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Acid–base reaction

In chemistry, an acid–base reaction is a chemical reaction that occurs between an acid and a base. It can be used to determine pH via titration. Several theoretical frameworks provide alternative conceptions of the reaction mechanisms and their application in solving related problems; these are called the acid–base theories, for example, Brønsted–Lowry acid–base theory.

Their importance becomes apparent in analyzing acid–base reactions for gaseous or liquid species, or when acid or base character may be somewhat less apparent. The first of these concepts was provided by the French chemist Antoine Lavoisier, around 1776.

It is important to think of the acid–base reaction models as theories that complement each other. For example, the current Lewis model has the broadest definition of what an acid and base are, with the Brønsted–Lowry theory being a subset of what acids and bases are, and the Arrhenius theory being the most restrictive.

Historic development
The concept of an acid–base reaction was first proposed in 1754 by Guillaume-François Rouelle, who introduced the word "base" into chemistry to mean a substance which reacts with an acid to give it solid form (as a salt). Bases are mostly bitter in nature.

Lavoisier's oxygen theory of acids
The first scientific concept of acids and bases was provided by Lavoisier in around 1776. Since Lavoisier's knowledge of strong acids was mainly restricted to oxoacids, such as HNO3 (nitric acid) and H2SO4 (sulfuric acid), which tend to contain central atoms in high oxidation states surrounded by oxygen, and since he was not aware of the true composition of the hydrohalic acids (HF, HCl, HBr, and HI), he defined acids in terms of their containing oxygen, which in fact he named from Greek words meaning "acid-former". The Lavoisier definition held for over 30 years, until the 1810 article and subsequent lectures by Sir Humphry Davy in which he proved the lack of oxygen in hydrogen sulfide (H2S), hydrogen telluride (H2Te), and the hydrohalic acids. However, Davy failed to develop a new theory, concluding that "acidity does not depend upon any particular elementary substance, but upon peculiar arrangement of various substances". One notable modification of oxygen theory was provided by Jöns Jacob Berzelius, who stated that acids are oxides of nonmetals while bases are oxides of metals.

Liebig's hydrogen theory of acids
In 1838, Justus von Liebig proposed that an acid is a hydrogen-containing compound whose hydrogen can be replaced by a metal. This redefinition was based on his extensive work on the chemical composition of organic acids, finishing the doctrinal shift from oxygen-based acids to hydrogen-based acids started by Davy. Liebig's definition, while completely empirical, remained in use for almost 50 years until the adoption of the Arrhenius definition.

Arrhenius definition
The first modern definition of acids and bases in molecular terms was devised by Svante Arrhenius. A hydrogen theory of acids, it followed from his 1884 work with Friedrich Wilhelm Ostwald in establishing the presence of ions in aqueous solution and led to Arrhenius receiving the Nobel Prize in Chemistry in 1903.

As defined by Arrhenius:
 * An Arrhenius acid is a substance that ionises in water to form hydrogen ions (H+); that is, an acid increases the concentration of H+ ions in an aqueous solution.

This causes the protonation of water, or the creation of the hydronium (H3O+) ion. Thus, in modern times, the symbol H+ is interpreted as a shorthand for H3O+, because it is now known that a bare proton does not exist as a free species in aqueous solution. This is the species which is measured by pH indicators to measure the acidity or basicity of a solution. The Arrhenius definitions of acidity and alkalinity are restricted to aqueous solutions and are not valid for most non-aqueous solutions, and refer to the concentration of the solvent ions. Under this definition, pure H2SO4 and HCl dissolved in toluene are not acidic, and molten NaOH and solutions of calcium amide in liquid ammonia are not alkaline. This led to the development of the Brønsted–Lowry theory and subsequent Lewis theory to account for these non-aqueous exceptions.
 * An Arrhenius base is a substance that dissociates in water to form hydroxide (OH-) ions; that is, a base increases the concentration of OH- ions in an aqueous solution.

The reaction of an acid with a base is called a neutralization reaction. The products of this reaction are a salt and water.

In this traditional representation an acid–base neutralization reaction is formulated as a double-replacement reaction. For example, the reaction of hydrochloric acid (HCl) with sodium hydroxide (NaOH) solutions produces a solution of sodium chloride (NaCl) and some additional water molecules.

The modifier (aq) in this equation was implied by Arrhenius, rather than included explicitly. It indicates that the substances are dissolved in water. Though all three substances, HCl, NaOH and NaCl are capable of existing as pure compounds, in aqueous solutions they are fully dissociated into the aquated ions H+, Cl-, Na+ and OH-.

Example: Baking powder
Baking powder is used to cause the dough for breads and cakes to "rise" by creating millions of tiny carbon dioxide bubbles. Baking powder is not to be confused with baking soda, which is sodium bicarbonate (NaHCO3). Baking powder is a mixture of baking soda (sodium bicarbonate) and acidic salts. The bubbles are created because, when the baking powder is combined with water, the sodium bicarbonate and acid salts react to produce gaseous carbon dioxide.

Whether commercially or domestically prepared, the principles behind baking powder formulations remain the same. The acid–base reaction can be generically represented as shown:

The real reactions are more complicated because the acids are complicated. For example, starting with sodium bicarbonate and monocalcium phosphate (Ca(H2PO4)2), the reaction produces carbon dioxide by the following stoichiometry:

A typical formulation (by weight) could call for 30% sodium bicarbonate, 5–12% monocalcium phosphate, and 21–26% sodium aluminium sulfate. Alternately, a commercial baking powder might use sodium acid pyrophosphate as one of the two acidic components instead of sodium aluminium sulfate. Another typical acid in such formulations is cream of tartar (KC4H5O6), a derivative of tartaric acid.

Brønsted–Lowry definition
The Brønsted–Lowry definition, formulated in 1923, independently by Johannes Nicolaus Brønsted in Denmark and Martin Lowry in England, is based upon the idea of protonation of bases through the deprotonation of acids – that is, the ability of acids to "donate" hydrogen ions (H+) –  otherwise known as protons –  to bases, which "accept" them.

An acid–base reaction is, thus, the removal of a hydrogen ion from the acid and its addition to the base. The removal of a hydrogen ion from an acid produces its conjugate base, which is the acid with a hydrogen ion removed. The reception of a proton by a base produces its conjugate acid, which is the base with a hydrogen ion added.

Unlike the previous definitions, the Brønsted–Lowry definition does not refer to the formation of salt and solvent, but instead to the formation of conjugate acids and conjugate bases, produced by the transfer of a proton from the acid to the base. In this approach, acids and bases are fundamentally different in behavior from salts, which are seen as electrolytes, subject to the theories of Debye, Onsager, and others. An acid and a base react not to produce a salt and a solvent, but to form a new acid and a new base. The concept of neutralization is thus absent. Brønsted–Lowry acid–base behavior is formally independent of any solvent, making it more all-encompassing than the Arrhenius model. The calculation of pH under the Arrhenius model depended on alkalis (bases) dissolving in water (aqueous solution). The Brønsted–Lowry model expanded what could be pH tested using insoluble and soluble solutions (gas, liquid, solid).

The general formula for acid–base reactions according to the Brønsted–Lowry definition is:

where HA represents the acid, B represents the base, BH+ represents the conjugate acid of B, and A- represents the conjugate base of HA.

For example, a Brønsted–Lowry model for the dissociation of hydrochloric acid (HCl) in aqueous solution would be the following:

The removal of H+ from the HCl produces the chloride ion, Cl-, the conjugate base of the acid. The addition of H+ to the H2O (acting as a base) forms the hydronium ion, H3O+, the conjugate acid of the base.

Water is amphoteric – that is, it can act as both an acid and a base. The Brønsted–Lowry model explains this, showing the dissociation of water into low concentrations of hydronium and hydroxide ions:

This equation is demonstrated in the image below:

Here, one molecule of water acts as an acid, donating an H+ and forming the conjugate base, OH-, and a second molecule of water acts as a base, accepting the H+ ion and forming the conjugate acid, H3O+.

As an example of water acting as an acid, consider an aqueous solution of pyridine, C5H5N.

In this example, a water molecule is split into a hydrogen ion, which is donated to a pyridine molecule, and a hydroxide ion.

In the Brønsted–Lowry model, the solvent does not necessarily have to be water, as is required by the Arrhenius Acid–Base model. For example, consider what happens when acetic acid, CH3COOH, dissolves in liquid ammonia.

An H+ ion is removed from acetic acid, forming its conjugate base, the acetate ion, CH3COO-. The addition of an H+ ion to an ammonia molecule of the solvent creates its conjugate acid, the ammonium ion, NH4+.

The Brønsted–Lowry model calls hydrogen-containing substances (like HCl) acids. Thus, some substances, which many chemists considered to be acids, such as SO3 or BCl3, are excluded from this classification due to lack of hydrogen. Gilbert N. Lewis wrote in 1938, "To restrict the group of acids to those substances that contain hydrogen interferes as seriously with the systematic understanding of chemistry as would the restriction of the term oxidizing agent to substances containing oxygen." Furthermore, KOH and KNH2 are not considered Brønsted bases, but rather salts containing the bases OH2 and.

