme, was imported into the English language where it has used to mean both kilogram and kilometer. In 1935 this was adopted by the IEC as the Giorgi system, now known as MKS system. In 1948 the CGPM commissioned the CIPM to make recommendations for a practical system of units of measurement. This led to the launch of SI in 1960 and the subsequent publication of the SI Brochure, the kilogram is a unit of mass, a property which corresponds to the common perception of how heavy an object is. Mass is a property, that is, it is related to the tendency of an object at rest to remain at rest, or if in motion to remain in motion at a constant velocity. Accordingly, for astronauts in microgravity, no effort is required to hold objects off the cabin floor, they are weightless. However, since objects in microgravity still retain their mass and inertia, the ratio of the force of gravity on the two objects, measured by the scale, is equal to the ratio of their masses.
On April 7,1795, the gram was decreed in France to be the weight of a volume of pure water equal to the cube of the hundredth part of the metre
In chemistry, a soap is a salt of a fatty acid. Household uses for soaps include washing and other types of housekeeping, in industry they are used in textile spinning and are important components of some lubricants. Metal soaps are included in modern artists oil paints formulations as a rheology modifier, soaps for cleaning are obtained by treating vegetable or animal oils and fats with a strong base, such as sodium hydroxide or potassium hydroxide in an aqueous solution. Fats and oils are composed of triglycerides, three molecules of fatty acids attach to a molecule of glycerol. The alkaline solution, which is often called lye, induces saponification, the glycerin, a useful byproduct, can remain in the soap product as a softening agent, or be isolated for other uses. Soaps are key components of most lubricating greases, which are usually emulsions of calcium soap or lithium soap, many other metallic soaps are useful, including those of aluminium and mixtures of them. Such soaps are used as thickeners to increase the viscosity of oils, in ancient times, lubricating greases were made by the addition of lime to olive oil.
When used for cleaning, soap allows insoluble particles to become soluble in water, for example, oil/fat is insoluble in water, but when a couple of drops of dish soap are added to the mixture, the oil/fat solubilizes into the water. Anything that is soluble will be washed away with the water, the type of alkali metal used determines the kind of soap product. Sodium soaps, prepared from sodium hydroxide, are firm, whereas potassium soaps, potassium hydroxide was extracted from the ashes of bracken or other plants. Lithium soaps tend to be hard—these are used exclusively in greases, soaps are derivatives of fatty acids. Traditionally they have made from triglycerides. Triglyceride is the name for the triesters of fatty acids. Tallow, i. e. rendered beef fat, is the most available triglyceride from animals and its saponified product is called sodium tallowate. Typical vegetable oils used in soap making are palm oil, coconut oil, olive oil, each species offers quite different fatty acid content and hence, results in soaps of distinct feel.
The seed oils give softer but milder soaps, Soap made from pure olive oil is sometimes called Castile soap or Marseille soap, and is reputed for being extra mild. The term Castile is applied to soaps from a mixture of oils. The earliest recorded evidence of the production of soap-like materials dates back to around 2800 BC in ancient Babylon, a formula for soap consisting of water and cassia oil was written on a Babylonian clay tablet around 2200 BC
Chelev is the term given to some kinds of animal fats in Judaism. There is a prohibition in the Torah for Jews and Israelites against eating chelev, only the chelev of animals that are of the sort from which offerings can be brought in the Tabernacle or Temple are prohibited. The prohibition of eating chelev is also, in addition to the Torah, one of the 613 commandments that, speak to the Children of Israel, You shall not eat any fat of an ox, sheep, or goat. The fat of carrion and the fat of an animal with a disease or injury, may be used for any work. In the Hebrew language the word for fat is and it is first used for the fats of Abels offering, the same word is used in the phrase the fat of the land. The punishment for eating chelev bemeizid is kareth, the atonement for eating it by mistake is to bring a korban hattath. The prohibition on chelev is only regarding those animal types which were used as a korban, cattle and goat, fats from avians and deer may be eaten, and different types of bovinae are in state of doubt.
