Menstruation known as a period or monthly, is the regular discharge of blood and mucosal tissue from the inner lining of the uterus through the vagina. The first period begins between twelve and fifteen years of age, a point in time known as menarche. However, periods may start as young as eight years old and still be considered normal; the average age of the first period is later in the developing world, earlier in the developed world. The typical length of time between the first day of one period and the first day of the next is 21 to 45 days in young women, 21 to 31 days in adults. Bleeding lasts around 2 to 7 days. Menstruation stops occurring after menopause, which occurs between 45 and 55 years of age. Periods stop during pregnancy and do not resume during the initial months of breastfeeding. Up to 80% of women report having some symptoms prior to menstruation. Common signs and symptoms include acne, tender breasts, feeling tired and mood changes; these may interfere with normal life, therefore qualifying as premenstrual syndrome, in 20 to 30% of women.
In 3 to 8%, symptoms are severe. A lack of periods, known as amenorrhea, is when periods do not occur by age 15 or have not occurred in 90 days. Other problems with the menstrual cycle include painful periods and abnormal bleeding such as bleeding between periods or heavy bleeding. Menstruation in other animals occur in primates; the menstrual cycle occurs due to the fall of hormones. This cycle results in the thickening of the lining of the uterus, the growth of an egg; the egg is released from an ovary around day fourteen in the cycle. If pregnancy does not occur, the lining is released in; the first menstrual period occurs after the onset of pubertal growth, is called menarche. The average age of menarche is 12 to 15. However, it may start as early as eight; the average age of the first period is later in the developing world, earlier in the developed world. The average age of menarche has changed little in the United States since the 1950s. Menstruation is the most visible phase of the menstrual cycle and its beginning is used as the marker between cycles.
The first day of menstrual bleeding is the date used for the last menstrual period. The typical length of time between the first day of one period and the first day of the next is 21 to 45 days in young women, 21 to 31 days in adults. Perimenopause is when fertility in a female declines, menstruation occurs less in the years leading up to the final menstrual period, when a female stops menstruating and is no longer fertile; the medical definition of menopause is one year without a period and occurs between 45 and 55 in Western countries. During pregnancy and for some time after childbirth, menstruation does not occur; the average length of postpartum amenorrhoea is longer. In most women, various physical changes are brought about by fluctuations in hormone levels during the menstrual cycle; this includes muscle contractions of the uterus that can accompany menstruation. Some may notice water retention, changes in sex drive, breast tenderness, or nausea. Breast swelling and discomfort may be caused by water retention during menstruation.
Such sensations are mild, some females notice few physical changes associated with menstruation. A healthy diet, reduced consumption of salt and alcohol, regular exercise may be effective for women in controlling some symptoms. Severe symptoms that disrupt daily activities and functioning may be diagnosed as premenstrual dysphoric disorder. Symptoms before menstruation are known as premenstrual molimina. Many women experience painful cramps known as dysmenorrhea, during menstruation. Pain results from muscle contractions. Spiral arteries in the secretory endometrium constrict, resulting in ischemia to the secretory endometrium; this allows the uterine lining to slough off. The myometrium contracts spasmodically in order to push the menstrual fluid through the cervix and out of the vagina; the contractions are mediated by a release of prostaglandins. Painful menstrual cramps that result from an excess of prostaglandin release are referred to as primary dysmenorrhea. Primary dysmenorrhea begins within a year or two of menarche with the onset of ovulatory cycles.
Treatments that target the mechanism of pain include non-steroidal anti-inflammatory drugs and hormonal contraceptives. NSAIDs inhibit prostaglandin production. With long-term treatment, hormonal birth control reduces the amount of uterine fluid/tissue expelled from the uterus, thus resulting in shorter, less painful menstruation. These drugs are more effective than treatments that do not target the source of the pain. Risk factors for primary dysmenorrhea include: early age at menarche, long or heavy menstrual periods, a family history of dysmenorrhea. Regular physical activity may limit the severity of uterine cramps. For many women, primary dysmenorrhea subsides in late second generation. Pregnancy has been demonstrated to lessen the severity of dysmenorrhea, when menstruation resumes. However, dysmenorrhea can continue until menopause. 5–15% of women with dysmenorrhea experience symptoms severe enough to interfere with daily activities. Secondary dysmenorrhea is the diagnosis given when menstruation pain is a secondary cause to another disorder.
