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Humus

In classical soil science, humus is the dark organic matter in soil that is formed by the decomposition of plant and animal matter. It is a kind of soil organic matter. It is rich in nutrients and retains moisture in the soil. Humus is the Latin word for "earth" or "ground".

In agriculture, "humus" sometimes also is used to describe mature or natural compost extracted from a woodland or other spontaneous source for use as a soil conditioner. It is also used to describe a topsoil horizon that contains organic matter (humus type, humus form, or humus profile ).

Humus has many nutrients that improve the health of soil, nitrogen being the most important. The ratio of carbon to nitrogen (C:N) of humus commonly ranges between 8:1 and 15:1 with the median being about 12:1. It also significantly improves (decrease) the bulk density of soil. Humus is amorphous and lacks the cellular structure characteristic of organisms.

A similar material, also called humus and often used as fertilizer after composting and if not judged contaminated by pathogens, toxic heavy metals, and persistent organic pollutants according to standard tolerance levels, is the solid residue of secondary wastewater treatment, also called sewage sludge treatment.

Description
The primary materials needed for the process of humification are plant detritus and dead animals and microbes, excreta of all soil-dwelling organisms, and also black carbon resulting from past fires. The composition of humus varies with that of primary (plant) materials and secondary microbial and animal products. The decomposition rate of the different compounds will affect the composition of the humus.

It is difficult to define humus precisely because it is a very complex substance which is not fully understood. Humus is different from decomposing soil organic matter. The latter looks rough and has visible remains of the original plant or animal matter. Fully humified humus, on the contrary, has a uniformly dark, spongy, and jelly-like appearance, and is amorphous; it may gradually decay over several years or persist for millennia. It has no determinate shape, structure, or quality. However, when examined under a microscope, humus may reveal tiny plant, animal, or microbial remains that have been mechanically, but not chemically, degraded. This suggests an ambiguous boundary between humus and soil organic matter, leading some authors to contest the use of the term humus and derived names such as humic substances or humification. However, humus can be considered as having distinct properties, justifying its maintenance as a specific term.

There is little data available on the composition of forest humus because it is a complex mixture that is challenging for researchers to analyze. Researchers in the 1940s and 1960s tried using chemical separation to analyze plant and humic compounds in forest soil, but this proved impossible. Further research has been done in more recent years, though it remains an active field of study.

Humification
Microorganisms decompose a large portion of the soil organic matter into inorganic minerals that the roots of plants can absorb as nutrients. This process is termed "mineralization". In this process, nitrogen (nitrogen cycle) and the other nutrients (nutrient cycle) in the decomposed organic matter are recycled. Depending on the conditions in which the decomposition occurs, a fraction of the organic matter does not mineralize and instead is transformed by a process called "humification". Prior to modern analytical methods, early evidence led scientists to believe that humification resulted in concatenations of organic polymer resistant to the action of microorganisms, however recent research has demonstrated that microorganisms are capable of digesting humus.

Humification can occur naturally in soil or artificially in the production of compost. Organic matter is humified by a combination of saprotrophic fungi, bacteria, microbes and animals such as earthworms, nematodes, protozoa, and arthropods. Plant remains, including those that animals digested and excreted, contain organic compounds: sugars, starches, proteins, carbohydrates, lignins, waxes, resins, and organic acids. Decay in the soil begins with the decomposition of sugars and starches from carbohydrates, which decompose easily as detritivores initially invade the dead plant organs, while the remaining cellulose and lignin decompose more slowly. Simple proteins, organic acids, starches, and sugars decompose rapidly, while crude proteins, fats, waxes, and resins remain relatively unchanged for longer periods of time.

Lignin, which is quickly transformed by white-rot fungi, is one of the primary precursors of humus, together with by-products of microbial and animal activity. The humus produced by humification is thus a mixture of compounds and complex biological chemicals of plant, animal, or microbial origin that has many functions and benefits in soil. Some judge earthworm humus (vermicompost) to be the optimal organic manure.

Stability
Much of the humus in most soils has persisted for more than 100 years, rather than having been decomposed into CO2, and can be regarded as stable; this organic matter has been protected from decomposition by microbial or enzyme action because it is hidden (occluded) inside small aggregates of soil particles, or tightly sorbed or complexed to clays. Most humus that is not protected in this way is decomposed within 10 years and can be regarded as less stable or more labile.

Stable humus contributes few plant-available nutrients in soil, but it helps maintain its physical structure. A very stable form of humus is formed from the slow oxidation (redox) of soil carbon after the incorporation of finely powdered charcoal into the topsoil. This process is speculated to have been important in the formation of the unusually fertile Amazonian terra preta do Indio. However, recent work suggests that complex soil organic molecules may be much less stable than previously thought: “the available evidence does not support the formation of large-molecular-size and persistent ‘humic substances’ in soils. Instead, soil organic matter is a continuum of progressively decomposing organic compounds.″

Horizons
Humus has a characteristic black or dark brown color and is organic due to an accumulation of organic carbon. Soil scientists use the capital letters O, A, B, C, and E to identify the master horizons, and lowercase letters for distinctions of these horizons. Most soils have three major horizons: the surface horizon (A), the subsoil (B), and the substratum (C). Some soils have an organic horizon (O) on the surface, but this horizon can also be buried. The master horizon (E) is used for subsurface horizons that have significantly lost minerals (eluviation). Bedrock, which is not soil, uses the letter R.

Benefits of soil organic matter and humus
The importance of chemically stable humus is thought by some to be the fertility it provides to soils in both a physical and chemical sense, though some agricultural experts put a greater focus on other features of it, such as its ability to suppress disease. It helps the soil retain moisture by increasing microporosity and encourages the formation of good soil structure. The incorporation of oxygen into large organic molecular assemblages generates many active, negatively charged sites that bind to positively charged ions (cations) of plant nutrients, making them more available to the plant by way of ion exchange. Humus allows soil organisms to feed and reproduce and is often described as the "life-force" of the soil.

 * The process that converts soil organic matter into humus feeds the population of microorganisms and other creatures in the soil, and thus maintains high and healthy levels of soil life.
 * The rate at which soil organic matter is converted into humus promotes (when fast) or limits (when slow) the coexistence of plants, animals, and microorganisms in the soil.
 * Effective humus and stable humus are additional sources of nutrients for microbes: the former provides a readily available supply, and the latter acts as a long term storage reservoir.
 * Decomposition of dead plant material causes complex organic compounds to be slowly oxidized (lignin-like humus) or to decompose into simpler forms (sugars and amino sugars, and aliphatic and phenolic organic acids), which are further transformed into microbial biomass (microbial humus) or reorganized and further oxidized into humic assemblages (fulvic acids and humic acids), which bind to clay minerals and metal hydroxides. The ability of plants to absorb humic substances with their roots and metabolize them has been long debated. There is now a consensus that humus functions hormonally rather than simply nutritionally in plant physiology.
 * Humus is a colloidal substance and increases the cation-exchange capacity of soil, hence its ability to store nutrients by chelation. While these nutrient cations are available to plants, they are held in the soil and prevented from being leached by rain or irrigation.
 * Humus can hold the equivalent of 80–90% of its weight in moisture and therefore increases the soil's capacity to withstand drought.
 * The biochemical structure of humus enables it to moderate, i.e. buffer, excessive acidic or alkaline soil conditions.
 * During humification, microbes secrete sticky, gum-like mucilages; these contribute to the crumby structure (tilth) of the soil by adhering particles together and allowing greater aeration of the soil. Toxic substances such as heavy metals and excess nutrients can be chelated, i.e., bound to the organic molecules of humus, and so prevented from leaching away.
 * The dark, usually brown or black, color of humus helps to warm cold soils in spring.
 * Humus can contribute to climate change mitigation through its carbon sequestration potential. Artificial humic acid and artificial fulvic acid synthesized from agricultural litter can increase the content of dissolved organic matter and total organic carbon in soil.

title: Humus


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Hydrogen bond

In chemistry, a hydrogen bond (or H-bond) is primarily an electrostatic force of attraction between a hydrogen (H) atom which is covalently bonded to a more electronegative "donor" atom or group (Dn), and another electronegative atom bearing a lone pair of electrons—the hydrogen bond acceptor (Ac). Such an interacting system is generally denoted Dn\sH***Ac, where the solid line denotes a polar covalent bond, and the dotted or dashed line indicates the hydrogen bond. The most frequent donor and acceptor atoms are the period 2 elements nitrogen (N), oxygen (O), and fluorine (F).