Lewis definition
The hydrogen requirement of Arrhenius and Brønsted–Lowry was removed by the Lewis definition of acid–base reactions, devised by Gilbert N. Lewis in 1923, in the same year as Brønsted–Lowry, but it was not elaborated by him until 1938. Instead of defining acid–base reactions in terms of protons or other bonded substances, the Lewis definition defines a base (referred to as a Lewis base) to be a compound that can donate an electron pair, and an acid (a Lewis acid) to be a compound that can receive this electron pair.

For example, boron trifluoride, BF3 is a typical Lewis acid. It can accept a pair of electrons as it has a vacancy in its octet. The fluoride ion has a full octet and can donate a pair of electrons. Thus

is a typical Lewis acid, Lewis base reaction. All compounds of group 13 elements with a formula AX3 can behave as Lewis acids. Similarly, compounds of group 15 elements with a formula DY3, such as amines, NR3, and phosphines, PR3, can behave as Lewis bases. Adducts between them have the formula X3A←DY3 with a dative covalent bond, shown symbolically as ←, between the atoms A (acceptor) and D (donor). Compounds of group 16 with a formula DX2 may also act as Lewis bases; in this way, a compound like an ether, R2O, or a thioether, R2S, can act as a Lewis base. The Lewis definition is not limited to these examples. For instance, carbon monoxide acts as a Lewis base when it forms an adduct with boron trifluoride, of formula F3B←CO.

Adducts involving metal ions are referred to as co-ordination compounds; each ligand donates a pair of electrons to the metal ion. The reaction

can be seen as an acid–base reaction in which a stronger base (ammonia) replaces a weaker one (water).

The Lewis and Brønsted–Lowry definitions are consistent with each other since the reaction

is an acid–base reaction in both theories.

Solvent system definition
One of the limitations of the Arrhenius definition is its reliance on water solutions. Edward Curtis Franklin studied the acid–base reactions in liquid ammonia in 1905 and pointed out the similarities to the water-based Arrhenius theory. Albert F.O. Germann, working with liquid phosgene,, formulated the solvent-based theory in 1925, thereby generalizing the Arrhenius definition to cover aprotic solvents.

Germann pointed out that in many solutions, there are ions in equilibrium with the neutral solvent molecules:
 * solvonium ions: a generic name for positive ions. These are also sometimes called solvo-acids; when protonated solvent, they are lyonium ions.
 * solvate ions: a generic name for negative ions. These are also sometimes called solve-bases; when deprotonated solvent, they are lyate ions.

For example, water and ammonia undergo such dissociation into hydronium and hydroxide, and ammonium and amide, respectively:

Some aprotic systems also undergo such dissociation, such as dinitrogen tetroxide into nitrosonium and nitrate, antimony trichloride into dichloroantimonium and tetrachloroantimonate, and phosgene into chlorocarboxonium and chloride:

A solute that causes an increase in the concentration of the solvonium ions and a decrease in the concentration of solvate ions is defined as an acid. A solute that causes an increase in the concentration of the solvate ions and a decrease in the concentration of the solvonium ions is defined as a base.

Thus, in liquid ammonia, KNH2 (supplying NH2-) is a strong base, and NH4NO3 (supplying NH4+) is a strong acid. In liquid sulfur dioxide (SO2), thionyl compounds (supplying SO(2+)) behave as acids, and sulfites (supplying SO3(2-)) behave as bases.

The non-aqueous acid–base reactions in liquid ammonia are similar to the reactions in water:

Nitric acid can be a base in liquid sulfuric acid:

The unique strength of this definition shows in describing the reactions in aprotic solvents; for example, in liquid N2O4:

Because the solvent system definition depends on the solute as well as on the solvent itself, a particular solute can be either an acid or a base depending on the choice of the solvent: HClO4 is a strong acid in water, a weak acid in acetic acid, and a weak base in fluorosulfonic acid; this characteristic of the theory has been seen as both a strength and a weakness, because some substances (such as SO3 and NH3) have been seen to be acidic or basic on their own right. On the other hand, solvent system theory has been criticized as being too general to be useful. Also, it has been thought that there is something intrinsically acidic about hydrogen compounds, a property not shared by non-hydrogenic solvonium salts.

Lux–Flood definition
This acid–base theory was a revival of the oxygen theory of acids and bases proposed by German chemist Hermann Lux in 1939, further improved by Håkon Flood c. 1947 and is still used in modern geochemistry and electrochemistry of molten salts. This definition describes an acid as an oxide ion (O(2-)) acceptor and a base as an oxide ion donor. For example:

This theory is also useful in the systematisation of the reactions of noble gas compounds, especially the xenon oxides, fluorides, and oxofluorides.

Usanovich definition
Mikhail Usanovich developed a general theory that does not restrict acidity to hydrogen-containing compounds, but his approach, published in 1938, was even more general than Lewis theory. Usanovich's theory can be summarized as defining an acid as anything that accepts negative species or donates positive ones, and a base as the reverse. This defined the concept of redox (oxidation-reduction) as a special case of acid–base reactions.

Some examples of Usanovich acid–base reactions include:

HSAB theory
In 1963, Ralph Pearson proposed a qualitative concept known as the Hard and Soft Acids and Bases principle. later made quantitative with help of Robert Parr in 1984. 'Hard' applies to species that are small, have high charge states, and are weakly polarizable. 'Soft' applies to species that are large, have low charge states and are strongly polarizable. Acids and bases interact, and the most stable interactions are hard–hard and soft–soft. This theory has found use in organic and inorganic chemistry.

ECW model
The ECW model created by Russell S. Drago is a quantitative model that describes and predicts the strength of Lewis acid base interactions, $−ΔH$. The model assigned $E$ and $C$ parameters to many Lewis acids and bases. Each acid is characterized by an $E_{A}$ and a $C_{A}$. Each base is likewise characterized by its own $E_{B}$ and $C_{B}$. The $E$ and $C$ parameters refer, respectively, to the electrostatic and covalent contributions to the strength of the bonds that the acid and base will form. The equation is $$-\Delta H = E_{\rm A}E_{\rm B} + C_{\rm A}C_{\rm B} + W$$

The $W$ term represents a constant energy contribution for acid–base reaction such as the cleavage of a dimeric acid or base. The equation predicts reversal of acids and base strengths. The graphical presentations of the equation show that there is no single order of Lewis base strengths or Lewis acid strengths.

Acid–base equilibrium
The reaction of a strong acid with a strong base is essentially a quantitative reaction. For example,

In this reaction both the sodium and chloride ions are spectators as the neutralization reaction,

does not involve them. With weak bases addition of acid is not quantitative because a solution of a weak base is a buffer solution. A solution of a weak acid is also a buffer solution. When a weak acid reacts with a weak base an equilibrium mixture is produced. For example, adenine, written as AH, can react with a hydrogen phosphate ion, HPO4(2-).

The equilibrium constant for this reaction can be derived from the acid dissociation constants of adenine and of the dihydrogen phosphate ion.

The notation [X] signifies "concentration of X". When these two equations are combined by eliminating the hydrogen ion concentration, an expression for the equilibrium constant, $K$ is obtained.

Acid–alkali reaction
An acid–alkali reaction is a special case of an acid–base reaction, where the base used is also an alkali. When an acid reacts with an alkali salt (a metal hydroxide), the product is a metal salt and water. Acid–alkali reactions are also neutralization reactions.

In general, acid–alkali reactions can be simplified to

by omitting spectator ions.

Acids are in general pure substances that contain hydrogen cations (H+) or cause them to be produced in solutions. Hydrochloric acid (HCl) and sulfuric acid (H2SO4) are common examples. In water, these break apart into ions:

The alkali breaks apart in water, yielding dissolved hydroxide ions:

title: Acid–base reaction


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Abu al-Faraj al-Isfahani

Ali ibn al-Husayn al-Iṣfahānī (أبو الفرج الأصفهاني), also known as Abul-Faraj, (full form: Abū al-Faraj ʿAlī ibn al-Ḥusayn ibn Muḥammad ibn Aḥmad ibn al-Ḥaytham al-Umawī al-Iṣfahānī) (897–967CE / 284–356AH) was a writer, historian, genealogist, poet, musicologist and scribe. He was of Arab-Quraysh origin and mainly based in Baghdad. He is best known as the author of Kitab al-Aghani ("The Book of Songs"), which includes information about the earliest attested periods of Arabic music (from the seventh to the ninth centuries) and the lives of poets and musicians from the pre-Islamic period to al-Isfahani's time. Given his contribution to the documentation of the history of Arabic music, al-Isfahani is characterised by George Sawa as "a true prophet of modern ethnomusicology".

Dates
The commonly accepted dates of al-Isfahani's birth and death are 897–898 and 967, based on the dates given by al-Khatib al-Baghdadi which itself based its information on the testimony of al-Isfahani's student, Muhammad ibn Abi al-Fawaris. However, the credibility of these dates is to be treated with caution. No source places his death earlier than 967, but several place it later. These dates are at odds with a reference in the Kitab Adab al-ghuraba ("The Book of the Etiquettes of Strangers"), attributed to al-Isfahani, to his being in the prime of youth (fi ayyam al-shabiba wa-l-siba) in 967. Calculation of the approximate dates of his birth and death through the life spans of his students and his direct informants suggests that he was born before 902 and died after 960.