Celery is a marshland plant in the family Apiaceae, cultivated as a vegetable since antiquity. Celery has a long fibrous stalk tapering into leaves. Depending on location and cultivar, either its stalks, leaves, or hypocotyl are eaten and used in cooking. Celery seed is used as a spice and its extracts have been used in herbal medicine. Celery leaves are pinnate to bipinnate with rhombic leaflets 3–6 cm long and 2–4 cm broad; the flowers are creamy-white, 2–3 mm in diameter, are produced in dense compound umbels. The seeds are broad ovoid to globose, 1.5 -- 2 mm wide. Modern cultivars have been selected for leaf stalks. A celery stalk separates into "strings" which are bundles of angular collenchyma cells exterior to the vascular bundles. Wild celery, Apium graveolens var. graveolens, grows to 1 m tall. It occurs around the globe; the first cultivation is thought to have happened in the Mediterranean region, where the natural habitats were salty and wet, or marshy soils near the coast where celery grew in agropyro-rumicion-plant communities.
North of the alps wild celery is found only in the foothill zone on soils with some salt content. It prefers nutrient rich, muddy soils, it cannot be found in Austria and is rare in Germany. First attested in English in 1664, the word "celery" derives from the French céleri, in turn from Italian seleri, the plural of selero, which comes from Late Latin selinon, the latinisation of the Ancient Greek: σέλινον, translit. Selinon, "celery"; the earliest attested form of the word is the Mycenaean Greek se-ri-no, written in Linear B syllabic script. Celery was described by Carl Linnaeus in Volume One of his Species Plantarum in 1753; the plants are raised from seed, sown either in a hot bed or in the open garden according to the season of the year, after one or two thinnings and transplantings, they are, on attaining a height of 15–20 cm, planted out in deep trenches for convenience of blanching, effected by earthing up to exclude light from the stems. In the past, celery was grown as a vegetable for winter and early spring.
By the 19th century, the season for celery had been extended, to last from the beginning of September to late in April. In North America, commercial production of celery is dominated by the cultivar called'Pascal' celery. Gardeners can grow a range of cultivars, many of which differ from the wild species in having stouter leaf stems, they are ranged under two classes and red. The stalks grow in tight, parallel bunches, are marketed fresh that way, without roots and just a little green leaf remaining; the stalks are eaten raw, or as an ingredient in salads, or as a flavoring in soups and pot roasts. In Europe, another popular variety is celeriac, Apium graveolens var. rapaceum, grown because its hypocotyl forms a large bulb, white on the inside. The bulb can be kept for months in winter and serves as a main ingredient in soup, it can be shredded and used in salads. The leaves are used as seasoning. Leaf celery is a cultivar from East Asia. Leaf celery is most the oldest cultivated form of celery. Leaf celery has characteristically thin skin stalks and a stronger taste and smell compared to other cultivars.
It is sometimes pickled as a side dish. The wild form of celery is known as "smallage", it has a furrowed stalk with wedge-shaped leaves, the whole plant having a coarse, earthy taste, a distinctive smell. The stalks are not eaten, but the leaves may be used in salads, its seeds are those sold as a spice. With cultivation and blanching, the stalks lose their acidic qualities and assume the mild, aromatic taste particular to celery as a salad plant; because wild celery is eaten, yet susceptible to the same diseases as more well-used cultivars, it is removed from fields to help prevent transmission of viruses like celery mosaic virus. Harvesting occurs; the petioles and leaves are harvested. During commercial harvesting, celery is packaged into cartons which contain between 36 and 48 stalks and weigh up to 27 kg. Under optimal conditions, celery can be stored for up to seven weeks between 0 to 2 °C. Inner stalks may continue growing if kept at temperatures above 0 °C. Shelf life can be extended by packaging celery in micro-perforated shrink wrap.
Freshly cut petioles of celery are prone to decay, which can be prevented or reduced through the use of sharp blades during processing, gentle handling, proper sanitation. Celery stalk may be preserved through pickling by first removing the leaves boiling the stalks in water before adding vinegar and vegetable oil. In the past, restaurants used to store celery in a container of water with powdered vegetable preservative, but it was found that the sulfites in the preservative caused allergic reactions in some people. In 1986, the U. S. Food and Drug Administration banned the use of sulfites on fruits and vegetables intended to be eaten ra
Leipzig is the most populous city in the federal state of Saxony, Germany. With a population of 581,980 inhabitants as of 2017, it is Germany's tenth most populous city. Leipzig is located about 160 kilometres southwest of Berlin at the confluence of the White Elster, Pleiße and Parthe rivers at the southern end of the North German Plain. Leipzig has been a trade city since at least the time of the Holy Roman Empire; the city sits at the intersection of the Via Regia and the Via Imperii, two important medieval trade routes. Leipzig was once one of the major European centers of learning and culture in fields such as music and publishing. Leipzig became a major urban center within the German Democratic Republic after the Second World War, but its cultural and economic importance declined. Events in Leipzig in 1989 played a significant role in precipitating the fall of communism in Central and Eastern Europe through demonstrations starting from St. Nicholas Church. Since the reunification of Germany, Leipzig has undergone significant change with the restoration of some historical buildings, the demolition of others, the development of a modern transport infrastructure.