Hydrogen bonds can be intermolecular (occurring between separate molecules) or intramolecular (occurring among parts of the same molecule). The energy of a hydrogen bond depends on the geometry, the environment, and the nature of the specific donor and acceptor atoms and can vary between 1 and 40 kcal/mol. This makes them somewhat stronger than a van der Waals interaction, and weaker than fully covalent or ionic bonds. This type of bond can occur in inorganic molecules such as water and in organic molecules like DNA and proteins. Hydrogen bonds are responsible for holding materials such as paper and felted wool together, and for causing separate sheets of paper to stick together after becoming wet and subsequently drying.

The hydrogen bond is also responsible for many of the physical and chemical properties of compounds of N, O, and F that seem unusual compared with other similar structures. In particular, intermolecular hydrogen bonding is responsible for the high boiling point of water (100 °C) compared to the other group-16 hydrides that have much weaker hydrogen bonds. Intramolecular hydrogen bonding is partly responsible for the secondary and tertiary structures of proteins and nucleic acids.

Definitions and general characteristics
In a hydrogen bond, the electronegative atom not covalently attached to the hydrogen is named the proton acceptor, whereas the one covalently bound to the hydrogen is named the proton donor. This nomenclature is recommended by the IUPAC. The hydrogen of the donor is protic and therefore can act as a Lewis acid and the acceptor is the Lewis base. Hydrogen bonds are represented as H***Y system, where the dots represent the hydrogen bond. Liquids that display hydrogen bonding (such as water) are called associated liquids.

Hydrogen bonds arise from a combination of electrostatics (multipole-multipole and multipole-induced multipole interactions), covalency (charge transfer by orbital overlap), and dispersion (London forces).

In weaker hydrogen bonds, hydrogen atoms tend to bond to elements such as sulfur (S) or chlorine (Cl); even carbon (C) can serve as a donor, particularly when the carbon or one of its neighbors is electronegative (e.g., in chloroform, aldehydes and terminal acetylenes). Gradually, it was recognized that there are many examples of weaker hydrogen bonding involving donor other than N, O, or F and/or acceptor Ac with electronegativity approaching that of hydrogen (rather than being much more electronegative). Although weak (≈1 kcal/mol), "non-traditional" hydrogen bonding interactions are ubiquitous and influence structures of many kinds of materials.

The definition of hydrogen bonding has gradually broadened over time to include these weaker attractive interactions. In 2011, an IUPAC Task Group recommended a modern evidence-based definition of hydrogen bonding, which was published in the IUPAC journal Pure and Applied Chemistry. This definition specifies: "The hydrogen bond is an attractive interaction between a hydrogen atom from a molecule or a molecular fragment X\sH in which X is more electronegative than H, and an atom or a group of atoms in the same or another molecule, in which there is evidence of bond formation."

Bond strength
Hydrogen bonds can vary in strength from weak (1–2 kJ/mol) to strong (161.5 kJ/mol in the bifluoride ion, HF2-). Typical enthalpies in vapor include: The strength of intermolecular hydrogen bonds is most often evaluated by measurements of equilibria between molecules containing donor and/or acceptor units, most often in solution. The strength of intramolecular hydrogen bonds can be studied with equilibria between conformers with and without hydrogen bonds. The most important method for the identification of hydrogen bonds also in complicated molecules is crystallography, sometimes also NMR-spectroscopy. Structural details, in particular distances between donor and acceptor which are smaller than the sum of the van der Waals radii can be taken as indication of the hydrogen bond strength. One scheme gives the following somewhat arbitrary classification: those that are 15 to 40 kcal/mol, 5 to 15 kcal/mol, and >0 to 5 kcal/mol are considered strong, moderate, and weak, respectively.
 * F\sH***:F- (161.5 kJ/mol or 38.6 kcal/mol), illustrated uniquely by HF2-
 * O\sH***:N (29 kJ/mol or 6.9 kcal/mol), illustrated water-ammonia
 * O\sH***:O (21 kJ/mol or 5.0 kcal/mol), illustrated water-water, alcohol-alcohol
 * N\sH***:N (13 kJ/mol or 3.1 kcal/mol), illustrated by ammonia-ammonia
 * N\sH***:O (8 kJ/mol or 1.9 kcal/mol), illustrated water-amide
 * OH3+***:OH2 (18 kJ/mol or 4.3 kcal/mol)

Hydrogen bonds involving C-H bonds are both very rare and weak.

Resonance assisted hydrogen bond
The resonance assisted hydrogen bond (commonly abbreviated as RAHB) is a strong type of hydrogen bond. It is characterized by the π-delocalization that involves the hydrogen and cannot be properly described by the electrostatic model alone. This description of the hydrogen bond has been proposed to describe unusually short distances generally observed between O\dC\sOH*** or ***O\dC\sC\dC\sOH.

Structural details
The X\sH distance is typically ≈110 pm, whereas the H***Y distance is ≈160 to 200 pm. The typical length of a hydrogen bond in water is 197 pm. The ideal bond angle depends on the nature of the hydrogen bond donor. The following hydrogen bond angles between a hydrofluoric acid donor and various acceptors have been determined experimentally:

Spectroscopy
Strong hydrogen bonds are revealed by downfield shifts in the 1H NMR spectrum. For example, the acidic proton in the enol tautomer of acetylacetone appears at $\delta_\text{H}$ 15.5, which is about 10 ppm downfield of a conventional alcohol.

In the IR spectrum, hydrogen bonding shifts the X\sH stretching frequency to lower energy (i.e. the vibration frequency decreases). This shift reflects a weakening of the X\sH bond. Certain hydrogen bonds - improper hydrogen bonds - show a blue shift of the X\sH stretching frequency and a decrease in the bond length. H-bonds can also be measured by IR vibrational mode shifts of the acceptor. The amide I mode of backbone carbonyls in α-helices shifts to lower frequencies when they form H-bonds with side-chain hydroxyl groups. The dynamics of hydrogen bond structures in water can be probed by this OH stretching vibration. In the hydrogen bonding network in protic organic ionic plastic crystals (POIPCs), which are a type of phase change material exhibiting solid-solid phase transitions prior to melting, variable-temperature infrared spectroscopy can reveal the temperature dependence of hydrogen bonds and the dynamics of both the anions and the cations. The sudden weakening of hydrogen bonds during the solid-solid phase transition seems to be coupled with the onset of orientational or rotational disorder of the ions.

Theoretical considerations
Hydrogen bonding is of persistent theoretical interest. According to a modern description O:H\sO integrates both the intermolecular O:H lone pair ":" nonbond and the intramolecular H\sO polar-covalent bond associated with O\sO repulsive coupling.

Quantum chemical calculations of the relevant interresidue potential constants (compliance constants) revealed large differences between individual H bonds of the same type. For example, the central interresidue N\sH***N hydrogen bond between guanine and cytosine is much stronger in comparison to the N\sH***N bond between the adenine-thymine pair.

Theoretically, the bond strength of the hydrogen bonds can be assessed using NCI index, non-covalent interactions index, which allows a visualization of these non-covalent interactions, as its name indicates, using the electron density of the system.