Biography
Abu al-Faraj al-Isfahani was born in Isfahan, Persia (present-day Iran) but spent his youth and undertook his early studies in Baghdad (present-day Iraq). He was a direct descendant of the last of the Umayyad caliphs, Marwan II, and was thus connected with the Umayyad rulers in al-Andalus, and seems to have kept up a correspondence with them and to have sent them some of his works. He became famous for his knowledge of early Arabian antiquities.

His later life was spent in various parts of the Islamic world, including in Aleppo with its Hamdanid governor Sayf ad-Dawlah (to whom he dedicated the Book of Songs), and in Ray with the Buwayhid vizier Ibn 'Abbad.

Family
The epithet, al-Isfahani, refers to the city, Isfahan, on the Iranian plateau. Instead of indicating al-Isfahani's birthplace, this epithet seems to be common to al-Isfahani's family. Every reference al-Isfahani makes to his paternal relatives includes the attributive, al-Isfahani. According to Ibn Hazm (994–1064), some descendants of the last Umayyad caliph, Marwan b. Muhammad (691–750), al-Isfahani's ancestor, settled in Isfahan. However, it has to be borne in mind that the earliest information available regarding al-Isfahani's family history only dates to the generation of his great-grandfather, Ahmad b. al-Ḥaytham, who settled in Samarra sometime between 835–6 and 847.

Based on al-Isfahani's references in the Kitab al-Aghani (hereafter, the Aghani), Ahmad b. al-Haytham seems to have led a privileged life in Sāmarrāʾ, while his sons were well-connected with the elite of the Abbasid capital at that time. His son, Abd al-Aziz b. Ahmad, was "one of the high ranking scribes in the days of al-Mutawakkil (r. 847–861) (min kibār al-kuttāb fī ayyām al-Mutawakkil)". Another son, Muhammad b. Ahmad (viz. al-Isfahani's grandfather), was associated with Abbasid officials, the vizier Ibn al-Zayyāt (d. 847), the scribe Ibrahim b. al-Abbas al-Ṣūlī (792–857), and the vizier Ubaydallah b. Sulayman (d. 901), along with the Ṭālibid notables, including al-Husayn b. al-Husayn b. Zayd, who was the leader of the Banu Hashim. The close ties with the Abbasid court continued with Muhammad's sons, al-Hasan and al-Husayn (al-Isfahani's father).

In various places in the Aghani, al-Isfahani refers to Yahya b. Muhammad b. Thawaba (from the Al Thawaba) as his grandfather on his mother's side. It is often suggested that the family of Thawaba, being Shi'i, bequeathed their sectarian inclination to al-Isfahani. However, the identification of the Thawaba family as Shi'is is only found in a late source, Yaqut's (1178–1225) work. While many elite families working under the Abbasid caliphate were Shi'i-inclined, indeed allied with Alids or their partisans, there is no evidence that members of the Thawaba family embraced an extreme form of Shi'ism.

In summary, al-Isfahani came from a family well-entrenched in the networks of the Abbasid elite, which included the officials and the Alids. Despite the epithet, al-Isfahani, it does not seem that the Isfahani family had a strong connection with the city of Isfahan. Rather, the family was mainly based in Sāmarrāʾ, from the generation of Ahmad b. al-Ḥaytham, and then Baghdad.

In the seats of the caliphate, a few members of the al-Isfahani family worked as scribes, while maintaining friendship or alliance with other scribes, viziers and notables. Like many of the court elite, al-Isfahani's family maintained an amicable relationship with the offspring of Ali and allied with families, such as the Thawaba family, sharing their veneration of Ali and Alids. However, it is hard to pinpoint such a reverential attitude towards Alids in terms of sectarian alignment, given the scanty information about al-Isfahani's family and the fluidity of sectarian identities at the time.

Education and career
The Isfahani family's extensive network of contacts is reflected in al-Isfahani's sources. Among the direct informants whom al-Isfahani cites in his works, are members of his own family, who were further connected to other notable families, the Al Thawaba, the Banū Munajjim, the Yazīdīs, the Ṣūlīs, the Banū Ḥamdūn, the Ṭāhirids, the Banū al-Marzubān and the Ṭālibids.

Given that al-Isfahani and his family very likely settled in Baghdad around the beginning of the tenth century, he interacted with a considerable number of the inhabitants of or visitors to that city, including: Jaḥẓa (d. 936), al-Khaffāf, Ali b. Sulaymān al-Akhfash (d. 927/8), and Muhammad b. Jarir al-Ṭabari (d. 922). Like other scholars of his time, al-Isfahani travelled in pursuit of knowledge. Although the details are insufficient to establish the dates of his journeys, based on the chains of transmission (asānīd, sing. isnād) al-Isfahani cites consistently and meticulously in every report, it is certain that he transmitted from ʿAbd al-Malik b. Maslama and ʿĀṣim b. Muhammad in Antakya; ʿAbdallāh b. Muhammad b. Ishaq in Ahwaz; and Yahya b. Aḥmad b. al-Jawn in Raqqa. If we accept the attribution of the Kitab Adab al-ghuraba to al-Isfahani, he once visited Baṣra as well as Ḥiṣn Mahdī, Mattūth, and Bājistrā. Yet, none of these cities seems to have left as much of an impact on al-Isfahani as Kūfa and Baghdad did. While al-Isfahani's Baghdadi informants were wide-ranging in their expertise as well as sectarian and theological tendencies, his Kūfan sources can be characterised as either Shi'i or keen on preserving and disseminating memories that favoured Ali and his family. For example, Ibn ʿUqda (d. 944), mentioned in both the Aghānī and the Maqātil, was invariably cited for the reports about the Alids and their merits.

The journey in search for knowledge taken by al-Isfahani may not be particularly outstanding by the standard of his time, but the diversity of his sources' occupations and expertise is impressive. His informants can be assigned into one or more of the following categories: philologists and grammarians; singers and musicians; booksellers and copyists (sahhafun or warraqun, sing. sahhaf or Warraq); friends; tutors (muʾaddibūn, sing. muʾaddib); scribes (kuttāb, sing. kātib); imams or preachers (khuṭabāʾ, sing. khaṭīb); religious scholars (of the ḥadīth, the Qurʾānic recitations and exegeses, or jurisprudence) and judges; poets; and akhbārīs (transmitters of reports of all sorts, including genealogical, historical, and anecdotal reports). The variety of the narrators and their narrations enriched al-Iṣfahānī's literary output, which covers a wide range of topics from amusing tales to the accounts of the Alids' martyrdom. His erudition is best illustrated by Abu Ali al-Muhassin al-Tanukhi's (941–994) comment: "With his encyclopaedic knowledge of music, musicians, poetry, poets, genealogy, history, and other subjects, al-Iṣfahānī established himself as a learned scholar and teacher."

He was also a scribe and this is not surprising, given his families’ scribal connections, but the details of his kātib activities are rather opaque. Although both al-Tanūkhī and al-Baghdādī refer to al-Isfahani with the attribute, kātib, they mention nothing of where he worked or for whom. The details of his occupation as a scribe only came later, with Yaqut, many of whose reports about al-Isfahani prove problematic. For instance, a report from Yaqut claims that al-Isfahani was the scribe of Rukn al-Dawla (d. 976) and mentions his resentment towards Abū al-Faḍl b. al-ʿAmīd (d. 970). However, the very same report was mentioned by Abū Ḥayyān al-Tawḥīdī (active tenth century) in his Akhlāq al-wazīrayn, where the scribe of Rukn al-Dawla is identified as Abū al-Faraj Ḥamd b. Muhammad, not Abū al-Faraj al-Isfahani."Amongst the Shīʿī narrators whom we have seen, none has memorised poems, melodies, reports, traditions (al-āthār), al-aḥādīth al-musnada (narrations with chains of transmission, including the Prophetic ḥadīth), and genealogy by heart like Abū al-Faraj al-Isfahani. Very proficient in these matters, he is also knowledgeable in the military campaigns and the biography of the Prophet (al-maghāzī and al-sīra), lexicography, grammar, legendary tales (al-khurāfāt), and the accomplishments required of courtiers (ālat al-munādama), like falconry (al-jawāriḥ), veterinary science (al-bayṭara), some notions of medicine (nutafan min al-ṭibb), astrology, drinks (al-ashriba), and other things." Thus, it is hard to know with certainty how and where al-Isfahani was engaged in his capacity as a kātib. Nevertheless, al-Isfahani's association with the vizier, Abū Muḥammad al-Muhallabī (903–963), is well-documented. The friendship between the two began before al-Muhallabī's became vizier in 950. The firm relationship between them is supported by al-Isfahani's poetry collected by al-Thaʿālibī (961–1038): half of the fourteen poems are panegyrics dedicated to al-Muhallabī. In addition, al-Isfahani's own work, al-Imāʾ al-shawāʿir (“Enslaved Women Who Composed Poetry”), is dedicated to the vizier, presumably, al-Muhallabī. His no longer surviving Manājīb al-khiṣyān (“The Noble Eunuchs”), which addresses two castrated male singers owned by al-Muhallabī, was composed for him. His magnum opus, the Aghānī, was very likely intended for al-Muhallabī, as well. In return for his literary efforts, according to al-Tanūkhī, al-Isfahani frequently received rewards from the vizier. Furthermore, for the sake of their long-term friendship and out of his respect for al-Isfahani's genius, al-Muhallabī exceptionally tolerated al-Isfahani's uncouth manners and poor personal hygiene. The sources say nothing about al-Isfahani's fate after al-Muhallabī's death. In his last years, according to his student, Muhammad b. Abī al-Fawāris, he suffered from senility (khallaṭa).