In order that fat should be considered chelev it must look like a sheet of fats, some tendons and muscles are removed due to the rabbinic law, since they are neighboring and resolving some chelev. The chelev must be removed by a qualified menaker in a process called nikkur, the fats surrounding the kidneys are called chelev hakloyoth, and are considered non-kosher. The sheet of fat which is covering the interior of the cavity is real chelev, except at some regions where it is covered with steak. However even where it is covered with meat, there is some fat which is still forbidden, one must be well trained in order to identify kosher fat. There are many fats around the organs such as the stomach and intestines. The tail fat of the sheep, called alyah in Hebrew, is a large fatty membrane located on the hindquarters of certain breeds of sheep. The written Torah uses the term cheilev of this fat, but only in the sense of the good part, karaite Jews maintain that the alyah, too, is prohibited. Laws of Judaism concerning eating fat from the Torah and Maimonides’ Code of Jewish Law Getting the Knack of Nikkur, OU Kashrut Seminar on Removing Veins and Forbidden Fat Big Success OU Film
Wendys is an American international fast food restaurant chain founded by Dave Thomas on November 15,1969, in Columbus, United States. The company moved its headquarters to Dublin, Ohio, on January 29,2006, as of 2016, Wendys was the worlds third largest hamburger fast food chain with 6,537 locations, following Burger Kings 15,738 locations and McDonalds 36,615 locations. On April 24,2008, the company announced a merger with Triarc Companies Inc. a publicly traded company, despite the new ownership, Wendys headquarters remained in Dublin. Previously, Wendys had rejected more than two buyout offers from Triarc, following the merger, Triarc became known as Wendys/Arbys Group, and as The Wendys Company. As of January 2,2017, there were a total of 6,537 locations,6,207 restaurants are franchised, and 77% of them are located in North America. Wendys and its affiliates more than 47,000 people in its global operations. In fiscal year 2006, the firm had $2.469 billion in total sales, while Wendys sets standards for exterior store appearance, food quality, and menu, individual owners have control over hours of operations, interior decor and staff uniforms and wages.
Wendys menu consists primarily of hamburgers, chicken sandwiches, French fries and beverages, including the signature Frosty, Single, a square-pattied burger made with fresh ground beef rather than round frozen patties. Wendys uses these square hamburger patties – which hang over the edge of a circular bun – as its signature item, the chain is known for its square hamburgers, sea salt fries and the Frosty, a form of soft serve ice cream mixed with frozen starches. The idea for Wendys old fashioned hamburgers was inspired by Dave Thomass trips to Kewpee Hamburgers in his town of Kalamazoo. The Kewpee sold square hamburgers and thick malt shakes, much like the restaurant that Thomas eventually founded in Columbus, Ohio. Square patties had corners that stuck out so that customers could see the quality of the meat. The Columbus location added a Tim Hortons and was closed on March 2,2007, Thomas named the restaurant after his fourth child Melinda Lou Wendy Thomas. Photographs of her were on display at the original Wendys restaurant until it closed, in August 1972, the first Wendys franchisee, L. S.
Hartzog, signed an agreement for Indianapolis, also, in 1972, Wendys aired its first TV commercials that were only broadcast locally in Ohio. The first Canadian restaurant opened in Hamilton, ON in 1976, in December 1976, Wendys opened its 500th restaurant, located in Toronto, Canada. Wendys founded the fried chicken chain Sisters Chicken in 1978 and sold it to its largest franchiser in 1987, in 1979, the first European Wendys opened in Munich. The same year Wendys became the first fast-food chain to introduce the salad bar, Wendys entered the Asian market by opening its first restaurants in Japan in 1980, in Hong Kong in 1982 and in the Philippines and Singapore in 1983
Burger King is an American global chain of hamburger fast food restaurants. Headquartered in the area of Miami-Dade County, the company was founded in 1953 as InstaBurger King. After Insta-Burger King ran into difficulties in 1954, its two Miami-based franchisees David Edgerton and James McLamore purchased the company and renamed it Burger King. In late 2010, 3G Capital of Brazil acquired a majority stake in the company, the new owners promptly initiated a restructuring of the company to reverse its fortunes. The 1970s were the Golden Age of the advertising, but beginning in the early-1980s. A series of less successful advertising campaigns created by a procession of advertising agencies continued for the two decades. While highly successful, some of CP+Bs commercials were derided for perceived sexism or cultural insensitivity, Burger Kings menu has expanded from a basic offering of burgers, French fries and milkshakes to a larger and more diverse set of products. In 1957, the Whopper became the first major addition to the menu, conversely, BK has introduced many products, which failed to catch hold in the marketplace.