Interpretations of the anisotropies in the Compton profile of ordinary ice claim that the hydrogen bond is partly covalent. However, this interpretation was challenged.

Most generally, the hydrogen bond can be viewed as a metric-dependent electrostatic scalar field between two or more intermolecular bonds. This is slightly different from the intramolecular bound states of, for example, covalent or ionic bonds. However, hydrogen bonding is generally still a bound state phenomenon, since the interaction energy has a net negative sum. The initial theory of hydrogen bonding proposed by Linus Pauling suggested that the hydrogen bonds had a partial covalent nature. This interpretation remained controversial until NMR techniques demonstrated information transfer between hydrogen-bonded nuclei, a feat that would only be possible if the hydrogen bond contained some covalent character.

History
The concept of hydrogen bonding once was challenging. Linus Pauling credits T. S. Moore and T. F. Winmill with the first mention of the hydrogen bond, in 1912. Moore and Winmill used the hydrogen bond to account for the fact that trimethylammonium hydroxide is a weaker base than tetramethylammonium hydroxide. The description of hydrogen bonding in its better-known setting, water, came some years later, in 1920, from Latimer and Rodebush. In that paper, Latimer and Rodebush cited the work of a fellow scientist at their laboratory, Maurice Loyal Huggins, saying, "Mr. Huggins of this laboratory in some work as yet unpublished, has used the idea of a hydrogen kernel held between two atoms as a theory in regard to certain organic compounds."

Water
An ubiquitous example of a hydrogen bond is found between water molecules. In a discrete water molecule, there are two hydrogen atoms and one oxygen atom. The simplest case is a pair of water molecules with one hydrogen bond between them, which is called the water dimer and is often used as a model system. When more molecules are present, as is the case with liquid water, more bonds are possible because the oxygen of one water molecule has two lone pairs of electrons, each of which can form a hydrogen bond with a hydrogen on another water molecule. This can repeat such that every water molecule is H-bonded with up to four other molecules, as shown in the figure (two through its two lone pairs, and two through its two hydrogen atoms). Hydrogen bonding strongly affects the crystal structure of ice, helping to create an open hexagonal lattice. The density of ice is less than the density of water at the same temperature; thus, the solid phase of water floats on the liquid, unlike most other substances.

Liquid water's high boiling point is due to the high number of hydrogen bonds each molecule can form, relative to its low molecular mass. Owing to the difficulty of breaking these bonds, water has a very high boiling point, melting point, and viscosity compared to otherwise similar liquids not conjoined by hydrogen bonds. Water is unique because its oxygen atom has two lone pairs and two hydrogen atoms, meaning that the total number of bonds of a water molecule is up to four.

The number of hydrogen bonds formed by a molecule of liquid water fluctuates with time and temperature. From TIP4P liquid water simulations at 25 °C, it was estimated that each water molecule participates in an average of 3.59 hydrogen bonds. At 100 °C, this number decreases to 3.24 due to the increased molecular motion and decreased density, while at 0 °C, the average number of hydrogen bonds increases to 3.69. Another study found a much smaller number of hydrogen bonds: 2.357 at 25 °C. Defining and counting the hydrogen bonds is not straightforward however.

Because water may form hydrogen bonds with solute proton donors and acceptors, it may competitively inhibit the formation of solute intermolecular or intramolecular hydrogen bonds. Consequently, hydrogen bonds between or within solute molecules dissolved in water are almost always unfavorable relative to hydrogen bonds between water and the donors and acceptors for hydrogen bonds on those solutes. Hydrogen bonds between water molecules have an average lifetime of 10−11 seconds, or 10 picoseconds.

Bifurcated and over-coordinated hydrogen bonds in water
A single hydrogen atom can participate in two hydrogen bonds. This type of bonding is called "bifurcated" (split in two or "two-forked"). It can exist, for instance, in complex organic molecules. It has been suggested that a bifurcated hydrogen atom is an essential step in water reorientation.

Acceptor-type hydrogen bonds (terminating on an oxygen's lone pairs) are more likely to form bifurcation (it is called overcoordinated oxygen, OCO) than are donor-type hydrogen bonds, beginning on the same oxygen's hydrogens.

Other liquids
For example, hydrogen fluoride—which has three lone pairs on the F atom but only one H atom—can form only two bonds; (ammonia has the opposite problem: three hydrogen atoms but only one lone pair).

Further manifestations of solvent hydrogen bonding

 * Increase in the melting point, boiling point, solubility, and viscosity of many compounds can be explained by the concept of hydrogen bonding.
 * Negative azeotropy of mixtures of HF and water.
 * The fact that ice is less dense than liquid water is due to a crystal structure stabilized by hydrogen bonds.
 * Dramatically higher boiling points of NH3, H2O, and HF compared to the heavier analogues PH3, H2S, and HCl, where hydrogen-bonding is absent.
 * Viscosity of anhydrous phosphoric acid and of glycerol.
 * Dimer formation in carboxylic acids and hexamer formation in hydrogen fluoride, which occur even in the gas phase, resulting in gross deviations from the ideal gas law.
 * Pentamer formation of water and alcohols in apolar solvents.

Hydrogen bonds in polymers
Hydrogen bonding plays an important role in determining the three-dimensional structures and the properties adopted by many proteins. Compared to the C\sC, C\sO, and C\sN bonds that comprise most polymers, hydrogen bonds are far weaker, perhaps 5%. Thus, hydrogen bonds can be broken by chemical or mechanical means while retaining the basic structure of the polymer backbone. This hierarchy of bond strengths (covalent bonds being stronger than hydrogen-bonds being stronger than van der Waals forces) is relevant in the properties of many materials.

DNA

In these macromolecules, bonding between parts of the same macromolecule cause it to fold into a specific shape, which helps determine the molecule's physiological or biochemical role. For example, the double helical structure of DNA is due largely to hydrogen bonding between its base pairs (as well as pi stacking interactions), which link one complementary strand to the other and enable replication.

Proteins
In the secondary structure of proteins, hydrogen bonds form between the backbone oxygens and amide hydrogens. When the spacing of the amino acid residues participating in a hydrogen bond occurs regularly between positions i and i + 4, an alpha helix is formed. When the spacing is less, between positions i and i + 3, then a 310 helix is formed. When two strands are joined by hydrogen bonds involving alternating residues on each participating strand, a beta sheet is formed. Hydrogen bonds also play a part in forming the tertiary structure of protein through interaction of R-groups. (See also protein folding).

Bifurcated H-bond systems are common in alpha-helical transmembrane proteins between the backbone amide C\dO of residue i as the H-bond acceptor and two H-bond donors from residue i + 4: the backbone amide N\sH and a side-chain hydroxyl or thiol H+. The energy preference of the bifurcated H-bond hydroxyl or thiol system is -3.4 kcal/mol or -2.6 kcal/mol, respectively. This type of bifurcated H-bond provides an intrahelical H-bonding partner for polar side-chains, such as serine, threonine, and cysteine within the hydrophobic membrane environments.

The role of hydrogen bonds in protein folding has also been linked to osmolyte-induced protein stabilization. Protective osmolytes, such as trehalose and sorbitol, shift the protein folding equilibrium toward the folded state, in a concentration dependent manner. While the prevalent explanation for osmolyte action relies on excluded volume effects that are entropic in nature, circular dichroism (CD) experiments have shown osmolyte to act through an enthalpic effect. The molecular mechanism for their role in protein stabilization is still not well established, though several mechanisms have been proposed. Computer molecular dynamics simulations suggest that osmolytes stabilize proteins by modifying the hydrogen bonds in the protein hydration layer.

Several studies have shown that hydrogen bonds play an important role for the stability between subunits in multimeric proteins. For example, a study of sorbitol dehydrogenase displayed an important hydrogen bonding network which stabilizes the tetrameric quaternary structure within the mammalian sorbitol dehydrogenase protein family.