Personality, preferences, and beliefs
As a friend, al-Isfahani was unconventional in the sense that he did not seem to have been bothered to observe the social decorum of his time, as noted by a late biographical source: with his uncleanliness and gluttony, he presented a counterexample to elegance (ẓarf), as defined by one of his teachers, Abu al-Ṭayyib al-Washshāʾ (d. 937). His unconformity to the social norms did not hinder him from being part of al-Muhallabī's entourage or participation in the literary assemblies, but, inevitably, it resulted in frictions with other scholars and detraction by his enemies. Although al-Isfahani appeared eccentric to his human associates, he was a caring owner of his cat, named Yaqaq (white): he treated Yaqaq's colic (qulanj) with an enema (al-ḥuqna).

In contrast to his personal habits, al-Isfahani's prose style is lucid, “in clear and simple language, with unusual sincerity and frankness”. Al-Isfahani's capacity as a writer is well illustrated by Abu Deeb, who depicts al-Isfahani as "one of the finest writers of Arabic prose in his time, with a remarkable ability to relate widely different types of aḵbār in a rich, lucid, rhythmic, and precise style, only occasionally exploiting such formal effects as saǰʿ (rhyming prose). He was also a fine poet with an opulent imagination. His poetry displays preoccupations similar to those of other urban poets of his time". His pinpoint documentation of asānīd and meticulous verification of information, provided in all his works, embody a truly scholarly character. Usually, in his treatment of a subject or an event, al-Isfahani lets his sources speak, but, occasionally, he voices his evaluation of poems and songs, as well as their creators. When dealing with conflicting reports, al-Isfahani either leaves his readers to decide or issues his judgement as to the most credible account. Yet, he frankly condemns sources whom he holds to be unreliable, for instance, Ibn Khurdādhbih on musicological information and Ibn al-Kalbī on genealogy. Indeed, al-Isfahani assesses his source material with a critical eye, while striving to present a more balanced view on his biographies, by focusing on their merits instead of elaborating on their flaws.

That said, al-Isfahani's personal preferences and sectarian partisanship are not absent from his works. In terms of music and songs, al-Isfahani favours Ishaq b. Ibrahim al-Mawsili (772–850). In al-Isfahani's view, Ishaq b. Ibrahim was a multi-talented man, who excelled in a number of subjects, but, most importantly, music. Ishaq b. Ibrahim, as a collector of the reports about poets and singers, is an important source in his Aghānī. Besides being a mine of information, Ishaq b. Ibrahim's terminology for the description of the melodic modes is preferred over that of his opponent, Ibrahim ibn al-Mahdi (779–839), and adopted by al-Isfahani in his Aghani. Furthermore, al-Isfahani embarked on the compilation of the Aghānī because he was commissioned by his patron to reconstruct the list of the exquisite songs selected by Ishaq. In other words, the raison d’etre of the Aghānī is partly related to al-Isfahani's idol, Ishaq b. Ibrahim, and its information about singers, songs and performance owes a tremendous amount to him. Al-Isfahani's admiration for scholars or men of letters can be detected from time to time, usually in the passing comments in the chains of transmission. Yet al-Isfahani outspokenly expresses his admiration, in some cases, such as that of Ibn al-Muʿtazz (862–909).

As an Umayyad by ancestry, al-Isfahani's later biographers mention his Shi'i affiliation with surprise. Yet, in the light of the history of the family's connections with the Abbasid elite of Shi'i inclination and the Ṭālibids, and of his learning experience in Kūfa, his Shi'i conviction is understandable. Al-Tusi (995–1067) is the only early source specifying the exact sect to which al-Isfahani belonged in the fluid Shi'i world: he was a Zaydī. Although al-Ṭūsī's view is widely accepted, its veracity is not beyond doubt. Al-Isfahani does not seem to have been informed of the latest Zaydī movements in Yemen and Ṭabaristān during his life, while his association with the Kūfan Zaydī community, which to some degree became less distinguishable from the Sunnīs, is yet to be studied in depth. It is clear, based on examination of how al-Isfahani amended the reports at his disposal, that he honoured Ali, who played a far more prominent role in his works than the first three caliphs, and some of his descendants, including Zaydi Shi'ism's eponym, Zayd ibn Ali (694–740), by presenting them positively, while, in some cases, leaving their enemies’ rectitude in question. In spite of that, al-Isfahani is neither keen to identify the imams in the past, nor discuss the qualities of an imam. As a matter of fact, he hardly uses the word, not even applying it to Zayd b. Ali. Furthermore, he does not unconditionally approve any Alid revolt and seems lukewarm towards the group he refers to as Zaydis. Taken together, al-Isfahani's Shi'i conviction is better characterised as moderate love for Ali without impugning the dignity of the caliphs before him.

Legacy
Al-Isfahani authored a number of works, but only a few survive. Three of them are preserved through quotations: al-Qiyan ("The Singing Girls Enslaved by Men"), al-Diyarat ("The Monasteries"), and Mujarrad al-aghani (“The Abridgement of the Book of Songs”). A fragment of the Mujarrad al-aghani is found in Ibn Abi Uṣaybi'a's ʿUyun al-anba' fi tabaqat al-atibbaʾ, which quotes a poem by the caliph, al-Maʾmūn (r. 813–833), which was arranged as a song by Mutayyam. The first two have been reconstructed and published by al-ʿAtiyya, who collected and collateed the passages from later works that quote from al-Isfahani. The former, al-Qiyān, is a collection of the biographies of the enslaved singing girls. In it, al-Isfahani provided the basic information about the biographical subjects, the men who enslaved them, and their interaction with poets, notables such as caliphs, and their admirers, with illustration of their poetic and/or musical talents. The latter, al-Diyārāt, provides information related to monasteries, with the indication of their geographical locations and, sometimes, history and topographical characteristics. However, it is questionable to what extent the reconstructed editions can represent the original texts, since the passages, which quote al-Isfahani as a source for the given subject and are thus included by the editor, seldom identify the titles of the works.

Four works survive in manuscripts and have been edited and published: Maqātil al-Ṭālibīyīn ("The Ṭālibid Martyrs"), Kitab al-Aghani ("The Book of the Songs"), Adab al-ghuraba ("The Etiquettes of the Strangers"), and al-Ima al-shawair ("The Enslaved Women Who Composed Poetry"). As noted above, al-Isfahani's authorship of the Adab al-ghurabaʾ is disputed. The author, whoever he may have been, mentions in the preface his sufferings from the hardship of time and vicissitude of fate, and the solace which he seeks through the stories of bygone people. Hence, he collects in the Adab al-ghuraba the reports about the experiences of strangers; those away from their homes or their beloved ones. Some of the stories centre on the hardship which strangers, anonymous or not, encountered in their journey or exile, usually shown in the epigrams written on monuments, rocks, or walls. Others relate excursions to the monasteries for drinking.

The al-Imāʾ al-shawāʿir was composed at the order of the vizier al-Muhallabī, al-Isfahani's patron, who demanded the collection of the reports about the enslaved women who composed poetry from the Umayyad to the Abbasid periods. Al-Isfahani confesses that he could not find any noteworthy poetess in the Umayyad period, because the people at that time were not impressed with verses featuring tenderness and softness. Thus, he only records the Abbasid poetesses, with mention of the relevant fine verses or the pleasant tales, and arranges them in chronological order. There are 31 sections, addressing 32 poetesses, most of which are short and usually begin with al-Isfahani's summary of the subject.

The Maqātil al-Ṭālibīyīn is a historical-biographical compilation concerning the descendants of Abu Talib, who died by being killed, poisoned to death in a treacherous way, on the run from the rulers’ persecution, or confined until death. The Maqātil literature was rather common, particularly amongst Shi'is, before al-Isfahani and he used many works of this genre as sources for the Maqātil al-Ṭālibīyīn. Al-Isfahani does not explain the motivation behind this compilation nor mention to whom they were dedicated, but according to the preface of this work, he sets out as a condition to recount the reports about the Ṭālibids who were “praiseworthy in their conduct and rightly guided in their belief (maḥmūd al-ṭarīqa wa-sadīd al-madhhab)”.

Like the al-Imāʾ, the work is structured in chronological order, beginning with the first Ṭālibī martyr, Jaʿfar b. Abī Ṭālib, and ends in the year of its compilation, August 925 (Jumādā I 313). For each biographical entry, al-Isfahani gives the full name, the lineage (sometimes adding the maternal side). Less often, he additionally gives the virtues and personal traits of the subject and other material he thinks noteworthy, for example the prophetic ḥadīth about, or transmitted by, the subject of the biography in question. Then, al-Isfahani gives the account of the death which, more often than not, constitutes the end of the entry. Sometimes poetry for or by the subject is attached. The Maqātil was used as a reliable source of information by many Shi'i and non-Shi'i compilers of the following centuries.

The Kitab al-Aghani, al-Isfahanis best known work, is an immense compilation, including songs provided with musical indications (melodic modes and meters of songs), the biographies of poets and musicians of different periods in addition to historical material. As noted above, al-Isfahani embarks on compiling the Aghani first under the command of a patron, whom he calls ra'is (chief), to reconstruct the list of one hundred fine songs, selected by Ishaq b. Ibrahim. Due to an obscure report in Yaqut's Mu'jam, this raʾīs is often assumed to be Sayf al-Dawla al-Ḥamdānī (r. 945–967), but recent studies suggest that a more plausible candidate for the dedication of the Aghani is the vizier al-Muhallabī.