Leipzig today is an economic centre, the most livable city in Germany, according to the GfK marketing research institution and has the second-best future prospects of all cities in Germany, according to HWWI and Berenberg Bank. Leipzig Zoo is one of the most modern zoos in Europe and ranks first in Germany and second in Europe according to Anthony Sheridan. Since the opening of the Leipzig City Tunnel in 2013, Leipzig forms the centrepiece of the S-Bahn Mitteldeutschland public transit system. Leipzig is listed as a Gamma World City, Germany's "Boomtown" and as the European City of the Year 2019. Leipzig has long been a major center for music, both classical as well as modern "dark alternative music" or darkwave genres; the Oper Leipzig is one of the most prominent opera houses in Germany. It was founded in 1693, making it the third oldest opera venue in Europe after La Fenice and the Hamburg State Opera. Leipzig is home to the University of Music and Theatre "Felix Mendelssohn Bartholdy", it was during a stay in this city that Friedrich Schiller wrote his poem "Ode to Joy".
The Leipzig Gewandhaus Orchestra, established in 1743, is one of the oldest symphony orchestras in the world. Johann Sebastian Bach is one among many major composers who lived in Leipzig; the name Leipzig is derived from the Slavic word Lipsk, which means "settlement where the linden trees stand". An older spelling of the name in English is Leipsic; the Latin name Lipsia was used. The name is cognate with Lipetsk in Liepāja in Latvia. In 1937 the Nazi government renamed the city Reichsmessestadt Leipzig. Since 1989 Leipzig has been informally dubbed "Hero City", in recognition of the role that the Monday demonstrations there played in the fall of the East German regime – the name alludes to the honorary title awarded in the former Soviet Union to certain cities that played a key role in the victory of the Allies during the Second World War; the common usage of this nickname for Leipzig up until the present is reflected, for example, in the name of a popular blog for local arts and culture, Heldenstadt.de.
More the city has sometimes been nicknamed the "Boomtown of eastern Germany", "Hypezig" or "The better Berlin" for being celebrated by the media as a hip urban centre for the vital lifestyle and creative scene with many startups. Leipzig was first documented in 1015 in the chronicles of Bishop Thietmar of Merseburg as urbs Libzi and endowed with city and market privileges in 1165 by Otto the Rich. Leipzig Trade Fair, started in the Middle Ages, has become an event of international importance and is the oldest surviving trade fair in the world. There are records of commercial fishing operations on the river Pleiße in Leipzig dating back to 1305, when the Margrave Dietrich the Younger granted the fishing rights to the church and convent of St Thomas. There were a number of monasteries in and around the city, including a Franciscan monastery after which the Barfußgäßchen is named and a monastery of Irish monks near the present day Ranstädter Steinweg; the foundation of the University of Leipzig in 1409 initiated the city's development into a centre of German law and the publishing industry, towards being the location of the Reichsgericht and the German National Library.
During the Thirty Years' War, two battles took place in Breitenfeld, about 8 kilometres outside Leipzig city walls. The first Battle of Breitenfeld took place in 1631 and the second in 1642. Both battles resulted in victories for the Swedish-led side. On 24 December 1701, an oil-fueled street lighting system was introduced; the city employed light guards who had to follow a specific schedule to ensure the punctual lighting of the 700 lanterns. The Leipzig region was the arena of the 1813 Battle of Leipzig between Napoleonic France and an allied coalition of Prussia, Russia and Sweden, it was the largest battle in Europe before the First World War and the coalition victory ended Napoleon's presence in Germany and would lead to his first exile on Elba. The Monument to the Battle of the Nations celebrating the centenary of this event was completed in 1913. In addition to stimulating German nationalism, the war had a major impact in mobilizing a civic spirit in numerous volunteer activities. Many volunteer militi
Jamaica ginger extract, known in the United States by the slang name "Jake," was a late 19th-century patent medicine that provided a convenient way to bypass Prohibition laws, since it contained between 70% and 80% ethanol by weight. The U. S. Treasury Department, which administered the Prohibition laws, recognized Jake's potential as an illicit alcohol source, because of this, it required changes in the solids content of Jake to discourage drinking; the minimum requirement of ginger solids per cubic centimeter of alcohol resulted in a fluid, bitter and difficult to drink. Department of Agriculture inspectors would test shipments of Jake by boiling the solution and weighing the remaining solid residue. In an effort to trick regulators, bootleggers replaced the ginger solids with a small amount of ginger and either castor oil or molasses. A pair of amateur chemists and bootleggers, Harry Gross and Max Reisman, worked to develop an alternative adulterant that would pass the tests, but still be somewhat palatable.
