A refrigerator (colloquially fridge) is a common household appliance that consists of a thermally insulated compartment and a heat pump (mechanical, electronic, or chemical) that transfers heat from the inside of the fridge to its external environment so that the inside of the fridge is cooled to a temperature below the ambient temperature of the room. Refrigeration is an essential food storage technique in developed countries. Lower temperatures in a confined volume lowers the reproduction rate of bacteria, so the refrigerator reduces the rate of spoilage.
A refrigerator maintains a temperature a few degrees above the freezing point of water. Optimum temperature range for perishable food storage is 3 to 5 °C (37 to 41 °F). A similar device that maintains a temperature below the freezing point of water is called a freezer. The refrigerator replaced the icebox, which was a common household appliance for almost a century and a half prior. For this reason, a refrigerator is sometimes referred to as an icebox.
Freezer units are used in households and in industry and commerce. Food stored at or below is safe indefinitely. Most household freezers maintain temperatures from -23 to -18 °C (-9 to -0 °F), although some freezer-only units can achieve and lower. Refrigerators generally do not achieve lower than , since the same coolant loop serves both compartments: Lowering the freezer compartment temperature excessively causes difficulties in maintaining above-freezing temperature in the refrigerator compartment. Domestic freezers can be included as a separate compartment in a refrigerator, or can be a separate appliance. Domestic freezers are generally upright units resembling refrigerators, or chests (resembling upright units laid on their backs). Many upright modern freezers come with an ice dispenser built into their door. Some even more upright and new models include exact temperature changing devices and even a built in clock.
Commercial refrigerator and freezer units, which go by many other names, were in use for almost 40 years prior to the common home models. They used gas systems such as anhydrous ammonia (R-717) or sulfur dioxide (R-764), which occasionally leaked, making them unsafe for home use and industrial purposes. Practical household refrigerators were introduced in 1915 and gained wider acceptance in the United States in the 1930s as prices fell and non-toxic, non-flammable synthetic refrigerants such as Freon-12® (R-12) were introduced. However, R-12 damaged the ozone layer, causing governments to issue a ban on its use in new refrigerators and air-conditioning systems in 1994. The less harmful replacement for R-12, R-134a (tetrafluoroethane), has been in common use since 1990, but R-12 is still found in many old systems today.
Most households][ use the freezer-on-top-and-refrigerator-on-bottom style, which has been the basic style since the 1940s.
In the early 1950s most refrigerators were white, but from the mid-1950s through present day designers and manufacturers put color onto refrigerators. In the late-1950s/early-1960s, pastel colors like turquoise and pink became popular, brushed chrome-plating (similar to stainless finish) was available on some models from different brands. In the late 1960s and throughout the 1970s, earth toned colors were popular, including Harvest Gold, Avocado Green and almond. In the 1980s, black was viewed as luxurious. In the late 1990s stainless steel became stylish, and in 2009, one manufacturer introduced multi-color designs.
Most home refrigerators weigh between 200 pounds (91 kg) and 450 pounds (200 kg), with some models weighing up to 875 pounds (397 kg).
Before the invention of the refrigerator, icehouses were used to provide cool storage for most of the year. Placed near freshwater lakes or packed with snow and ice during the winter, they were once very common. Natural means are still used to cool foods today. On mountainsides, runoff from melting snow is a convenient way to cool drinks, and during the winter one can keep milk fresh much longer just by keeping it outdoors.
In the 11th century, Persian physicist and chemist Ibn Sina (Latinized name: Avicenna) invented the refrigerated coil, which condenses aromatic vapours.][ This was a breakthrough in distillation technology and he made use of it in his steam distillation process, which requires refrigerated tubing, to produce essential oils.][
The first known artificial refrigeration was demonstrated by William Cullen at the University of Glasgow in 1748. The American inventor Oliver Evans, acclaimed as the "father of refrigeration," invented the vapor-compression refrigeration machine in 1805. Heat was removed from the environment by recycling vaporized refrigerant, where it moved through a compressor and condenser, where it eventually reverted to a liquid form to repeat the process. However, Evans built no such refrigeration unit. In 1834, Jacob Perkins modified Evans' original design, building the world's first refrigerator and filing the first legal patent for refrigeration using vapor-compression. John Gorrie, an American doctor from Florida, invented the first mechanical refrigeration unit in 1841—based on Evans' original invention to make ice in—to cool air for yellow fever patients. Gorrie's mechanical refrigeration unit received a patent in 1851. American professor Alexander C. Twining of Cleveland, Ohio patented an early vapor-compression refrigerator in 1853 that was fully capable of producing a ton of ice per day.