The Aghani is divided into three parts: first, The Hundred Songs (al-mi'a al-ṣawt  al-mukhtara) and other song collections; second, the songs of the caliphs and of their children and grandchildren (aghani al-khulafa wa-awladihim wa-awlad awladihim); and third, al-Isfahanis selection of songs. The articles in each part are arranged based on different patterns, but it is mostly the song which introduces the articles on biographies or events. The Kitab al-Aghani is not the first book or collection of songs in Arabic, but it can be asserted that it is the most important one, for it "is a unique mine of information not only on hundreds of song texts with their modes and meters, but also on the lives of their poets and composers, and on the social context of music making in early Islam and at the courts of the caliphs in Damascus and Baghdad". Because of al-Isfahani's pedantic documentation of his sources, the Kitab al-Aghani can also be used to reconstruct earlier books of songs or biographical dictionaries on musicians that are otherwise lost.

As for the works that did not survive, based on their contents, as implied by their titles, they can be divided into the following categories:

The genealogical works: Nasab Bani Abd Shams ("The Genealogy of the Banu Abd Shams"), Jamharat al-nasab ("The Compendium of Genealogies"), Nasab Bani Shayban ("The Genealogy of the Banu Shayban"), and Nasab al-Mahaliba ("The Genealogy of the Muhallabids"), this last probably dedicated to his patron, the vizier al-Muhallabi.

The reports about specified or unspecified topics, such as Kitab al-Khammarin wa-l-khammarat ("The Book of Tavern-Keepers, Male and Female"), Akhbar al-tufayliyin ("Reports about Party Crashers"), al-Akhbar wa-l-nawadir ("The Reports and Rare Tales"), and Ayyam al-arab ("The Battle-Days of the Arabs"), which mentions 1700 days of the pre-Islamic tribal battles and was in circulation only in Andalusia.

The reports about music, musicians and singers: the aforementioned Manajib al-khisyan ("The Noble Eunuchs"), Akhbzr Jahza al-Barmaki ("The Reports concerning Jahza al-Barmaki"), al-Mamalik al-shu'ara ("The Slave Poets"), Adab al-samz ("The Etiquettes of Listening to Music"), and Risala fi 'ilal al-nagham ("The Treatise on the Rules of Tones").

There are two works, only mentioned by al-Tusi: Kitab ma nazala min al-Qur'an fi amir al-mu'minīn wa-ahl baytih 'alayhim al-salam ("The Book about the Qur'anic Verses Revealed regarding the Commander of the Faithful and the People of His Family, Peace upon Them") and Kitab fihi kalam Fatima alayha al-salam fi Fadak ("The Book concerning the Statements of Fāṭima, Peace upon Her, regarding Fadak"). Should the attribution of these two works to al-Isfahani be correct, together with the Maqatil al-Talibiyin, they reveal al-Isfahani's Shi'i partisanship.

Works
Al-Isfahani is best known as the author of Kitab al-Aghani ("The Book of Songs"), an encyclopaedia of over 20 volumes and editions. However, he additionally wrote poetry, an anthology of verses on the monasteries of Mesopotamia and Egypt, and a genealogical work. The first printed edition, published in 1868, contained 20 volumes. In 1888 Rudolf Ernst Brünnow published a 21st volume being a collection of biographies not contained in the Bulāq edition, edited from manuscripts in the Royal Library of Munich.
 * Kitāb al-Aġānī (كتاب الأغاني) 'Book of Songs', a collection of Arabic chants rich in information on Arab and Persian poets, singers and other musicians from the 7th to the 10th centuries of major cities such as Mecca, Damascus, Isfahan, Rey, Baghdād and Baṣrah. The Book of Songs contains details of the ancient Arab tribes and courtly life of the Umayyads and provides a complete overview of the Arab civilization from the pre-Islamic Jahiliyya era, up to his own time. Abu ‘l-Faraj employs the classical Arabic genealogical device, or isnad, (chain of transmission), to relate the biographical accounts of the authors and composers. Although originally the poems were put to music, the musical signs are no longer legible. Abu ‘l-Faraj spent in total 50 years creating this work, which remains an important historical source.

 * Maqātil aṭ-Ṭālibīyīn (مقاتل الطالبيين}), Tālibid Fights, a collection of more than 200 biographies of the descendants of Abu Talib ibn Abd al-Muttalib, from the time of Muhammad to the writing of the book in 925/6, who died in an unnatural way. As Abul-Faraj said in the foreword to his work, he included only those Tālibids who rebelled against the government and were killed, slaughtered, executed or poisoned, lived underground, fled or died in captivity. The work is a major source for the Umayyad and Abbāsid Alid uprisings and the main source for the Hashimite meeting that took place after the assassination of the Umayyad Caliph al-Walīd II in the village of al-Abwā' between Mecca and Medina. At this meeting, al-'Abdallah made the Hashimites pledge an oath of allegiance to his son Muhammad al-Nafs al-Zakiyya as the new Mahdi.
 * Kitāb al-Imā'āš-šawā'ir (كتاب الإماء الشواعر) 'The Book of the Poet-slaves', a collection of accounts of poetic slaves of the Abbasid period.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Abu al-Faraj al-Isfahani


text:
Alcobaça, Portugal

Alcobaça is a Portuguese city and municipality in the intermunicipal community Oeste and the region Oeste e Vale do Tejo, in the historical province of Estremadura, and in the Leiria District. The city grew along the valleys of the rivers Alcoa and Baça, from which it derives its name. The municipality population in 2011 was 56,693, in an area of 408.14 km2. The city proper has a population of 15,800 inhabitants.

The city of Alcobaça became notable after the first king of Portugal, Afonso Henriques, decided to build a church to commemorate the Conquest of Santarém from the Moors in 1147. The church later evolved into the Monastery of Alcobaça, one of the most magnificent Gothic monuments in the country. In the church are the tombs of Pedro I of Portugal and his murdered mistress Inês de Castro. Over the centuries this monastery played an important role in shaping Portuguese culture.

A few kilometers to the north of Alcobaça is the Monastery of Batalha, another Gothic building constructed in memory of a different important battle, that of Aljubarrota. To the west of Alcobaça is the fishing village of Nazaré, now a popular resort town. To the south is the city of Caldas da Rainha and the medieval town of Óbidos. To the northeast is the town of Porto de Mós with its rebuilt castle.

History
Alcobaça became notable in the 12th century, when it was chosen as the future site of Portugal's largest church. In March 1147, the young King Dom Afonso Henriques defeated the Moors by capturing the city of Santarém. As a tribute to his victory, he vowed to build a magnificent home for the Order of Cistercians. It took another 76 years before this task was completed. The monarchy continued to carry out further construction and 60 years later King Dinis built the main cloister. The monastery was consecrated in 1262.

The church contains the tombs of Pedro I of Portugal and his murdered mistress Inês de Castro. Pedro had married Constanza, the Infanta (princess) of Castile, but escaped with his mistress Inês and later lived in the city of Coimbra. His father, King Afonso IV, believing that the family of Inês was a threat to his kingdom, had her murdered. Shortly after the death of his father, Pedro declared that he had married Inês in a prior secret ceremony in Bragança, and took a gruesome revenge on the killers and exhumed her body. He presented the embalmed corpse at the court with a crown on her head and demanded that all his courtiers kneel and individually pay homage to her decomposed hand. Today, their ornate tombs face each other so that on Judgment Day his first sight would be of Inês.

During the following centuries, the monks from this monastery had a major influence on the development of Portuguese culture. Notably, in 1269 they were the first to give public lessons to their congregation, and later they produced the first authoritative history on Portugal in a series of books. In 1810, the invading French pillaged the abbey, taking with them most of its most important treasures, including the noteworthy library. The items that remained were later stolen in 1834 during an anti-clerical riot and the banning of religious orders in Portugal.

Climate
Alcobaça has a Mediterranean climate (Köppen:Csb) with warm, dry summers and mild, wet winters.

Parishes
Administratively, the municipality is divided into 13 civil parishes (freguesias):

 * Alcobaça e Vestiaria
 * Alfeizerão
 * Aljubarrota
 * Bárrio
 * Benedita
 * Cela
 * Coz, Alpedriz e Montes
 * Évora de Alcobaça
 * Maiorga
 * Pataias e Martingança
 * São Martinho do Porto
 * Turquel
 * Vimeiro

City information
The main feature of the city is essentially the monastery that proudly presents a long and sombre façade with 18th-century embellishments. This austerity is further emphasized in the cloisters with its apt name of "Cloister of Silence". In contrast within the Abbey is the massive kitchen with a running stream specially diverted to pass through as a supply of fresh water. The open area of the kitchen chimney is large enough to take a whole ox for roasting. The surround to the sacristy doorway is an outstanding example of Manueline decoration. In 1794, Lord Beckford visited the Abbey and commented that he found some 300 monks "living in a very splendid manner"!