A protein backbone hydrogen bond incompletely shielded from water attack is a dehydron. Dehydrons promote the removal of water through proteins or ligand binding. The exogenous dehydration enhances the electrostatic interaction between the amide and carbonyl groups by de-shielding their partial charges. Furthermore, the dehydration stabilizes the hydrogen bond by destabilizing the nonbonded state consisting of dehydrated isolated charges.

Wool, being a protein fibre, is held together by hydrogen bonds, causing wool to recoil when stretched. However, washing at high temperatures can permanently break the hydrogen bonds and a garment may permanently lose its shape.

Other polymers

The properties of many polymers are affected by hydrogen bonds within and/or between the chains. Prominent examples include cellulose and its derived fibers, such as cotton and flax. In nylon, hydrogen bonds between carbonyl and the amide NH effectively link adjacent chains, which gives the material mechanical strength. Hydrogen bonds also affect the aramid fibre, where hydrogen bonds stabilize the linear chains laterally. The chain axes are aligned along the fibre axis, making the fibres extremely stiff and strong. Hydrogen-bond networks make both polymers sensitive to humidity levels in the atmosphere because water molecules can diffuse into the surface and disrupt the network. Some polymers are more sensitive than others. Thus nylons are more sensitive than aramids, and nylon 6 more sensitive than nylon-11.

Symmetric hydrogen bond
A symmetric hydrogen bond is a special type of hydrogen bond in which the proton is spaced exactly halfway between two identical atoms. The strength of the bond to each of those atoms is equal. It is an example of a three-center four-electron bond. This type of bond is much stronger than a "normal" hydrogen bond. The effective bond order is 0.5, so its strength is comparable to a covalent bond. It is seen in ice at high pressure, and also in the solid phase of many anhydrous acids such as hydrofluoric acid and formic acid at high pressure. It is also seen in the bifluoride ion [F***H***F]-. Due to severe steric constraint, the protonated form of Proton Sponge (1,8-bis(dimethylamino)naphthalene) and its derivatives also have symmetric hydrogen bonds ([N***H***N]+), although in the case of protonated Proton Sponge, the assembly is bent.

Dihydrogen bond
The hydrogen bond can be compared with the closely related dihydrogen bond, which is also an intermolecular bonding interaction involving hydrogen atoms. These structures have been known for some time, and well characterized by crystallography; however, an understanding of their relationship to the conventional hydrogen bond, ionic bond, and covalent bond remains unclear. Generally, the hydrogen bond is characterized by a proton acceptor that is a lone pair of electrons in nonmetallic atoms (most notably in the nitrogen, and chalcogen groups). In some cases, these proton acceptors may be pi-bonds or metal complexes. In the dihydrogen bond, however, a metal hydride serves as a proton acceptor, thus forming a hydrogen-hydrogen interaction. Neutron diffraction has shown that the molecular geometry of these complexes is similar to hydrogen bonds, in that the bond length is very adaptable to the metal complex/hydrogen donor system.

Application to drugs
The Hydrogen bond is relevant to drug design. According to Lipinski's rule of five the majority of orally active drugs have no more than five hydrogen bond donors and fewer than ten hydrogen bond acceptors. These interactions exist between nitrogen–hydrogen and oxygen–hydrogen centers. Many drugs do not, however, obey these "rules".

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

title: Hydrogen bond


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Heraldry

Heraldry is a discipline relating to the design, display and study of armorial bearings (known as armory), as well as related disciplines, such as vexillology, together with the study of ceremony, rank and pedigree. Armory, the best-known branch of heraldry, concerns the design and transmission of the heraldic achievement. The achievement, or armorial bearings usually includes a coat of arms on a shield, helmet and crest, together with any accompanying devices, such as supporters, badges, heraldic banners and mottoes.

Although the use of various devices to signify individuals and groups goes back to antiquity, both the form and use of such devices varied widely, as the concept of regular, hereditary designs, constituting the distinguishing feature of heraldry, did not develop until the High Middle Ages. It is often claimed that the use of helmets with face guards during this period made it difficult to recognize one's commanders in the field when large armies gathered together for extended periods, necessitating the development of heraldry as a symbolic language, but there is little support for this view.

The perceived beauty and pageantry of heraldic designs allowed them to survive the gradual abandonment of armour on the battlefield during the seventeenth century. Heraldry has been described poetically as "the handmaid of history", "the shorthand of history", and "the floral border in the garden of history". In modern times, individuals, public and private organizations, corporations, cities, towns, regions, and other entities use heraldry and its conventions to symbolize their heritage, achievements, and aspirations.

Precursors
Various symbols have been used to represent individuals or groups for thousands of years. The earliest representations of distinct persons and regions in Egyptian art show the use of standards topped with the images or symbols of various gods, and the names of kings appear upon emblems known as serekhs, representing the king's palace, and usually topped with a falcon representing the god Horus, of whom the king was regarded as the earthly incarnation. Similar emblems and devices are found in ancient Mesopotamian art of the same period, and the precursors of heraldic beasts such as the griffin can also be found. In the Bible, the Book of Numbers refers to the standards and ensigns of the children of Israel, who were commanded to gather beneath these emblems and declare their pedigrees. The Greek and Latin writers frequently describe the shields and symbols of various heroes, and units of the Roman army were sometimes identified by distinctive markings on their shields. At least one pre-historic European object, the Nebra sky disc, is also thought to serve as a heraldic precursor.

Until the nineteenth century, it was common for heraldic writers to cite examples such as these, and metaphorical symbols such as the "Lion of Judah" or "Eagle of the Caesars" as evidence of the antiquity of heraldry itself; and to infer therefrom that the great figures of ancient history bore arms representing their noble status and descent. The Book of Saint Albans, compiled in 1486, declares that Christ himself was a gentleman of coat armour. These claims are now regarded as the fantasy of medieval heralds, as there is no evidence of a distinctive symbolic language akin to that of heraldry during this early period; nor do many of the shields described in antiquity bear a close resemblance to those of medieval heraldry; nor is there any evidence that specific symbols or designs were passed down from one generation to the next, representing a particular person or line of descent.

The medieval heralds also devised arms for various knights and lords from history and literature. Notable examples include the toads attributed to Pharamond, the cross and martlets of Edward the Confessor, and the various arms attributed to the Nine Worthies and the Knights of the Round Table. These too are readily dismissed as fanciful inventions, rather than evidence of the antiquity of heraldry.

Origins of modern heraldry

The development of the modern heraldic language cannot be attributed to a single individual, time, or place. Although certain designs that are now considered heraldic were evidently in use during the eleventh century, most accounts and depictions of shields up to the beginning of the twelfth century contain little or no evidence of their heraldic character. For example, the Bayeux Tapestry, illustrating the Norman invasion of England in 1066, and probably commissioned about 1077, when the cathedral of Bayeux was rebuilt, depicts a number of shields of various shapes and designs, many of which are plain, while others are decorated with dragons, crosses, or other typically heraldic figures. Yet no individual is depicted twice bearing the same arms, nor are any of the descendants of the various persons depicted known to have borne devices resembling those in the tapestry.

Similarly, an account of the French knights at the court of the Byzantine emperor Alexius I at the beginning of the twelfth century describes their shields of polished metal, devoid of heraldic design. A Spanish manuscript from 1109 describes both plain and decorated shields, none of which appears to have been heraldic. The Abbey of St. Denis contained a window commemorating the knights who embarked on the Second Crusade in 1147, and was probably made soon after the event; but Montfaucon's illustration of the window before it was destroyed shows no heraldic design on any of the shields.