In 1856, James Harrison, an immigrant from Scotland living in Australia, developed an ice making machine using ammonia and an ether compressor. It was used in the brewing and meat packing industries of Geelong, Victoria. Ferdinand Carré of France developed a somewhat more complex system in 1859. Unlike earlier compression-compression machines, which used air as a coolant, Carré's equipment contained rapidly expanding ammonia. In 1867, Andrew Muhl, an immigrant from France, built an ice-making machine in San Antonio, Texas, to help service the expanding beef industry before moving it to Waco in 1871. In 1873, the patent for this machine was contracted by the Columbus Iron Works, a company acquired by the W. C. Bradley Co., which produced the world's first commercial ice-makers.
Carl Paul Gottfried Linde, ennobled in 1897 as Ritter von Linde, was a German engineer who developed refrigeration and gas separation technologies. In 1890, Carl von Linde moved back to Munich where he took up his professorship once more, but was soon back at work developing new refrigeration cycles. In 1892, an order from the Guinness brewery in Dublin for a Carbon Dioxide liquefaction plant drove Linde's research into the area of low temperature refrigeration, and in 1894 he started work on a process for the liquefaction of air. In 1895, Linde first achieved success, and filed for patent protection of his process (not approved in the US until 1903). In 1901, Linde began work on a technique to obtain pure oxygen and nitrogen based on the fractional distillation of liquefied air. By 1910 coworkers including Carl's son Friedrich had developed the Linde double-column process, variants of which are still in common use today.
In 1913, refrigerators for home and domestic use were invented by Fred W. Wolf of Fort Wayne, Indiana with models consisting of a unit that was mounted on top of an ice box. In 1914, engineer Nathaniel B. Wales of Detroit, Michigan, introduced an idea for a practical electric refrigeration unit, which later became the basis for the Kelvinator. A self-contained refrigerator, with a compressor on the bottom of the cabinet was invented by Alfred Mellowes in 1916. Mellowes produced this refrigerator commercially but was bought out by William C. Durant in 1918, who started the Frigidaire Company to mass-produce refrigerators. In 1918, Kelvinator Company introduced the first refrigerator with any type of automatic control. The absorption refrigerator was invented by Baltzar von Platen and Carl Munters from Sweden in 1922, while they were still students at the Royal Institute of Technology in Stockholm. It became a worldwide success and was commercialized by Electrolux. Other pioneers included Charles Tellier, David Boyle, and Raoul Pictet. Carl von Linde was the first to patent and make a practical and compact refrigerator.
These home units usually required the installation of the mechanical parts, motor and compressor, in the basement or an adjacent room while the cold box was located in the kitchen. There was a 1922 model that consisted of a wooden cold box, water-cooled compressor, an ice cube tray and a 9-cubic-foot (0.25 m3) compartment, and cost $714. (A 1922 Model-T Ford cost about $450.) By 1923, Kelvinator held 80 percent of the market for electric refrigerators. Also in 1923 Frigidaire introduced the first self-contained unit. About this same time porcelain-covered metal cabinets began to appear. Ice cube trays were introduced more and more during the 1920s; up to this time freezing was not an auxiliary function of the modern refrigerator.
The first refrigerator to see widespread use was the General Electric "Monitor-Top" refrigerator introduced in 1927, so-called because of its resemblance to the gun turret on the ironclad warship MonitorUSS of the 1860s. The compressor assembly, which emitted a great deal of heat, was placed above the cabinet, and surrounded with a decorative ring. Over a million units were produced. As the refrigerating medium, these refrigerators used either sulfur dioxide, which is corrosive to the eyes and may cause loss of vision, painful skin burns and lesions, or methyl formate, which is highly flammable, harmful to the eyes, and toxic if inhaled or ingested. Many of these units are still functional today. These cooling systems cannot legally be recharged with the hazardous original refrigerants if they leak or break down.][
The introduction of Freon in the 1920s expanded the refrigerator market during the 1930s and provided a safer, low-toxicity alternative to previously used refrigerants. Separate freezers became common during the 1940s, the popular term at the time for the unit was a deep freeze. These devices, or appliances, did not go into mass production for use in the home until after World War II. The 1950s and 1960s saw technical advances like automatic defrosting and automatic ice making. More efficient refrigerators were developed in the 1970s and 1980s, even though environmental issues led to the banning of very effective (Freon) refrigerants. Early refrigerator models (from 1916) had a cold compartment for ice cube trays. From the late 1920s fresh vegetables were successfully processed through freezing by the Postum Company (the forerunner of General Foods), which had acquired the technology when it bought the rights to Clarence Birdseye's successful fresh freezing methods.