Nearby locations
A few kilometers to the north of Alcobaça is another wondrous building constructed in memory of a different important battle, that of Aljubarrota in 1385, when King John I of Portugal defeated the Castilians and ensuring two hundred years of independence from the Castilian invaders. The construction of the Abbey at Batalha commenced in 1388 and was added to by various Portuguese Kings over these next two centuries. To the east of Batalha is the world-famous location of Fátima and a point of pilgrimage for the Roman Catholic religion due to the vision of the Virgin Mary in 1917 by three young children whilst tending their flock. To the west of Alcobaça is the well-known fishing village of Nazaré. Today, the village is now a small town and a popular holiday resort with most of its past and traditions having rapidly evaporated in the course of time. A very successful Portuguese feature film was made in the early 20th century that dramatically captured the primitive and dangerous life of these fishermen. Stoutly Catholic, the inhabitants have retained some of their past as can be still seen in their own particular style of costume. To the south is Caldas da Rainha and the quaint medieval town of Óbidos that is an attraction for any tourists that enjoys a true glimpse of the past. Also to the south is the town of Porto de Mós with its fanciful rebuilt castle. This town borders the Nature Reserve Parque Natural das Serras de Aire e Candeeiros. These 390 square kilometres of limestone-covered landscape is also known for its caverns. The best known being the Grutas de Mira de Aire can be visited and consists of tunnels, caverns with stalactites, stalagmites, lakes, and a music and light finale.

Major events

 * Market days – Every Monday
 * Carnaval de Alcobaça – February/March
 * Cistermúsica – classical music festival – June / July
 * Saint Bernard's fair – August 20
 * Municipal holiday – August 20
 * Marionetas na Cidade – puppetry festival – mid-October
 * Saint Simon's fair – 4th week of October
 * International display of Sweets and Conventual Liqueurs – November

Notable people from Alcobaça

 * Joaquim Ferreira Bogalho (1889–1977) the 20th president of S.L. Benfica
 * Virgínia Vitorino, (Wiki PT) (1895–1967) a teacher, poet and playwright.
 * Joaquim Vieira de Natividade, (Wiki PT) (1899–1968) an agricultural engineer
 * Valdemar José Correia Barbosa Rodrigues, (Wiki PT) (b. 1965) an environmental engineer, ensaist and poet
 * José Aurélio, (Wiki PT) (born 1938) a sculptor, works in stone, wood and bronze
 * João Lourenço (born 1942) a former footballer with 207 club caps
 * Alberto Costa (born 1947) politician, Minister of Justice, 2005-2009.
 * Nuno Gonçalves, a Portuguese musician, founder of The Gift.
 * João Traquina (born 1988) a Portuguese footballer with over 350 club caps
 * João Pedro Silva (born 1989) a Portuguese professional triathlete, competed at the 2012 Summer Olympics
 * The Gift (formed 1994) a Portuguese alternative rock band
 * Loto (formed 2002) an electro-pop-rock-dance music band
 * Spartak! (2006–2008) a musical collective from Alcobaça
 * JÜRA Popular pop artist based in Lisbon

International relations
Alcobaça is twinned with:
 * 🇫🇷 Aubergenville, France
 * 🇵🇱 Bełchatów, Poland
 * Cacuaco, Angola
 * 🇺🇸 Chicopee, United States

title: Alcobaça, Portugal


text:
Amphisbaena

The amphisbaena (,, or , plural: amphisbaenae; ἀμφίσβαινα) is a mythological, ant-eating serpent with a head at each end. The creature is alternatively called the amphisbaina, amphisbene, amphisboena, amphisbona, amphista, amfivena, amphivena, or anphivena (the last two being feminine), and is also known as the "Mother of Ants". Its name comes from the Greek words ', meaning "both ways", and ', meaning "to go".

Mythology
According to Greek mythology, the amphisbaena was spawned from the blood that dripped from the Gorgon Medusa's head as Perseus flew over the Libyan Desert with her head in his hand, after which Cato's army then encountered it along with other serpents on the march. Amphisbaena fed on the corpses left behind. The amphisbaena has been referred to by various poets such as Nicander, John Milton, Alexander Pope, Percy Bysshe Shelley, Alfred Tennyson, Aimé Césaire, A. E. Housman and Allen Mandelbaum; as a mythological and legendary creature, it has been referenced by Lucan, Pliny the Elder, Isidore of Seville, and Thomas Browne, the last of whom debunked its existence ( book three chapter XV).

Appearance

"The amphisbaena has a twin head, that is one at the tail end as well, as though it were not enough for poison to be poured out of one mouth." "The Amphisbaena however is a snake with two heads, one at the top and one in the direction of the tail. When it advances, as need for a forward movement impels it, it leaves one end behind to serve as tail, while the other it uses as a head. Then again if it wants to move backwards, it uses the two heads in exactly the opposite manner from what it did before." "The amphisbaena grows twin heads, one in the proper place, and the other where the tail should be. For this reason the snake glides in a circular shape, as the heads, contrary to what is right, strain from both ends."

These early descriptions of the amphisbaena depict a venomous, dual-headed snakelike creature. However, medieval and later drawings often show it with two or more scaled feet, particularly chicken feet, and feathered wings. Some even depict it as a horned, dragon-like creature with a serpent-headed tail and small, round ears, while others have both "necks" of equal size so that it cannot be determined which is the rear head. Many descriptions of the amphisbaena say its eyes glow like candles or lightning, but the poet Nicander seems to contradict this by describing it as "always dull of eye". He also says: "From either end protrudes a blunt chin; each is far from each other." Nicander's account seems to be referring to what is indeed called the Amphisbaenia, a group of real lizards.

Habitat
The amphisbaena is said to make its home in the desert.

Folk medicine
In ancient times, the supposedly dangerous amphisbaena had many uses in the art of folk medicine and other such remedies. Pliny notes that expecting women wearing a live amphisbaena around their necks would have safe pregnancies; however, if one's goal was to cure ailments such as arthritis or the common cold, one should wear only its skin. By eating the meat of the amphisbaena, one could supposedly attract many lovers of the opposite sex, and slaying one during the full moon could give power to one who is pure of heart and mind. Lumberjacks suffering from cold weather on the job could nail its carcass or skin to a tree to keep warm, while in the process allowing the tree to be felled more easily.

Origins
In The Book of Beasts, T.H. White suggests that the creature derives from sightings of the worm lizards of the same name. These creatures are found in the Mediterranean countries where many of these legends originated.

The Códice Casanatense (c. 1540), a Portuguese book describing the areas the Portuguese had visited, includes an illustration of the flora and fauna of India. One of the animals shown is a two-headed snake (conjoined twin snakes), with one head on each end, much like an amphisbaena. The image is captioned, "two headed snakes of India are harmless". It is possible a sighting of an animal like this was the origin of the amphisbaena.

In media
In Dante's Inferno, the amphisbaena is listed as one of the types of reptiles that torment thieves in the seventh bolgia.

In John Milton's Paradise Lost, after the Fall and the return of Satan to Hell, some of the fallen angelic host are transformed into the amphisbaena, to represent the animal by which the Fall was caused, i.e. a snake.

Amphisbaena appears in some editions of the tabletop roleplaying game Dungeons & Dragons.

Amphisbaena has appeared in several video games as an enemy or boss monster, including La-Mulana and Bravely Second: End Layer. A creature called Amphisbaena appears in the games Castlevania: Symphony of the Night and Portrait of Ruin but bears little resemblance to other renditions of the creature, appearing as an eyeless 4-legged reptile with the upper body of a human woman sprouting from its long tail instead of a double-headed serpent.

In the 1984 animated film Gallavants, an amphisbaena (called a 'Vanterviper' in the film) appears as a minor antagonist. The two heads, a red one named Edil and a blue one called Fice, frequently disagree and argue, and sing a song about their miserable plight.

The amphisbaena is mentioned in The Last Wish, from The Witcher series by Andrzej Sapkowski, while protagonist Geralt of Rivia recalls past events. The amphisbaena was endangering the region of Kovir until the beast was slain by Geralt's hand.

Amphisbaena is referenced in RWBY, an animated web series created by Monty Oum, in the form of an evil creature called Grimm. Of the different Grimm, the amphisbaena appears to be the King Taijitu, a two-headed snake or serpent. The king's name references the taijitu, a symbol or diagram in Chinese philosophy representing Taiji in both its monist and dualist aspects. The Grimm's coloration visually symbolizes the taijitu, with one head and body section black and the opposite side white.

The amphisbaena appears in the Rise of the Teenage Mutant Ninja Turtles episode "Battle Nexus: New York." This version is one of the known champions of the Battle Nexus. Big Mama had Michelangelo and Meat Sweats compete to feed each of its heads in order to satisfy the amphisbaena. They managed to work together to pull it off.

Brandon Sanderson's novel Skyward has a character whose name is Arturo Mendez. His call sign is amphisbaena.

Use as a Proverb
The amphisbaena appears also in the popular saying "to the amphisbaena, Perseus is good" which can have various meanings depending in the connotation in which it is used. However, one main meaning lies in the connection between Perseus and the amphisbaena and its creation. Though created out of the violent death of Medusa by Perseus, it shows that the creation will always see the creator in a positive light.

title: Amphisbaena


text:
Amyl alcohol

Amyl alcohols are alcohols with the formula C5H11OH. Eight are known. A mixture of amyl alcohols (also called amyl alcohol) can be obtained from fusel alcohol. Amyl alcohol is used as a solvent and in esterification, by which is produced amyl acetate and other products. The name amyl alcohol without further specification applies to the normal (straight-chain) form, 1-pentanol.