In England, from the time of the Norman conquest, official documents had to be sealed. Beginning in the twelfth century, seals assumed a distinctly heraldic character; a number of seals dating from between 1135 and 1155 appear to show the adoption of heraldic devices in England, France, Germany, Spain, and Italy. A notable example of an early armorial seal is attached to a charter granted by Philip I, Count of Flanders, in 1164. Seals from the latter part of the eleventh and early twelfth centuries show no evidence of heraldic symbolism, but by the end of the twelfth century, seals are uniformly heraldic in nature.

One of the earliest known examples of armory as it subsequently came to be practiced can be seen on the tomb of Geoffrey Plantagenet, Count of Anjou, who died in 1151. An enamel, probably commissioned by Geoffrey's widow between 1155 and 1160, depicts him carrying a blue shield decorated with six golden lions rampant. He wears a blue helmet adorned with another lion, and his cloak is lined in vair. A medieval chronicle states that Geoffrey was given a shield of this description when he was knighted by his father-in-law, Henry I, in 1128; but this account probably dates to about 1175.

The earlier heraldic writers attributed the lions of England to William the Conqueror, but the earliest evidence of the association of lions with the English crown is a seal bearing two lions passant, used by the future King John during the lifetime of his father, Henry II, who died in 1189. Since Henry was the son of Geoffrey Plantagenet, it seems reasonable to suppose that the adoption of lions as an heraldic emblem by Henry or his sons might have been inspired by Geoffrey's shield. John's elder brother, Richard the Lionheart, who succeeded his father on the throne, is believed to have been the first to have borne the arms of three lions passant-guardant, still the arms of England, having earlier used two lions rampant combatant, which arms may also have belonged to his father. Richard is also credited with having originated the English crest of a lion statant (now statant-guardant).

The origins of heraldry are sometimes associated with the Crusades, a series of military campaigns undertaken by Christian armies from 1096 to 1487, with the goal of reconquering Jerusalem and other former Byzantine territories captured by Muslim forces during the seventh century. While there is no evidence that heraldic art originated in the course of the Crusades, there is no reason to doubt that the gathering of large armies, drawn from across Europe for a united cause, would have encouraged the adoption of armorial bearings as a means of identifying one's commanders in the field, or that it helped disseminate the principles of armory across Europe. At least two distinctive features of heraldry are generally accepted as products of the crusaders: the surcoat, an outer garment worn over the armor to protect the wearer from the heat of the sun, was often decorated with the same devices that appeared on a knight's shield. It is from this garment that the phrase "coat of arms" is derived. Also the lambrequin, or mantling, that depends from the helmet and frames the shield in modern heraldry, began as a practical covering for the helmet and the back of the neck during the Crusades, serving much the same function as the surcoat. Its slashed or scalloped edge, today rendered as billowing flourishes, is thought to have originated from hard wearing in the field, or as a means of deadening a sword blow and perhaps entangling the attacker's weapon.

Heralds and heraldic authorities
The spread of armorial bearings across Europe gave rise to a new occupation: the herald, originally a type of messenger employed by noblemen, assumed the responsibility of learning and knowing the rank, pedigree, and heraldic devices of various knights and lords, as well as the rules governing the design and description, or blazoning of arms, and the precedence of their bearers. As early as the late thirteenth century, certain heralds in the employ of monarchs were given the title "King of Heralds", which eventually became "King of Arms."

In the earliest period, arms were assumed by their bearers without any need for heraldic authority. However, by the middle of the fourteenth century, the principle that only a single individual was entitled to bear a particular coat of arms was generally accepted, and disputes over the ownership of arms seems to have led to gradual establishment of heraldic authorities to regulate their use. The earliest known work of heraldic jurisprudence, De Insigniis et Armis, was written about 1350 by Bartolus de Saxoferrato, a professor of law at the University of Padua. The most celebrated armorial dispute in English heraldry is that of Scrope v Grosvenor (1390), in which two different men claimed the right to bear azure, a bend or. The continued proliferation of arms, and the number of disputes arising from different men assuming the same arms, led Henry V to issue a proclamation in 1419, forbidding all those who had not borne arms at the Battle of Agincourt from assuming arms, except by inheritance or a grant from the crown.

Beginning in the reign of Henry VIII of England, the English Kings of Arms were commanded to make visitations, in which they traveled about the country, recording arms borne under proper authority, and requiring those who bore arms without authority either to obtain authority for them, or cease their use. Arms borne improperly were to be taken down and defaced. The first such visitation began in 1530, and the last was carried out in 1700, although no new commissions to carry out visitations were made after the accession of William III in 1689. There is little evidence that Scottish heralds ever went on visitations.

In 1484, during the reign of Richard III, the various heralds employed by the crown were incorporated into England's College of Arms, through which all new grants of arms would eventually be issued. The college currently consists of three Kings of Arms, assisted by six Heralds, and four Pursuivants, or junior officers of arms, all under the authority of the Earl Marshal; but all of the arms granted by the college are granted by the authority of the crown. In Scotland Court of the Lord Lyon King of Arms oversees the heraldry, and holds court sessions which are an official part of Scotland's court system. Similar bodies regulate the granting of arms in other monarchies and several members of the Commonwealth of Nations, but in most other countries there is no heraldic authority, and no law preventing anyone from assuming whatever arms they please, provided that they do not infringe upon the arms of another.

Later uses and developments
Although heraldry originated from military necessity, it soon found itself at home in the pageantry of the medieval tournament. The opportunity for knights and lords to display their heraldic bearings in a competitive medium led to further refinements, such as the development of elaborate tournament helms, and further popularized the art of heraldry throughout Europe. Prominent burghers and corporations, including many cities and towns, assumed or obtained grants of arms, with only nominal military associations. Heraldic devices were depicted in various contexts, such as religious and funerary art, and in using a wide variety of media, including stonework, carved wood, enamel, stained glass, and embroidery.

As the rise of firearms rendered the mounted knight increasingly irrelevant during the sixteenth and seventeenth centuries, and the tournament faded into history, the military character of heraldry gave way to its use as a decorative art. Freed from the limitations of actual shields and the need for arms to be easily distinguished in combat, heraldic artists designed increasingly elaborate achievements, culminating in the development of "landscape heraldry", incorporating realistic depictions of landscapes, during the latter part of the eighteenth and early part of the nineteenth century. These fell out of fashion during the mid-nineteenth century, when a renewed interest in the history of armory led to the re-evaluation of earlier designs, and a new appreciation for the medieval origins of the art. In particular, a late use of heraldic imagery has been in patriotic commemorations and nationalistic propaganda during the nineteenth and early twentieth centuries. Since the late nineteenth century, heraldry has focused on the use of varied lines of partition and little-used ordinaries to produce new and unique designs.

Elements of an achievement
A heraldic achievement consists of a shield of arms, the coat of arms, or simply coat, together with all of its accompanying elements, such as a crest, supporters, and other heraldic embellishments. The term "coat of arms" technically refers to the shield of arms itself, but the phrase is commonly used to refer to the entire achievement. The one indispensable element of a coat of arms is the shield; many ancient coats of arms consist of nothing else, but no achievement or armorial bearings exists without a coat of arms.

From a very early date, illustrations of arms were frequently embellished with helmets placed above the shields. These in turn came to be decorated with fan-shaped or sculptural crests, often incorporating elements from the shield of arms; as well as a wreath or torse, or sometimes a coronet, from which depended the lambrequin or mantling. To these elements, modern heraldry often adds a motto displayed on a ribbon, typically below the shield. The helmet is borne of right, and forms no part of a grant of arms; it may be assumed without authority by anyone entitled to bear arms, together with mantling and whatever motto the armiger may desire. The crest, however, together with the torse or coronet from which it arises, must be granted or confirmed by the relevant heraldic authority.