The first successful application of frozen foods occurred when General Foods heiress Marjorie Merriweather Post (then wife of Joseph E. Davies, United States Ambassador to the Soviet Union) deployed commercial-grade freezers in Spaso House, the US Embassy in Moscow, in advance of the Davies’ arrival. Post, fearful of the USSR's food processing safety standards, fully stocked the freezers with products from General Foods' Birdseye unit. The frozen food stores allowed the Davies to entertain lavishly and serve fresh frozen foods that would otherwise be out of season. Upon returning from Moscow, Post (who resumed her maiden name after divorcing Davies) directed General Foods to market frozen product to upscale restaurants.
Home freezers as separate compartments (larger than necessary just for ice cubes), or as separate units, were introduced in the United States in 1940. Frozen foods, previously a luxury item, became commonplace.
A vapor compression cycle is used in most household refrigerators, refrigerator–freezers and freezers. In this cycle, a circulating refrigerant such as R134a enters a compressor as low-pressure vapor at or slightly above the temperature of the refrigerator interior. The vapor is compressed and exits the compressor as high-pressure superheated vapor. The superheated vapor travels under pressure through coils or tubes comprising the condenser, which are passively cooled by exposure to air in the room. The condenser cools the vapor, which liquefies. As the refrigerant leaves the condenser, it is still under pressure but is now only slightly above room temperature. This liquid refrigerant is forced through a metering or throttling device, also known as an expansion valve (essentially a pin-hole sized constriction in the tubing) to an area of much lower pressure. The sudden decrease in pressure results in explosive-like flash evaporation of a portion (typically about half) of the liquid. The latent heat absorbed by this flash evaporation is drawn mostly from adjacent still-liquid refrigerant, a phenomenon known as auto-refrigeration. This cold and partially vaporized refrigerant continues through the coils or tubes of the evaporator unit. A fan blows air from the refrigerator or freezer compartment ("box air") across these coils or tubes and the refrigerant completely vaporizes, drawing further latent heat from the box air. This cooled air is returned to the refrigerator or freezer compartment, and so keeps the box air cold. Note that the cool air in the refrigerator or freezer is still warmer than the refrigerant in the evaporator. Refrigerant leaves the evaporator, now fully vaporized and slightly heated, and returns to the compressor inlet to continue the cycle.
An absorption refrigerator works differently from a compressor refrigerator, using a source of heat, such as combustion of liquefied petroleum gas, solar thermal energy or an electric heating element. These heat sources are much quieter than the compressor motor in a typical refrigerator. A fan or pump might be the only mechanical moving parts; reliance on convection is considered impractical.
The Peltier effect uses electricity to pump heat directly; this type of refrigerator is sometimes used for camping, or where noise is not acceptable. They can be totally silent (if they don't include a fan for air circulation) but are less energy-efficient than other methods.
Other uses of an absorption refrigerator (or "chiller") include large systems used in office buildings or complexes such as hospitals and universities. These large systems are used to chill a brine solution that is circulated through the building.
Many modern refrigerator/freezers have the freezer on top and the refrigerator on the bottom. Most refrigerator-freezers—except for manual defrost models or cheaper units—use what appears to be two thermostats. Only the refrigerator compartment is properly temperature controlled. When the refrigerator gets too warm, the thermostat starts the cooling process and a fan circulates the air around the freezer. During this time, the refrigerator also gets colder. The freezer control knob only controls the amount of air that flows into the refrigerator via a damper system. Changing the refrigerator temperature will inadvertently change the freezer temperature in the opposite direction. Changing the freezer temperature will have no effect on the refrigerator temperature. The freezer control may also be adjusted to compensate for any refrigerator adjustment.