 * {| class="wikitable sortable"

! Common name !! Structure !! Type !! IUPAC name !! Boiling point (°C)
 * +Amyl alcohol isomers
 * 1-pentanol or normal amyl alcohol
 * [[Image:Pentan-1-ol-2D-skeletal.png|150px]]
 * primary
 * Pentan-1-ol
 * 138.5
 * 2-methyl-1-butanol or active amyl alcohol
 * [[Image:2-Methyl-1-butanol.svg|120px]]
 * primary
 * 2-Methylbutan-1-ol
 * 128.7
 * 3-methyl-1-butanol or isoamyl alcohol or isopentyl alcohol
 * [[Image:Isoamyl alcohol.svg|120px]]
 * primary
 * 3-Methylbutan-1-ol
 * 131.2
 * 2,2-dimethyl-1-propanol or neopentyl alcohol
 * [[Image:Neopentyl-alcohol-2D-skeletal.png|100px]]
 * primary
 * 2,2-Dimethylpropan-1-ol
 * 113.1
 * 2-pentanol or sec-amyl alcohol or methyl (n) propyl carbinol
 * [[Image:Pentan-2-ol-2D-skeletal.png|100px]]
 * secondary
 * Pentan-2-ol
 * 118.8
 * 3-methyl-2-butanol or sec-isoamyl alcohol or methyl isopropyl carbinol
 * [[Image:3-methylbutan-2-ol-2D-skeletal.png|80px]]
 * secondary
 * 3-Methylbutan-2-ol
 * 113.6
 * 3-Pentanol
 * [[Image:Pentan-3-ol-2D-skeletal.png|100px]]
 * secondary
 * Pentan-3-ol
 * 115.3
 * 2-methyl-2-butanol or tert-amyl alcohol
 * [[Image:Tert-pentyl-alcohol-2D-skeletal.png|100px]]
 * tertiary
 * 2-Methylbutan-2-ol
 * 102
 * }
 * 115.3
 * 2-methyl-2-butanol or tert-amyl alcohol
 * [[Image:Tert-pentyl-alcohol-2D-skeletal.png|100px]]
 * tertiary
 * 2-Methylbutan-2-ol
 * 102
 * }
 * }

Three of these alcohols, 2-methyl-1-butanol, 2-pentanol, and 3-methyl-2-butanol (methyl isopropyl carbinol), contain stereocenters, and are therefore chiral and optically active.

The most important amyl alcohol is isoamyl alcohol, the chief one generated by fermentation in the production of alcoholic beverages and a constituent of fusel oil. The other amyl alcohols may be obtained synthetically.

title: Amyl alcohol


text:
Amyl nitrite

Amyl nitrite is a chemical compound with the formula C5H11ONO. A variety of isomers are known, but they all feature an amyl group attached to the nitrite functional group. The alkyl group is unreactive and the chemical and biological properties are mainly due to the nitrite group. Like other alkyl nitrites, amyl nitrite is bioactive in mammals, being a vasodilator, which is the basis of its use as a prescription medicine. As an inhalant, it also has a psychoactive effect, which has led to its recreational use, with its smell being described as that of old socks or dirty feet.

It was first documented in 1844 and came into medical use in 1867.

Uses

 * Amyl nitrite was historically employed medically to treat heart diseases as well as angina.
 * Amyl nitrite was sometimes used as an antidote for cyanide poisoning. It was thought to act as an oxidant, to induce the formation of methemoglobin. Methemoglobin in turn can sequester cyanide as cyanomethemoglobin. However, it has been replaced by hydroxocobalamin which had better efficacy, and the use of amyl nitrite has been found to be ineffective and unscientific
 * Amyl nitrite is used as a cleaning agent and solvent in industrial and household applications. It replaced dichlorodifluoromethane, an industrial chemical universally banned in 1996 due to damage to the ozone layer, as a printed circuit board cleaner. Trace amounts are added to some perfumes.
 * It is also used recreationally as an inhalant drug that induces a brief euphoric state, and when combined with other intoxicant stimulant drugs such as cocaine or MDMA, the euphoric state intensifies and is prolonged. Once some stimulative drugs wear off, a common side effect is a period of depression or anxiety, colloquially called a "come down"; amyl nitrite is sometimes used to combat these negative after-effects. This effect, combined with its dissociative effects, has led to its use as a recreational drug (see  poppers).

Nomenclature
The term "amyl nitrite" encompasses several isomers. In older literature, the common non-systematic name amyl was often used for the pentyl group, where the amyl group is a linear or normal (n) alkyl group, and the resulting amyl nitrite would have the structural formula CH3(CH2)3CH2ONO, also referred to as n-amyl nitrite.

A common form of amyl nitrite is the isomer with the formula (CH3)2CHCH2CH2ONO, which may be more specifically referred to as isoamyl nitrite.

The similarly named amyl nitrate has very different properties. At the same time, isopropyl nitrite has a similar structure and similar uses (also called 'poppers') but with worse side-effects.

Amyl nitrite is sometimes referred to colloquially as banapple gas.

Synthesis and reactions
Alkyl nitrites are prepared by the reaction of alcohols with nitrous acid:

 * ROH +  HONO  →  RONO  +  H2O, where R = alkyl group

The reaction is called esterification. Synthesis of alkyl nitrites is, in general, straightforward and can be accomplished in home laboratories. A common procedure includes the dropwise addition of concentrated sulfuric acid to a cooled mixture of an aqueous sodium nitrite solution and an alcohol. The intermediately-formed stoichiometric mixture of nitrogen dioxide and nitric oxide then converts the alcohol to the alkyl nitrite, which, due to its low density, will form an upper layer that can be easily decanted from the reaction mixture.

Isoamyl nitrite decomposes in the presence of base to give nitrite salts and the isoamyl alcohol:
 * C5H11ONO +  NaOH  → C5H11OH  +  NaNO2

Amyl nitrite, like other alkyl nitrites, reacts with carbanions to give oximes.

Amyl nitrites are also useful as reagents in a modification of the Sandmeyer reaction. The reaction of the alkyl nitrite with an aromatic amine in a halogenated solvent produces a radical aromatic species, this then frees a halogen atom from the solvent. For the synthesis of aryl iodides diiodomethane is used, whereas bromoform is the solvent of choice for the synthesis of aryl bromides.

Physiological effects

Amyl nitrite, in common with other alkyl nitrites, is a potent vasodilator; it expands blood vessels, resulting in lowering of the blood pressure. Amyl nitrite may be used during cardiovascular stress testing in patients with suspected hypertrophic cardiomyopathy to cause vasodilation and thereby reduce afterload and provoke obstruction of blood flow towards the aorta from the ventricle by increasing the pressure gradient, thereby causing left ventricular outflow obstruction. Alkyl nitrites are a source of nitric oxide, which signals for relaxation of the involuntary muscles. Physical effects include decrease in blood pressure, headache, flushing of the face, increased heart rate, dizziness, and relaxation of involuntary muscles, especially the blood vessel walls and the internal and external anal sphincter. There are no withdrawal symptoms. Overdose symptoms include nausea, vomiting, hypotension, hypoventilation, shortness of breath, and fainting. The effects set in very quickly, typically within a few seconds and disappear within a few minutes. Amyl nitrite may also intensify the experience of synesthesia. Amyl nitrite, when given as a medication for patients with angina, can also be administered as an ampule. The ampule is put in a gauze pad and then inhaled by the patient during an angina attack and repeated every fifteen minutes. However, oral dosing of amyl nitrite is ineffective due to poor absorption and extensive hepatic metabolism. Amyl nitrite has been widely replaced by nitroglycerin for the treatment of acute angina.

Toxicity
Although there are case reports of life-threatening toxicity involving unusually large amounts, typical inhaled doses of amyl nitrite are considered relatively safe. However, liquid amyl nitrite is highly toxic when ingested because of the unsafely high concentration it causes in blood. Regardless of the form or route of administration, acute toxicity principally results when the nitrite oxidizes a significant proportion of hemoglobin in the blood without oxygen, forming methemoglobin, which cannot carry oxygen. Severe poisoning cases will progress to methemoglobinemia, characterized by a blue-brown discoloration under the skin which could be mistaken for cyanosis. Treatment with oxygen and intravenous methylene blue frustrates visual confirmation further as methylene blue itself is, as its name suggests, a blue dye; the patient's changes in different shades of blue notwithstanding, it is an effective antidote by way of catalyzing the production of the enzyme responsible for reducing the methemoglobin in the blood back to hemoglobin.

The discoloration does mean that regular near-infrared–based pulse oximetry becomes useless. More fundamentally, blood gas analysis on the whole has limited effectiveness, as the increased methemoglobin level increases the oxygen binding affinity of regular hemoglobin. Therefore, the measurement of actual ratios and levels of methemoglobin and hemoglobin must accompany any blood gas partial pressure sample in these cases.

In popular culture
The Columbo episode titled "Troubled Waters" (1974–1975) features amyl nitrite inhaled by the antagonist Hayden Danziger – played by Robert Vaughn – to help him feign a heart attack for his alibi. However, the episode consistently refers to the substance incorrectly as amyl nitrate.

The 1978 Derek Jarman film Jubilee features a character named Amyl Nitrate (a misspelled reference to amyl nitrite).