Some of these failures in the United States have seen success in foreign markets, from 2002 to 2010, Burger King aggressively targeted the 18–34 male demographic with larger products that often carried correspondingly large amounts of unhealthy fats and trans-fats. This tactic would eventually damage the financial underpinnings, and cast a negative pall on its earnings. As of December 31,2016, Burger King reported it had 15,738 outlets in 100 countries. Of these,47. 5% are in the United States and 99. 5% are privately owned and operated, BK has historically used several variations of franchising to expand its operations. Burger Kings relationship with its franchises has not always been harmonious, occasional spats between the two have caused numerous issues, and in several instances, the companys and its licensees relations have degenerated into precedent-setting court cases. Burger Kings Australian franchise Hungry Jacks is the franchise to operate under a different name, due to a trademark dispute.
The predecessor to Burger King was founded in 1953 in Jacksonville and their production model was based on one of the machines they had acquired, an oven called the Insta-Broiler. This strategy proved to be so successful that required all of their franchises to use the device. After the company faltered in 1959, it was purchased by its Miami, franchisees, James McLamore and they initiated a corporate restructuring of the chain, first renaming the company Burger King. They ran the company as an independent entity for eight years, pillsburys management tried several times to restructure Burger King during the late 1970s and the early 1980s
Roark Capital Group acquired the company in July 2011 and owns 81. 5% of the company, with The Wendys Company owning the other 18. 5%. In addition to its classic Roast Beef and Beef n Cheddar sandwiches, Arbys products include deli-style Market Fresh line of sandwiches, Curly Fries and its headquarters are in Sandy Springs, Georgia. As of December 31,2015, there were 3,342 restaurants, there are international locations in four countries outside of the United States, Turkey and United Arab Emirates. The brothers wanted to call their restaurants Big Tex, but that name was used by an Akron business. Instead, they chose the name Arbys, based on R. B. the initials of Raffel Brothers, the Raffel brothers opened the first new restaurant in Boardman, just outside Youngstown, on July 23,1964. They initially served only roast beef sandwiches, potato chips, hoping to attract a more upscale clientele, Arbys interior design was purposely more luxurious in appearance than the typical fast food sandwich stand of the day.
Arbys offered their roast beef sandwiches for $.69 at a time when hamburger stands were charging $.15 for a hamburger, a year later, the first Arbys licensee opened a restaurant in Akron, Ohio. The famous Arbys hat was designed by the original sign makers, expansion to other states began in 1968, beginning in Pittsburgh and Detroit. During the 1970s, the expansion of Arbys took place at a rate of 50 stores per year. During this time it created several menu items, including the Beef n Cheddar, Jamocha Shakes, chicken sandwiches, Curly Fries, baked potatoes were added to the menu in 1968. Curly Fries were initially introduced as Curly-Q Fries in 1988 and it became the first restaurant in the fast food industry to offer a complete lite menu in 1991 with several sandwiches and salads under 300 calories and 94 percent fat-free. The family-owned business tried converting into a company in 1970 by the offering the sale of stock. In 1976, the sold the company to Royal Crown Cola Company for $18 million.
In 1984, Victor Posner obtained Arbys via a takeover of its parent Royal Crown through his DWG Corporation. Nine years later, with a new owner of DWG Corporation, with $100 million additional funding, Pierce moved to a new Roast Town concept, similar in format to Boston Market, in 1996. The Roast Town concept received poor marks in market tests and was quickly discontinued and his team left the company and it sold all of its 354 company-owned locations to RTM Restaurant Group, an existing Arbys franchise, for $71 million. Another marketing concept that was tried was a venture that was started in 1995 with ZuZus Handmade Mexican Grill. The marketing venture was a failure resulting in lawsuits being filed by each company against the other, Inc. opened the first Arbys franchise in the Canadian province of Quebec
Dairy Queen, often abbreviated DQ, is a chain of soft serve ice cream and fast food restaurants owned by International Dairy Queen, Inc, a subsidiary of Berkshire Hathaway. International Dairy Queen, Inc. owns Orange Julius and Karmelkorn, the first DQ restaurant was located in Joliet, Illinois. It was operated by Sherb Noble and opened for business on June 22,1940 and it served a variety of frozen products, such as soft serve ice cream. The companys corporate offices are located in the Minneapolis suburb of Edina, the soft-serve formula was first developed in 1938 by Douds, Iowa-born John Fremont J. F. Grandpa McCullough and his son Alex. They convinced friend and loyal customer Sherb Noble to offer the product in his ice cream store in Kankakee, on the first day of sales, Noble dished out more than 1,600 servings of the new dessert within two hours. Noble and the McCulloughs went on to open the first Dairy Queen store in 1940 in Joliet, while this Dairy Queen has not been in operation since the 1950s, the building still stands at 501 N Chicago St. as a city-designated landmark.