This means the refrigerator may become too warm. However, because only enough air is diverted to the refrigerator compartment, the freezer usually re-acquires the set temperature quickly, unless the door is opened. When a door is opened, either in the refrigerator or the freezer, the fan in some units stops immediately to prevent excessive frost build up on the freezer's evaporator coil, because this coil is cooling two areas. When the freezer reaches temperature, the unit cycles off, no matter what the refrigerator temperature is. Some people][ recommend setting the refrigerator to maximum and the freezer to a point where one's refrigerated food won't freeze. Modern computerized refrigerators do not use the damper system. The computer manages fan speed for both compartments, although air is still blown from the freezer.
Alternatives to the vapor-compression cycle not in current use include:
Newer refrigerators may include:
Early freezer units accumulated ice crystals around the freezing units. This was a result of humidity introduced into the units when the doors to the freezer were opened condensing on the cold parts, then freezing. This frost buildup required periodic thawing ("defrosting") of the units to maintain their efficiency. Manual Defrost (referred to as Cyclic) units are still available. Advances in automatic defrosting eliminating the thawing task were introduced in the 1950s, but are not universal, due to energy performance and cost. These units used a counter that only defrosted the freezer compartment (Freezer Chest) when a specific number of door openings had been made. The units were just a small timer combined with an electrical heater wire that heated the freezer's walls for a short amount of time to remove all traces of frost/frosting. Also, early units featured freezer compartments located within the larger refrigerator, and accessed by opening the refrigerator door, and then the smaller internal freezer door; units featuring an entirely separate freezer compartment were introduced in the early 1960s, becoming the industry standard by the middle of that decade. These older freezer compartments were the main cooling body of the refrigerator, and only maintained a temperature of around , which is suitable for keeping food for a week.
Later advances included automatic ice units and self compartmentalized freezing units.
An increasingly important environmental concern is the disposal of old refrigerators— initially because freon coolant damages the ozone layer—but as older generation refrigerators wear out, the destruction of CFC-bearing insulation also causes concern. Modern refrigerators usually use a refrigerant called HFC-134a (1,1,1,2-Tetrafluoroethane), which does not deplete the ozone layer, instead of Freon. A R-134a is now becoming very uncommon in Europe. Newer refrigerants are being used instead. The main refrigerant now used is R-600a, or isobutane. This refrigerant is naturally occurring, and has a smaller effect on the atmosphere if released. There have been reports of refrigerators exploding if the refrigerant leaks gas in the presence of a spark.
Disposal of discarded refrigerators is regulated, often mandating the removal of doors; children playing hide-and-seek have been asphyxiated while hiding inside discarded refrigerators, particularly older models with latching doors. Since August 2, 1956, under U.S. federal law, refrigerator doors are no longer permitted to lock from the inside. More modern units use a magnetic door gasket that holds the door sealed but can be pushed open from the inside. This gasket was invented by Herman C. Ells Sr.
Domestic refrigerators and freezers for food storage are made in a range of sizes. Among the smallest is a 4 L Peltier refrigerator advertised as being able to hold 6 cans of beer. A large domestic refrigerator stands as tall as a person and may be about 1 m wide with a capacity of 600 L. Some models for small households fit under kitchen work surfaces, usually about 86 cm high. Refrigerators may be combined with freezers, either stacked with refrigerator or freezer above, below, or side by side. A refrigerator without a frozen food storage compartment may have a small section just to make ice cubes. Freezers may have drawers to store food in, or they may have no divisions (chest freezers).
Refrigerators and freezers may be free-standing, or built into a kitchen.
Other specialised cooling mechanisms may be used for cooling, but have not been applied to domestic refrigerators.
In the past, refrigerators consumed more energy than any other home appliance][, but in the last 20 years progress has been made to design, manufacture, and encourage the sale of refrigerators with improved energy efficiency. In the early 1990s a competition was held among the major manufacturers to encourage energy efficiency. Current US models that are Energy Star qualified use 50 percent less energy than the average models made in 1974. The most energy-efficient unit made in the US consumes about half a kilowatt-hour per day (20 W). But even ordinary units are quite efficient; some smaller units use less than 0.2 kWh per day (8 W). Larger units, especially those with large freezers and icemakers, may use as much as 4 kW·h per day (170 W). The European Union uses a letter-based mandatory energy efficiency rating label instead of the Energy Star; thus EU refrigerators at the point of sale are labelled according to how energy-efficient they are.