The punk band Amyl and the Sniffers reference recreational use of amyl nitrite in their name.

title: Amyl nitrite


text:
Autumn

Autumn, also known as fall in North American English, is one of the four temperate seasons on Earth. Outside the tropics, autumn marks the transition from summer to winter, in September (Northern Hemisphere) or March (Southern Hemisphere). Autumn is the season when the duration of daylight becomes noticeably shorter and the temperature cools considerably. Day length decreases and night length increases as the season progresses until the winter solstice in December (Northern Hemisphere) and June (Southern Hemisphere). One of its main features in temperate climates is the striking change in colour for the leaves of deciduous trees as they prepare to shed.

Date definitions
Some cultures regard the autumnal equinox as "mid-autumn", while others with a longer temperature lag treat the equinox as the start of autumn. In the English-speaking world of high latitude countries, autumn traditionally began with Lammas Day and ended around Hallowe'en, the approximate mid-points between midsummer, the autumnal equinox, and midwinter. Meteorologists (and Australia and most of the temperate countries in the southern hemisphere)  use a definition based on Gregorian calendar months, with autumn being September, October, and November in the northern hemisphere, and March, April, and May in the southern hemisphere.

In the higher latitude countries in the Northern Hemisphere, autumn traditionally starts with the September equinox (21 to 24 September) and ends with the winter solstice (21 or 22 December). Popular culture in the United States associates Labor Day, the first Monday in September, as the end of summer and the start of autumn; certain summer traditions, such as wearing white, are discouraged after that date. As daytime and nighttime temperatures decrease, trees change colour and then shed their leaves. Persians celebrate the beginning of the autumn on Mehregan.

Under the traditional East Asian solar term system, autumn starts on or around 8 August and ends on or about 7 November. In Ireland, the autumn months according to the national meteorological service, Met Éireann, are September, October, and November. However, according to the Irish Calendar, which is based on ancient Gaelic traditions, autumn lasts throughout the months of August, September, and October, or possibly a few days later, depending on tradition. In the Irish language, September is known as Meán Fómhair ("middle of autumn") and October as Deireadh Fómhair ("end of autumn"). Late Roman Republic scholar Marcus Terentius Varro defined autumn as lasting from the third day before the Ides of Sextilis (August 11) to the fifth day before the Ides of November (November 9).

Etymology
The word autumn is derived from Latin autumnus, archaic auctumnus, possibly from the ancient Etruscan root autu- and has within it connotations of the passing of the year. Alternative etymologies include Proto-Indo-European ("cold") or  ("dry").

After the Greek era, the word continued to be used as the Old French word autompne (automne in modern French) or autumpne in Middle English, and was later normalised to the original Latin. In the Medieval period, there are rare examples of its use as early as the 12th century, but by the 16th century, it was in common use.

Before the 16th century, harvest was the term usually used to refer to the season, as it is common in other West Germanic languages to this day (cf. Dutch herfst, German Herbst, and Scots hairst). However, as more people gradually moved from working the land to living in towns, the word harvest lost its reference to the time of year and came to refer only to the actual activity of reaping, and autumn, as well as fall, began to replace it as a reference to the season.

The alternative word fall for the season traces its origins to old Germanic languages. The exact derivation is unclear, with the Old English fiæll or feallan and the Old Norse fall all being possible candidates. However, these words all have the meaning "to fall from a height" and are clearly derived either from a common root or from each other. The term came to denote the season in 16th-century England, a contraction of Middle English expressions like "fall of the leaf" and "fall of the year". Compare the origin of spring from "spring of the leaf" and "spring of the year".

During the 17th century, Englishmen began emigrating to the new North American colonies, and the settlers took the English language with them. While the term fall gradually became nearly obsolete in Britain, it became the more common term in North America.

The name backend, a once common name for the season in Northern England, has today been largely replaced by the name autumn.

Harvest
Association with the transition from warm to cold weather, and its related status as the season of the primary harvest, has dominated its themes and popular images. In Western cultures, personifications of autumn are usually pretty, well-fed females adorned with fruits, vegetables and grains that ripen at this time. Many cultures feature autumnal harvest festivals, often the most important on their calendars.

Still-extant echoes of these celebrations are found in the autumn Thanksgiving holiday of the United States and Canada, and the Jewish Sukkot holiday with its roots as a full-moon harvest festival of "tabernacles" (living in outdoor huts around the time of harvest). There are also the many festivals celebrated by indigenous peoples of the Americas tied to the harvest of ripe foods gathered in the wild, the Chinese Mid-Autumn or Moon festival, and many others. The predominant mood of these autumnal celebrations is a gladness for the fruits of the earth mixed with a certain melancholy linked to the imminent arrival of harsh weather.

This view is presented in English poet John Keats' poem To Autumn, where he describes the season as a time of bounteous fecundity, a time of "mellow fruitfulness".

In North America, while most foods are harvested during the autumn, foods usually associated with the season include pumpkins (which are integral parts of both Thanksgiving and Halloween) and apples, which are used to make the seasonal beverage apple cider.

Melancholia
Autumn, especially in poetry, has often been associated with melancholia. The possibilities and opportunities of summer are gone, and the chill of winter is on the horizon. Skies turn grey, the amount of usable daylight drops rapidly, and many people turn inward, both physically and mentally. It has been referred to as an unhealthy season.

Similar examples may be found in Irish poet W.B. Yeats' poem The Wild Swans at Coole where the maturing season that the poet observes symbolically represents his own ageing self. Like the natural world that he observes, he too has reached his prime and now must look forward to the inevitability of old age and death. French poet Paul Verlaine's "Chanson d'automne" ("Autumn Song") is likewise characterised by strong, painful feelings of sorrow. Keats' To Autumn, written in September 1819, echoes this sense of melancholic reflection but also emphasises the lush abundance of the season. The song "Autumn Leaves", based on the French song "Les Feuilles mortes", uses the melancholic atmosphere of the season and the end of summer as a metaphor for the mood of being separated from a loved one.

Halloween
Autumn is associated with Halloween (influenced by Samhain, a Celtic autumn festival), and with it a widespread marketing campaign that promotes it. The Celtic people also used this time to celebrate the harvest with a time of feasting. At the same time though, it was a celebration of death as well. Crops were harvested, livestock were butchered, and Winter was coming.

Halloween, 31 October, is in autumn in the northern hemisphere. Television, film, book, costume, home decoration, and confectionery businesses use this time of year to promote products closely associated with such a holiday, with promotions going from late August or early September to 31 October, since their themes rapidly lose strength once the holiday ends, and advertising starts concentrating on Christmas.

Other associations
In some parts of the northern hemisphere, autumn has a strong association with the end of summer holiday and the start of a new school year, particularly for children in primary and secondary education. "Back to School" advertising and preparations usually occurs in the weeks leading to the beginning of autumn.

Thanksgiving Day is a national holiday celebrated in Canada, in the United States, in some of the Caribbean islands and in Liberia. Thanksgiving is celebrated on the second Monday of October in Canada, on the fourth Thursday of November in the United States (where it is commonly regarded as the start of the Christmas and holiday season), and around the same part of the year in other places. Similarly named festival holidays occur in Germany and Japan.

Television stations and networks, particularly in North America, traditionally begin their regular seasons in their autumn, with new series and new episodes of existing series debuting mostly during late September or early October (series that debut outside the autumn season are usually known as mid-season replacements). A sweeps period takes place in November to measure Nielsen Ratings.

American football is played almost exclusively in the autumn months; at the high school level, seasons run from late August through early November, with some playoff games and holiday rivalry contests being played as late as Thanksgiving. In many American states, the championship games take place in early December. College football's regular season runs from September through November, while the main professional circuit, the National Football League, plays from September through to early January.

Summer sports, such as association football (in Northern America, East Asia, Argentina, and South Africa), Canadian football, stock car racing, tennis, golf, cricket, and professional baseball, wrap up their seasons in early to late autumn; Major League Baseball's championship World Series is popularly known as the "Fall Classic". (Amateur baseball is usually finished by August.) Likewise, professional winter sports, such as ice hockey and basketball, and most leagues of association football in Europe, are in the early stages of their seasons during autumn; American college basketball and college ice hockey play teams outside their athletic conferences during the late autumn before their in-conference schedules begin in winter.

The Christian religious holidays of All Saints' Day and All Souls' Day are observed in autumn in the Northern hemisphere. Easter falls in autumn in the southern hemisphere.

The secular celebration of International Workers' Day also falls in autumn in the southern hemisphere.

Since 1997, Autumn has been one of the top 100 names for girls in the United States.

In Indian mythology, autumn is considered to be the preferred season for the goddess of learning Saraswati, who is also known by the name of "goddess of autumn" (Sharada).

In Asian mysticism, Autumn is associated with the element of metal, and subsequently with the colour white, the White Tiger of the West, and death and mourning.

Tourism
Although colour change in leaves occurs wherever deciduous trees are found, coloured autumn foliage is noted in various regions of the world: most of North America, Eastern Asia (including China, Korea, and Japan), Europe, southeast, south, and part of the midwest of Brazil, the forest of Patagonia, eastern Australia and New Zealand's South Island.

Eastern Canada and New England are famous for their autumnal foliage, and this attracts major tourism (worth billions of US dollars) for the regions.

title: Autumn