They sought advice from a professor at MIT who did not realize it was meant for internal consumption. They settled on a plasticizer, tri-o-tolyl phosphate, able to pass the Treasury Department's tests but preserved Jake's drinkability. TOCP was thought to be non-toxic; the resulting type of paralysis is now referred to as organophosphate-induced delayed neuropathy, or OPIDN. In 1930, large numbers of Jake users began to lose the use of their feet; some victims could walk, but they had no control over the muscles which would have enabled them to point their toes upward. Therefore, they would raise their feet high with the toes flopping downward, which would touch the pavement first followed by their heels; the toe first, heel second pattern made a distinctive "tap-click" sound as they walked. This peculiar gait became known as the jake walk and those afflicted were said to have jake leg, jake foot, or jake paralysis. Additionally, the calves of the legs would soften and hang down and the muscles between the thumbs and fingers would atrophy.
Within a few months, the TOCP-adulterated Jake was identified as the cause of the paralysis, the contaminated Jake was recovered. But by that time, it was too late for many victims; some did recover partial, use of their limbs. But for most, the loss was permanent; the total number of victims was never determined, but is quoted as between 30,000 and 50,000. Many victims were immigrants to the United States, most were poor, with little political or social influence; the victims received little assistance. Several blues songs on the subject were recorded in the early 1930s, such as "Jake Walk Papa" by Asa Martin, "Jake Leg Blues" by the Mississippi Sheiks, "Alcohol and Jake Blues" by Tommy Johnson, "Jake Jigga Juke" by Iron Mike Norton, "Jake Liquor Blues" by Ishman Bracey. Although this incident became well known cases of organophosphate poisoning occurred in Germany, Italy, and, on a large scale, in Morocco in 1959, where cooking oil adulterated with jet engine lubricant from an American airbase led to paralysis in 10,000 victims, caused an international incident.
In Sara Gruen's 2006 novel Water for Elephants jake paralysis afflicts one character, after drinking contaminated Jamaica Ginger. In the novel The Black Dahlia, the protagonist reveals early on that his mother went blind and fell to her death after drinking jake, leading to his resentment of his father for purchasing it. In the novel Hotel on the Corner of Bitter and Sweet the main character purchases Jamaica Ginger in order to gain access to a jazz club when he was a minor. In Cormac McCarthy's 1979 novel Suttree, minor character Kenneth "Worm" Hazelwood turns down a drink of homemade whiskey, saying that the last time he drank such liquor, it gave him "the jakeleg." In his autobiography On the Move: A Life, Oliver Sacks describes research that he conducted to develop an animal model of jake paralysis. He was able to duplicate the toxic effects of TOCP on myelinated neurons in chickens. In Jamie Ford's novel Hotel on the Corner of Bitter and Sweet the two young characters Henry and Keiko are given a prescription for Jamaican Ginger in the 1942 portion of the story.