If the bearer is entitled to the ribbon, collar, or badge of a knightly order, it may encircle or depend from the shield. Some arms, particularly those of the nobility, are further embellished with supporters, heraldic figures standing alongside or behind the shield; often these stand on a compartment, typically a mound of earth and grass, on which other badges, symbols, or heraldic banners may be displayed. The most elaborate achievements sometimes display the entire coat of arms beneath a pavilion, an embellished tent or canopy of the type associated with the medieval tournament, though this is only very rarely found in English or Scots achievements.

Shield
The primary element of a heraldic achievement is the shield, or escutcheon, upon which the coat of arms is depicted. All of the other elements of an achievement are designed to decorate and complement these arms, but only the shield of arms is required. The shape of the shield, like many other details, is normally left to the discretion of the heraldic artist, and many different shapes have prevailed during different periods of heraldic design, and in different parts of Europe.

One shape alone is normally reserved for a specific purpose: the lozenge, a diamond-shaped escutcheon, was traditionally used to display the arms of women, on the grounds that shields, as implements of war, were inappropriate for this purpose. This distinction was not always strictly adhered to, and a general exception was usually made for sovereigns, whose arms represented an entire nation. Sometimes an oval shield, or cartouche, was substituted for the lozenge; this shape was also widely used for the arms of clerics in French, Spanish, and Italian heraldry, although it was never reserved for their use. In recent years, the use of the cartouche for women's arms has become general in Scottish heraldry, while both Scottish and Irish authorities have permitted a traditional shield under certain circumstances, and in Canadian heraldry the shield is now regularly granted.

The whole surface of the escutcheon is termed the field, which may be plain, consisting of a single tincture, or divided into multiple sections of differing tinctures by various lines of partition; and any part of the field may be semé, or powdered with small charges. The edges and adjacent parts of the escutcheon are used to identify the placement of various heraldic charges; the upper edge, and the corresponding upper third of the shield, are referred to as the chief; the lower part is the base. The sides of the shield are known as the dexter and sinister flanks, although these terms are based on the point of view of the bearer of the shield, who would be standing behind it; to the observer, and in all heraldic illustration, the dexter is on the left side, and the sinister on the right.

The placement of various charges may also refer to a number of specific points, nine in number according to some authorities, but eleven according to others. The three most important are fess point, located in the visual center of the shield; the honour point, located midway between fess point and the chief; and the nombril point, located midway between fess point and the base. The other points include dexter chief, center chief, and sinister chief, running along the upper part of the shield from left to right, above the honour point; dexter flank and sinister flank, on the sides approximately level with fess point; and dexter base, middle base, and sinister base along the lower part of the shield, below the nombril point.

Tinctures
One of the most distinctive qualities of heraldry is the use of a limited palette of colours and patterns, usually referred to as tinctures. These are divided into three categories, known as metals, colours, and furs.

The metals are or and argent, representing gold and silver, respectively, although in practice they are usually depicted as yellow and white. Five colours are universally recognized: gules, or red; sable, or black; azure, or blue; vert, or green; and purpure, or purple; and most heraldic authorities also admit two additional colours, known as sanguine or murrey, a dark red or mulberry colour between gules and purpure, and tenné, an orange or dark yellow to brown colour. These last two are quite rare, and are often referred to as stains, from the belief that they were used to represent some dishonourable act, although in fact there is no evidence that this use existed outside of fanciful heraldic writers. Perhaps owing to the realization that there is really no such thing as a stain in genuine heraldry, as well as the desire to create new and unique designs, the use of these colours for general purposes has become accepted in the twentieth and twenty-first centuries. Occasionally one meets with other colours, particularly in continental heraldry, although they are not generally regarded among the standard heraldic colours. Among these are cendrée, or ash-colour; brunâtre, or brown; bleu-céleste or bleu de ciel, sky blue; amaranth or columbine, a bright violet-red or pink colour; and carnation, commonly used to represent flesh in French heraldry. A more recent addition is the use of copper as a metal in one or two Canadian coats of arms.

There are two basic types of heraldic fur, known as ermine and vair, but over the course of centuries each has developed a number of variations. Ermine represents the fur of the stoat, a type of weasel, in its white winter coat, when it is called an ermine. It consists of a white, or occasionally silver field, powdered with black figures known as ermine spots, representing the black tip of the animal's tail. Ermine was traditionally used to line the cloaks and caps of the nobility. The shape of the heraldic ermine spot has varied considerably over time, and nowadays is typically drawn as an arrowhead surmounted by three small dots, but older forms may be employed at the artist's discretion. When the field is sable and the ermine spots argent, the same pattern is termed ermines; when the field is or rather than argent, the fur is termed erminois; and when the field is sable and the ermine spots or, it is termed pean.

Vair represents the winter coat of the red squirrel, which is blue-grey on top and white underneath. To form the linings of cloaks, the pelts were sewn together, forming an undulating, bell-shaped pattern, with interlocking light and dark rows. The heraldic fur is depicted with interlocking rows of argent and azure, although the shape of the pelts, usually referred to as "vair bells", is usually left to the artist's discretion. In the modern form, the bells are depicted with straight lines and sharp angles, and meet only at points; in the older, undulating pattern, now known as vair ondé or vair ancien, the bells of each tincture are curved and joined at the base. There is no fixed rule as to whether the argent bells should be at the top or the bottom of each row. At one time vair commonly came in three sizes, and this distinction is sometimes encountered in continental heraldry; if the field contains fewer than four rows, the fur is termed gros vair or beffroi; if of six or more, it is menu-vair, or miniver.

A common variation is counter-vair, in which alternating rows are reversed, so that the bases of the vair bells of each tincture are joined to those of the same tincture in the row above or below. When the rows are arranged so that the bells of each tincture form vertical columns, it is termed vair in pale; in continental heraldry one may encounter vair in bend, which is similar to vair in pale, but diagonal. When alternating rows are reversed as in counter-vair, and then displaced by half the width of one bell, it is termed vair in point, or wave-vair. A form peculiar to German heraldry is alternate vair, in which each vair bell is divided in half vertically, with half argent and half azure. All of these variations can also be depicted in the form known as potent, in which the shape of the vair bell is replaced by a T-shaped figure, known as a potent from its resemblance to a crutch. Although it is really just a variation of vair, it is frequently treated as a separate fur.

When the same patterns are composed of tinctures other than argent and azure, they are termed vairé or vairy of those tinctures, rather than vair; potenté of other colours may also be found. Usually vairé will consist of one metal and one colour, but ermine or one of its variations may also be used, and vairé of four tinctures, usually two metals and two colours, is sometimes found.

Three additional furs are sometimes encountered in continental heraldry; in French and Italian heraldry one meets with plumeté or plumetty, in which the field appears to be covered with feathers, and papelonné, in which it is decorated with scales. In German heraldry one may encounter kursch, or vair bellies, depicted as brown and furry; all of these probably originated as variations of vair.

Considerable latitude is given to the heraldic artist in depicting the heraldic tinctures; there is no fixed shade or hue to any of them.

Whenever an object is depicted as it appears in nature, rather than in one or more of the heraldic tinctures, it is termed proper, or the colour of nature. This does not seem to have been done in the earliest heraldry, but examples are known from at least the seventeenth century. While there can be no objection to the occasional depiction of objects in this manner, the overuse of charges in their natural colours is often cited as indicative of bad heraldic practice. The practice of landscape heraldry, which flourished in the latter part of the eighteenth and early part of the nineteenth century, made extensive use of non-heraldic colours.

One of the most important conventions of heraldry is the so-called "rule of tincture". To provide for contrast and visibility, metals should never be placed on metals, and colours should never be placed on colours. This rule does not apply to charges which cross a division of the field, which is partly metal and partly colour; nor, strictly speaking, does it prevent a field from consisting of two metals or two colours, although this is unusual. Furs are considered amphibious, and neither metal nor colour; but in practice ermine and erminois are usually treated as metals, while ermines and pean are treated as colours. This rule is strictly adhered to in British armory, with only rare exceptions; although generally observed in continental heraldry, it is not adhered to quite as strictly. Arms which violate this rule are sometimes known as "puzzle arms", of which the most famous example is the arms of the Kingdom of Jerusalem, consisting of gold crosses on a silver field.