Since 1940, the chain has used a system to expand its operations globally. In the US, the state with the most Dairy Queen restaurants is Texas, International Dairy Queen, Inc. is the parent company of Dairy Queen. In the United States, it operates under American Dairy Queen Corp, IDQ is a wholly owned subsidiary of Berkshire Hathaway. At the end of its fiscal year 2014, Dairy Queen reported over 6,400 stores in more than 25 countries, about 4,500 of its stores were located in the United States. DQ was a pioneer of food franchising, expanding its 10 stores in 1941 to 100 by 1947,1,446 in 1950. The first store in Canada opened in Melville, Saskatchewan, in 1953, the red Dairy Queen symbol was introduced in 1959. The company became International Dairy Queen, Inc. in 1962, in 1987, IDQ bought the Orange Julius chain. IDQ was acquired by Berkshire Hathaway in 1998, Dairy Queens were a fixture of social life in small towns of the Midwestern and Southern United States during the 1950s and 1960s. The companys stores are operated under several brands, all bearing the distinctive Dairy Queen logo, in the 1970s, most restaurants were Brazier locations with a second floor for storage, recognizable for their red mansard roofs.
As of the end of 2014, Dairy Queen had more than 6,400 stores in 27 countries, including more than 1,400 locations outside the United States, the largest Dairy Queen in the United States is located in Bloomington, Illinois. The busiest store in the United States is in Rosedale, the largest store in the world was built in Riyadh, Saudi Arabia. The busiest store in the world is located in Charlottetown, Prince Edward Island, so-called Limited Brazier locations may additionally offer hot dogs, barbecue beef sandwiches, and in some cases french fries and chicken, but not hamburgers
Selenium is a chemical element with symbol Se and atomic number 34. It is a nonmetal with properties that are intermediate between the elements above and below in the table and tellurium. It rarely occurs in its state or as pure ore compounds in the Earths crust. Selenium was discovered in 1817 by Jöns Jacob Berzelius, who noted the similarity of the new element to the previously discovered tellurium, Selenium is found in metal sulfide ores, where it partially replaces the sulfur. Commercially, selenium is produced as a byproduct in the refining of these ores, minerals that are pure selenide or selenate compounds are known but rare. The chief commercial uses for selenium today are glassmaking and pigments, Selenium is a semiconductor and is used in photocells. Applications in electronics, once important, have been supplanted by silicon semiconductor devices. Selenium is still used in a few types of DC power surge protectors, Selenium salts are toxic in large amounts, but trace amounts are necessary for cellular function in many organisms, including all animals.
Selenium is an ingredient in multivitamins and other dietary supplements. It is a component of the antioxidant enzymes glutathione peroxidase and thioredoxin reductase and it is found in three deiodinase enzymes, which convert one thyroid hormone to another. Selenium requirements in plants differ by species, with some plants requiring relatively large amounts, Selenium forms several allotropes that interconvert with temperature changes, depending somewhat on the rate of temperature change. When prepared in chemical reactions, selenium is usually an amorphous, when rapidly melted, it forms the black, vitreous form, usually sold commercially as beads. The structure of black selenium is irregular and complex and consists of rings with up to 1000 atoms per ring. Black Se is a brittle, lustrous solid that is soluble in CS2. Upon heating, it softens at 50 °C and converts to gray selenium at 180 °C, the red α, β, and γ forms are produced from solutions of black selenium by varying the evaporation rate of the solvent.
They all have low, monoclinic crystal symmetries and contain nearly identical puckered Se8 rings with different arrangements. The packing is most dense in the α form, in the Se8 rings, the Se-Se distance is 233.5 pm and Se-Se-Se angle is 105. 7°. Other selenium allotropes may contain Se6 or Se7 rings, the most stable and dense form of selenium is gray and has a hexagonal crystal lattice consisting of helical polymeric chains, where the Se-Se distance is 237.3 pm and Se-Se-Se angle is 130. 1°