They go to the pharmacy, pick up the bottles, return to the Black Elks club. Due to war rationing and systemic oppression at the time, the black jazz club is not allowed to have a liquor license, so the proprietor uses Jamaican Ginger to make bathtub gin. Songs were recorded at the time about its effects. Several have been included on the compilation albums Jake Walk Blues and Jake Leg Blues There is a marked but unsurprising duplication of songs between those albums. In some cases, different artists used the same title for different songs; the songs on one or both of those albums are, in alphabetic order by title: "Alcohol and Jake Blues" – Tommy Johnson "Bay Rum Blues" - David McCarn and Howard Long "Bear Cat Papa Blues" – Gene Autry and Frankie Marvin "Beer Drinkin' Woman" - Black Ace "Got the Jake Leg Too" - Ray Brothers "Jake Bottle Blues" - Lemuel Turner "Jake Head Boogie" - Lightnin' Hopkins "Jake Jigga Juke" - Iron Mike Norton "Jake Leg Blues" - Willie Lofton "Jake Leg Blues" - Mississippi Sheiks with Bo Carter "Ja
For the phenylpropene derivative, see apiole. Apiol known as'liquid apiol' or'green oil of parsley' is the extracted oleoresin of parsley, rather than the distilled oil. Due to its similarity to the term apiole, care should be taken to avoid confusion. Apiol is an irritant and, in high doses, it can cause liver and kidney damage. Cases of death due to attempted abortion using apiol have been reported. Hippocrates wrote about parsley as a herb to cause an abortion. Plants containing apiole were used by women in the Middle Ages to terminate pregnancies, its use was widespread in the US as ergoapiol or apergol, until a toxic adulterated product containing apiol and tri-ortho-cresyl phosphate was introduced on the American market. Now that safer methods of abortion are available, apiol is forgotten
The density, or more the volumetric mass density, of a substance is its mass per unit volume. The symbol most used for density is ρ, although the Latin letter D can be used. Mathematically, density is defined as mass divided by volume: ρ = m V where ρ is the density, m is the mass, V is the volume. In some cases, density is loosely defined as its weight per unit volume, although this is scientifically inaccurate – this quantity is more called specific weight. For a pure substance the density has the same numerical value as its mass concentration. Different materials have different densities, density may be relevant to buoyancy and packaging. Osmium and iridium are the densest known elements at standard conditions for temperature and pressure but certain chemical compounds may be denser. To simplify comparisons of density across different systems of units, it is sometimes replaced by the dimensionless quantity "relative density" or "specific gravity", i.e. the ratio of the density of the material to that of a standard material water.
Thus a relative density less than one means. The density of a material varies with pressure; this variation is small for solids and liquids but much greater for gases. Increasing the pressure on an object decreases the volume of the object and thus increases its density. Increasing the temperature of a substance decreases its density by increasing its volume. In most materials, heating the bottom of a fluid results in convection of the heat from the bottom to the top, due to the decrease in the density of the heated fluid; this causes it to rise relative to more dense unheated material. The reciprocal of the density of a substance is called its specific volume, a term sometimes used in thermodynamics. Density is an intensive property in that increasing the amount of a substance does not increase its density. In a well-known but apocryphal tale, Archimedes was given the task of determining whether King Hiero's goldsmith was embezzling gold during the manufacture of a golden wreath dedicated to the gods and replacing it with another, cheaper alloy.
Archimedes knew that the irregularly shaped wreath could be crushed into a cube whose volume could be calculated and compared with the mass. Baffled, Archimedes is said to have taken an immersion bath and observed from the rise of the water upon entering that he could calculate the volume of the gold wreath through the displacement of the water. Upon this discovery, he leapt from his bath and ran naked through the streets shouting, "Eureka! Eureka!". As a result, the term "eureka" entered common parlance and is used today to indicate a moment of enlightenment; the story first appeared in written form in Vitruvius' books of architecture, two centuries after it took place. Some scholars have doubted the accuracy of this tale, saying among other things that the method would have required precise measurements that would have been difficult to make at the time. From the equation for density, mass density has units of mass divided by volume; as there are many units of mass and volume covering many different magnitudes there are a large number of units for mass density in use.
The SI unit of kilogram per cubic metre and the cgs unit of gram per cubic centimetre are the most used units for density. One g/cm3 is equal to one thousand kg/m3. One cubic centimetre is equal to one millilitre. In industry, other larger or smaller units of mass and or volume are more practical and US customary units may be used. See below for a list of some of the most common units of density. A number of techniques as well as standards exist for the measurement of density of materials; such techniques include the use of a hydrometer, Hydrostatic balance, immersed body method, air comparison pycnometer, oscillating densitometer, as well as pour and tap. However, each individual method or technique measures different types of density, therefore it is necessary to have an understanding of the type of density being measured as well as the type of material in question; the density at all points of a homogeneous object equals its total mass divided by its total volume. The mass is measured with a scale or balance.