Variations of the field
The field of a shield, or less often a charge or crest, is sometimes made up of a pattern of colours, or variation. A pattern of horizontal (barwise) stripes, for example, is called barry, while a pattern of vertical (palewise) stripes is called paly. A pattern of diagonal stripes may be called bendy or bendy sinister, depending on the direction of the stripes. Other variations include chevrony, gyronny and chequy. Wave shaped stripes are termed undy. For further variations, these are sometimes combined to produce patterns of barry-bendy, paly-bendy, lozengy and fusilly. Semés, or patterns of repeated charges, are also considered variations of the field. The Rule of tincture applies to all semés and variations of the field.

Divisions of the field

The field of a shield in heraldry can be divided into more than one tincture, as can the various heraldic charges. Many coats of arms consist simply of a division of the field into two contrasting tinctures. These are considered divisions of a shield, so the rule of tincture can be ignored. For example, a shield divided azure and gules would be perfectly acceptable. A line of partition may be straight or it may be varied. The variations of partition lines can be wavy, indented, embattled, engrailed, nebuly, or made into myriad other forms; see Line (heraldry).

Ordinaries
In the early days of heraldry, very simple bold rectilinear shapes were painted on shields. These could be easily recognized at a long distance and could be easily remembered. They therefore served the main purpose of heraldry: identification. As more complicated shields came into use, these bold shapes were set apart in a separate class as the "honourable ordinaries". They act as charges and are always written first in blazon. Unless otherwise specified they extend to the edges of the field. Though ordinaries are not easily defined, they are generally described as including the cross, the fess, the pale, the bend, the chevron, the saltire, and the pall.

There is a separate class of charges called sub-ordinaries which are of a geometrical shape subordinate to the ordinary. According to Friar, they are distinguished by their order in blazon. The sub-ordinaries include the inescutcheon, the orle, the tressure, the double tressure, the bordure, the chief, the canton, the label, and flaunches.

Ordinaries may appear in parallel series, in which case blazons in English give them different names such as pallets, bars, bendlets, and chevronels. French blazon makes no such distinction between these diminutives and the ordinaries when borne singly. Unless otherwise specified an ordinary is drawn with straight lines, but each may be indented, embattled, wavy, engrailed, or otherwise have their lines varied.

Charges
A charge is any object or figure placed on a heraldic shield or on any other object of an armorial composition. Any object found in nature or technology may appear as a heraldic charge in armory. Charges can be animals, objects, or geometric shapes. Apart from the ordinaries, the most frequent charges are the cross – with its hundreds of variations – and the lion and eagle. Other common animals are bears, stags, wild boars, martlets, wolves and fish. Dragons, bats, unicorns, griffins, and other monsters appear as charges and as supporters.

Animals are found in various stereotyped positions or attitudes. Quadrupeds can often be found rampant (standing on the left hind foot). Another frequent position is passant, or walking, like the lions of the coat of arms of England. Eagles are almost always shown with their wings spread, or displayed. A pair of wings conjoined is called a vol.

In English heraldry the crescent, mullet, martlet, annulet, fleur-de-lis, and rose may be added to a shield to distinguish cadet branches of a family from the senior line. These cadency marks are usually shown smaller than normal charges, but it still does not follow that a shield containing such a charge belongs to a cadet branch. All of these charges occur frequently in basic undifferenced coats of arms.

Marshalling

To marshal two or more coats of arms is to combine them in one shield, to express inheritance, claims to property, or the occupation of an office. This can be done in a number of ways, of which the simplest is impalement: dividing the field per pale and putting one whole coat in each half. Impalement replaced the earlier dimidiation – combining the dexter half of one coat with the sinister half of another – because dimidiation can create ambiguity between, for example, a bend and a chevron. "Dexter" (from Latin dextra, "right") means to the right from the viewpoint of the bearer of the arms and "sinister" (from Latin sinistra, "left") means to the bearer's left. The dexter side is considered the side of greatest honour (see also dexter and sinister).

A more versatile method is quartering, division of the field by both vertical and horizontal lines. This practice originated in Spain (Castile and León) after the 13th century. As the name implies, the usual number of divisions is four, but the principle has been extended to very large numbers of "quarters".

Quarters are numbered from the dexter chief (the corner nearest to the right shoulder of a man standing behind the shield), proceeding across the top row, and then across the next row and so on. When three coats are quartered, the first is repeated as the fourth; when only two coats are quartered, the second is also repeated as the third. The quarters of a personal coat of arms correspond to the ancestors from whom the bearer has inherited arms, normally in the same sequence as if the pedigree were laid out with the father's father's ... father (to as many generations as necessary) on the extreme left and the mother's mother's...mother on the extreme right. A few lineages have accumulated hundreds of quarters, though such a number is usually displayed only in documentary contexts. The Scottish and Spanish traditions resist allowing more than four quarters, preferring to subdivide one or more "grand quarters" into sub-quarters as needed.

The third common mode of marshalling is with an inescutcheon, a small shield placed in front of the main shield. In Britain this is most often an "escutcheon of pretence" indicating, in the arms of a married couple, that the wife is an heraldic heiress (i.e., she inherits a coat of arms because she has no brothers). In continental Europe an inescutcheon (sometimes called a "heart shield") usually carries the ancestral arms of a monarch or noble whose domains are represented by the quarters of the main shield.

In German heraldry, animate charges in combined coats usually turn to face the centre of the composition.

Helm and crest
In English the word "crest" is commonly (but erroneously) used to refer to an entire heraldic achievement of armorial bearings. The technical use of the heraldic term crest refers to just one component of a complete achievement. The crest rests on top of a helmet which itself rests on the most important part of the achievement: the shield.

The modern crest has grown out of the three-dimensional figure placed on the top of the mounted knights' helms as a further means of identification. In most heraldic traditions, a woman does not display a crest, though this tradition is being relaxed in some heraldic jurisdictions, and the stall plate of Lady Marion Fraser in the Thistle Chapel in St Giles, Edinburgh, shows her coat on a lozenge but with helmet, crest, and motto.

The crest is usually found on a wreath of twisted cloth and sometimes within a coronet. Crest-coronets are generally simpler than coronets of rank, but several specialized forms exist; for example, in Canada, descendants of the United Empire Loyalists are entitled to use a Loyalist military coronet (for descendants of members of Loyalist regiments) or Loyalist civil coronet (for others).

When the helm and crest are shown, they are usually accompanied by a mantling. This was originally a cloth worn over the back of the helmet as partial protection against heating by sunlight. Today it takes the form of a stylized cloak hanging from the helmet. Typically in British heraldry, the outer surface of the mantling is of the principal colour in the shield and the inner surface is of the principal metal, though peers in the United Kingdom use standard colourings (Gules doubled Argent - Red/White) regardless of rank or the colourings of their arms. The mantling is sometimes conventionally depicted with a ragged edge, as if damaged in combat, though the edges of most are simply decorated at the emblazoner's discretion.

Clergy often refrain from displaying a helm or crest in their heraldic achievements. Members of the clergy may display appropriate headwear. This often takes the form of a small crowned, wide brimmed hat called a galero with the colours and tassels denoting rank; or, in the case of Papal coats of arms until the inauguration of Pope Benedict XVI in 2005, an elaborate triple crown known as a tiara. Benedict broke with tradition to substitute a mitre in his arms. Orthodox and Presbyterian clergy do sometimes adopt other forms of headgear to ensign their shields. In the Anglican tradition, clergy members may pass crests on to their offspring, but rarely display them on their own shields.