For US refrigerators, the Consortium on Energy Efficiency (CEE) further differentiates between Energy Star qualified refrigerators. Tier 1 refrigerators are those that are 20% to 24.9% more efficient than the Federal minimum standards set by the National Appliance Energy Conservation Act (NAECA). Tier 2 are those that are 25% to 29.9% more efficient. Tier 3 is the highest qualification, for those refrigerators that are at least 30% more efficient than Federal standards. About 82% of the Energy Star qualified refrigerators are Tier 1, with 13% qualifying as Tier 2, and just 5% at Tier 3.
Besides the standard style of compressor refrigeration used in normal household refrigerators and freezers, there are technologies such as absorption refrigeration and magnetic refrigeration. Although these designs generally use a much larger amount of energy compared to compressor refrigeration, other qualities such as silent operation or the ability to use gas can favor these refrigeration units in small enclosures, a mobile environment or in environments where unit failure would lead to devastating consequences.
Among the different models of refrigerators, top-freezer models are more efficient than bottom-freezer models of the same capacity, which are in turn more efficient than side-freezer models. Models with through-the-door ice units are less efficient than those without. Dr. Tom Chalko in Australia has developed an external thermostat to convert any][ chest freezer into a chest refrigerator using only about 0.1kWh per day—the amount of energy used by a 100 watt light bulb in one hour. A similar device is manufactured by Johnson Controls. Scientists at Oxford University have reconstructed a refrigerator invented in 1930 by Leó Szilárd and Albert Einstein in their efforts to replace current technologies with energy efficient green technology. The Einstein refrigerator operates without electricity and uses no moving parts or greenhouse gases.
Many refrigerators made in the 1930s and 1940s were far more efficient than most that were made later. This is partly attributable to the addition of new features, such as auto-defrost, that reduced efficiency. Additionally, post World War 2, refrigerator style became more important than efficiency. This was especially true in the 1970s, when side by side models with ice dispensers and water chillers became popular. However, the reduction in efficiency also comes partly from cost cutting (less insulation). Due to the introduction of new energy requirements, refrigerators made today are much more efficient than those made in the 1930s; they consume the same amount of energy while being three times as large.
The efficiency of older refrigerators can be improved by defrosting (if the unit is manual defrost) and cleaning them regularly, replacing old and worn door seals with new ones, adjusting the thermostat to accommodate the actual contents (a refrigerator needn't be colder than to store drinks and non-perishable items) and also replacing insulation, where applicable. Some sites recommend you clean condenser coils every month or so on units with coils on the rear. It has been proved that this does very little for improving efficiency,][ however, the unit should be able to "breathe" with adequate spaces around the front, back, sides and above the unit. If the refrigerator uses a fan to keep the condenser cool, then this must be cleaned, at the very least, yearly.][
Frost-free refrigerators or freezers use electric fans to cool the appropriate compartment. This could be called a "fan forced" refrigerator, whereas manual defrost units rely on colder air lying at the bottom, versus the warm air at the top to achieve adequate cooling. The air is drawn in through an inlet duct and passed through the evaporator where it is cooled, the air is then circulated throughout the cabinet via a series of ducts and vents. Because the air passing the evaporator is supposedly warm and moist, frost begins to form on the evaporator (especially on a freezer's evaporator). In cheaper and/or older models, a defrost cycle is controlled via a mechanical timer. This timer is set to shut off the compressor and fan and energize a heating element located near or around the evaporator for about 15 to 30 minutes at every 6 to 12 hours. This melts any frost or ice build up and allows the refrigerator to work normally once more. It is believed that frost free units have a lower tolerance for frost, due to their air-conditioner like evaporator coils. Therefore, if a door is left open accidentally (especially the freezer), the defrost system may not remove all frost, in this case, the freezer (or refrigerator) must be defrosted.][
If the defrosting system melts all the ice before the timed defrosting period ends, then a small device (called a defrost limiter) acts like a thermostat and shuts off the heating element to prevent too large a temperature fluctuation, it also prevents hot blasts of air when the system starts again, should it finish defrosting early. On some early frost-free models, the defrost limiter also sends a signal to the defrost timer to start the compressor and fan as soon as it shuts off the heating element before the timed defrost cycle ends. When the defrost cycle is completed, the compressor and fan are allowed to cycle back on.][
Frost free refrigerators, and some early frost free refrigerator/freezers that used a cold plate in their refrigerator section instead of airflow from the freezer section generally don't shut off their refrigerator fans during defrosting. This allows consumers to leave food in the main refrigerator compartment uncovered, and also helps keep vegetables moist. This method also helps reduce energy consumption, because the refrigerator is above freeze point and can pass the warmer-than-freezing air through the evaporator or cold plate to aid the defrosting cycle.