To determine the density of a liquid or a gas, a hydrometer, a dasymeter or a Coriolis flow meter may be used, respectively. Hydrostatic weighing uses the displacement of water due to a submerged object to determine the density of the object. If the body is not homogeneous its density varies between different regions of the object. In that case the density around any given location is determined by calculating the density of a small volume around that location. In the limit of an infinitesimal volume the density of an inhomogeneous object at a point becomes: ρ = d m / d V, where d V is an elementary volume at position r; the mass of the body t
An essential oil is a concentrated hydrophobic liquid containing volatile chemical compounds from plants. Essential oils are known as volatile oils, ethereal oils, aetherolea, or as the oil of the plant from which they were extracted, such as oil of clove. An essential oil is "essential" in the sense that it contains the "essence of" the plant's fragrance—the characteristic fragrance of the plant from which it is derived; the term essential used here does not mean indispensable as with the terms essential amino acid or essential fatty acid which are so called since they are nutritionally required by a given living organism. In contrast to fatty oils, essential oils evaporate without leaving a stain or residue. Essential oils are extracted by distillation by using steam. Other processes include expression, solvent extraction, absolute oil extraction, resin tapping, wax embedding, cold pressing, they are used in perfumes, cosmetics and other products, for flavoring food and drink, for adding scents to incense and household cleaning products.
Essential oils are used for aromatherapy, a form of alternative medicine in which healing effects are ascribed to aromatic compounds. Aromatherapy may be useful to induce relaxation, but there is not sufficient evidence that essential oils can treat any condition. Improper use of essential oils may cause harm including allergic reactions and skin irritation, children may be susceptible to the toxic effects of improper use. Essential oils have been used in folk medicine throughout history; the earliest recorded mention of the techniques and methods used to produce essential oils is believed to be that of Ibn al-Baitar, an Al-Andalusian physician and chemist. Rather than refer to essential oils themselves, modern works discuss specific chemical compounds of which the essential oils are composed. For example: methyl salicylate rather than "oil of wintergreen". Interest in essential oils has revived in recent decades with the popularity of aromatherapy, a branch of alternative medicine that uses essential oils and other aromatic compounds.
Oils are volatilized, diluted in a carrier oil and used in massage, diffused in the air by a nebulizer, heated over a candle flame, or burned as incense. Medical applications proposed by those who sell medicinal oils range from skin treatments to remedies for cancer and are based on historical accounts of use of essential oils for these purposes. Claims for the efficacy of medical treatments, treatment of cancers in particular, are now subject to regulation in most countries. Most common essential oils such as lavender, tea tree oil and eucalyptus are distilled. Raw plant material, consisting of the flowers, wood, roots, seeds, or peel, is put into an alembic over water; as the water is heated, the steam passes through the plant material, vaporizing the volatile compounds. The vapors flow through a coil, where they condense back to liquid, collected in the receiving vessel. Most oils are distilled in a single process. One exception is ylang-ylang, purifed through a fractional distillation; the recondensed water is referred to as a hydrosol, herbal distillate, or plant water essence, which may be sold as another fragrant product.
Hydrosols include rose water, lavender water, lemon balm, clary sage, orange blossom water. The use of herbal distillates in cosmetics is increasing. Most citrus peel oils are expressed cold-pressed. Due to the large quantities of oil in citrus peel and low cost to grow and harvest the raw materials, citrus-fruit oils are cheaper than most other essential oils. Lemon or sweet orange oils are obtained as byproducts of the citrus industry. Before the discovery of distillation, all essential oils were extracted by pressing. Most flowers contain too little volatile oil to undergo expression, but their chemical components are too delicate and denatured by the high heat used in steam distillation. Instead, a solvent such as hexane or supercritical carbon dioxide is used to extract the oils. Extracts from hexane and other hydrophobic solvents are called concretes, which are a mixture of essential oil, waxes and other lipophilic plant material. Although fragrant, concretes contain large quantities of non-fragrant waxes and resins.
Another solvent, such as ethyl alcohol, is used to extract the fragrant oil from the concrete. The alcohol solution is chilled to −18 °C for more than 48 hours which causes the waxes and lipids to precipitate out; the precipitates are filtered out and the ethanol is removed from the remaining solution by evaporation, vacuum purge, or both, leaving behind the absolute. Supercritical carbon dioxide is used as a solvent in supercritical fluid extraction; this method can avoid petrochemical residues in the product and the loss of some "top notes" when steam distillation is used. It does not yield an absolute directly; the supercritical carbon dioxide will extract both the waxes and the essential oils that make up the concrete. Subsequent processing with liquid carbon dioxide, achieved in the same extractor by lowering the extraction temperature, will separate the waxes from the essential oils; this lower temperature process prevents the denaturing of compounds. When the extraction is complete, the pressure is reduced to ambient and the carbon dioxide reverts to a gas, leaving no residue.
Florasol is another solvent used to obtain essential oils. It was developed as a refrigerant to replac