Regarding total life-cycle costs, many governments offer incentives to encourage recycling of old refrigerators. One example is the Phoenix refrigerator program launched in Australia. This government incentive picked up old refrigerators, paying their owners for "donating" the refrigerator. The refrigerator was then refurbished, with new door seals, a thorough cleaning and the removal of items, such as the cover that is strapped to the back of many older units. The resulting refrigerators, now over 10% more efficient, were then distributed to low income families.][
The refrigerator allows the modern family to keep food fresh for longer than before. This, along with the modern supermarket, allows most families, without a sizable garden in which to grow vegetables and raise animals, a vastly more varied diet and improved health resulting from improved nutrition.][ Dairy products, meats, fish, poultry and vegetables can be kept refrigerated in the same space within the kitchen (although raw meat should be kept separate from other foodstuffs for reasons of hygiene).
The refrigerator lets people eat more salads, fresh fruits and vegetables, without having to own a garden or an orchard. Exotic foodstuffs from far-off countries that have been imported by means of refrigeration can be enjoyed in the home because of domestic refrigeration.
While storing healthier foods for longer times, more refrigerators and freezers are stocked with processed, quick-cook foods that are less healthy. Studies that correlate frozen foods and obesity have proven that easy access to a wide variety of products such as frozen dairy products, can lead to a general decline in overall health.
Freezers allow people to buy food in bulk and eat it at leisure, and bulk purchases save money. Ice cream, a popular commodity of the 20th century, was previously only obtained by traveling to where the product was made fresh. Consumers had to eat it on the spot. Now it is a common food item. Ice on demand not only adds to the enjoyment of cold drinks, but is useful for first-aid, and for cold packs that can be kept frozen for picnics or in case of emergency.
Some refrigerators are now divided into four zones to store different types of food:
The capacity of a refrigerator is measured in either litres or cubic feet. Typically the volume of a combined refrigerator-freezer is split to 100 litres (3.53 cubic feet) for the freezer and 140 litres (4.94 cubic feet) for the refrigerator, although these values are highly variable.
Temperature settings for refrigerator and freezer compartments are often given arbitrary numbers by manufacturers (for example, 1 through 9, warmest to coldest), but generally 3 to 5 °C (37 to 41 °F) is ideal for the refrigerator compartment and for the freezer. Some refrigerators must be within certain external temperature parameters to run properly. This can be an issue when placing units in an unfinished area, such as a garage. European freezers, and refrigerators with a freezer compartment, have a four star rating system to grade freezers.
Although both the three and four star ratings specify the same storage times and same minimum temperature of , only a four star freezer is intended for freezing fresh food, and may include a "fast freeze" function (runs the compressor continually, down to as low as ) to facilitate this. Three (or fewer) stars are used for frozen food compartments that are only suitable for storing frozen food; introducing fresh food into such a compartment is likely to result in unacceptable temperature rises. This difference in categorisation is shown in the design of the 4-star logo, where the "standard" three stars are displayed in a box using "positive" colours, denoting the same normal operation as a 3-star freezer, and the fourth star showing the additional fresh food/fast freeze function is prefixed to the box in "negative" colours or with other distinct formatting.
Most European refrigerators include a moist cold refrigerator section (which does require (automatic) defrosting at irregular intervals) and a (rarely frost free) freezer section.
Old refrigerators have been adapted to create low cost passive solar water heating systems. Also, many refrigerators have been refurbished for low-income families in eastern Australia via the Phoenix refrigerator program (see energy efficiency)][
In Mexico the Federal Government has created the program Cambia Tu Viejo Por Uno Nuevo — Change Your Old Refrigerator For A New One. The old refrigerators are recycled to recover their components — refrigerant gas, copper, glass, iron, etc.