Mottoes
An armorial motto is a phrase or collection of words intended to describe the motivation or intention of the armigerous person or corporation. This can form a pun on the family name as in Thomas Nevile's motto Ne vile velis. Mottoes are generally changed at will and do not make up an integral part of the armorial achievement. Mottoes can typically be found on a scroll under the shield. In Scottish heraldry, where the motto is granted as part of the blazon, it is usually shown on a scroll above the crest, and may not be changed at will. A motto may be in any language.

Supporters and other insignia
Supporters are human or animal figures or, very rarely, inanimate objects, usually placed on either side of a coat of arms as though supporting it. In many traditions, these have acquired strict guidelines for use by certain social classes. On the European continent, there are often fewer restrictions on the use of supporters. In the United Kingdom, only peers of the realm, a few baronets, senior members of orders of knighthood, and some corporate bodies are granted supporters. Often, these can have local significance or a historical link to the armiger.

If the armiger has the title of baron, hereditary knight, or higher, he may display a coronet of rank above the shield. In the United Kingdom, this is shown between the shield and helmet, though it is often above the crest in Continental heraldry.

Another addition that can be made to a coat of arms is the insignia of a baronet or of an order of knighthood. This is usually represented by a collar or similar band surrounding the shield. When the arms of a knight and his wife are shown in one achievement, the insignia of knighthood surround the husband's arms only, and the wife's arms are customarily surrounded by an ornamental garland of leaves for visual balance.

Differencing and cadency
Since arms pass from parents to offspring, and there is frequently more than one child per couple, it is necessary to distinguish the arms of siblings and extended family members from the original arms as passed on from eldest son to eldest son. Over time several schemes have been used.

Blazon
To "blazon" arms means to describe them using the formal language of heraldry. This language has its own vocabulary and syntax, or rules governing word order, which becomes essential for comprehension when blazoning a complex coat of arms. The verb comes from the Middle English blasoun, itself a derivative of the French blason meaning "shield". The system of blazoning arms used in English-speaking countries today was developed by heraldic officers in the Middle Ages. The blazon includes a description of the arms contained within the escutcheon or shield, the crest, supporters where present, motto and other insignia. Complex rules, such as the rule of tincture, apply to the physical and artistic form of newly created arms, and a thorough understanding of these rules is essential to the art of heraldry. Though heraldic forms initially were broadly similar across Europe, several national styles had developed by the end of the Middle Ages, and artistic and blazoning styles today range from the very simple to extraordinarily complex.

National styles
The emergence of heraldry occurred across western Europe almost simultaneously in the various countries. Originally, heraldic style was very similar from country to country. Over time, heraldic tradition diverged into four broad styles: German-Nordic, Gallo-British, Latin, and Eastern. In addition, it can be argued that newer national heraldic traditions, such as South African and Canadian heraldry, have emerged in the 20th century.

German-Nordic heraldry

Coats of arms in Germany, the Nordic countries, Estonia, Latvia, the Czech lands and northern Switzerland generally change very little over time. Marks of difference are very rare in this tradition, as are heraldic furs. One of the most striking characteristics of German-Nordic heraldry is the treatment of the crest. Often, the same design is repeated in the shield and the crest. The use of multiple crests is also common. The crest is rarely used separately as in British heraldry, but can sometimes serve as a mark of difference between different branches of a family. Torse is optional. Heraldic courtoisie is observed: that is, charges in a composite shield (or two shields displayed together) usually turn to face the centre.

Coats consisting only of a divided field are somewhat more frequent in Germany than elsewhere.

Dutch heraldry
The Low Countries were great centres of heraldry in medieval times. One of the famous armorials is the Gelre Armorial or Wapenboek, written between 1370 and 1414. Coats of arms in the Netherlands were not controlled by an official heraldic system like the two in the United Kingdom, nor were they used solely by noble families. Any person could develop and use a coat of arms if they wished to do so, provided they did not usurp someone else's arms, and historically, this right was enshrined in Roman Dutch law. As a result, many merchant families had coats of arms even though they were not members of the nobility. These are sometimes referred to as burgher arms, and it is thought that most arms of this type were adopted while the Netherlands was a republic (1581–1806). This heraldic tradition was also exported to the erstwhile Dutch colonies. Dutch heraldry is characterised by its simple and rather sober style, and in this sense, is closer to its medieval origins than the elaborate styles which developed in other heraldic traditions.

Gallo-British heraldry
The use of cadency marks to difference arms within the same family and the use of semy fields are distinctive features of Gallo-British heraldry (in Scotland the most significant mark of cadency being the bordure, the small brisures playing a very minor role). Marks of cadency are mandatory in Scotland, where no two persons can own identical arms at a time. It is common to see heraldic furs used. In the United Kingdom, the style is notably still controlled by royal officers of arms. French heraldry experienced a period of strict rules of construction under Napoleon. English and Scots heraldries make greater use of supporters than other European countries.

Latin heraldry
The heraldry of southern France, Andorra, Spain, and Italy is characterized by a lack of crests, and uniquely shaped shields. Portuguese heraldry, however, does use crests. Portuguese and Spanish heraldry, which together form a larger Iberian tradition of heraldry, occasionally introduce words to the shield of arms, a practice usually avoided in British heraldry. Latin heraldry is known for extensive use of quartering, because of armorial inheritance via the male and the female lines. Moreover, Italian heraldry is dominated by the Roman Catholic Church, featuring many shields and achievements, most bearing some reference to the Church.

Trees are frequent charges in Latin arms. Charged bordures, including bordures inscribed with words, are seen often in Spain.

Eastern European heraldry

Eastern European heraldry is in the traditions developed in Albania, Belarus, Bulgaria, Croatia, Hungary, Lithuania, Poland, Romania, Russia, Serbia, Slovakia and Ukraine. Eastern coats of arms are characterized by a pronounced, territorial, clan system – often, entire villages or military groups were granted the same coat of arms irrespective of family relationships. In Poland, nearly six hundred unrelated families are known to bear the same Jastrzębiec coat of arms. Marks of cadency are almost unknown, and shields are generally very simple, with only one charge. Many heraldic shields derive from ancient house marks. At least fifteen per cent of all Hungarian personal arms bear a severed Turk's head, referring to their wars against the Ottoman Empire.

Quasi-heraldic emblems
True heraldry, as now generally understood, has its roots in medieval Europe. However, there have been other historical cultures which have used symbols and emblems to represent families or individuals, and in some cases these symbols have been adopted into Western heraldry. For example, the coat of arms of the Ottoman Empire incorporated the royal tughra as part of its crest, along with such traditional Western heraldic elements as the escutcheon and the compartment.

Greek symbols
Ancient Greeks were among the first civilizations to use symbols consistently in order to identify a warrior, clan or a state. The first record of a shield blazon is illustrated in Aeschylus' tragedy Seven Against Thebes.

Mon
Mon (紋), also monshō (紋章), mondokoro (紋所), and kamon (家紋), are Japanese emblems used to decorate and identify an individual or family. While mon is an encompassing term that may refer to any such device, kamon and mondokoro refer specifically to emblems used to identify a family. An authoritative mon reference compiles Japan's 241 general categories of mon based on structural resemblance (a single mon may belong to multiple categories), with 5116 distinct individual mon (it is however well acknowledged that there exist lost or obscure mon that are not in this compilation).

The devices are similar to the badges and coats of arms in European heraldic tradition, which likewise are used to identify individuals and families. Mon are often referred to as crests in Western literature, another European heraldic device similar to the mon in function.

Japanese helmets (kabuto) also incorporated elements similar to crests, called datemono, which helped identify the wearer while they were concealed by armour. These devices sometimes incorporated mon, and some figures, like Date Masamune, were well-known for their helmet designs.

Socialist emblems
Communist states often followed a unique style characterized by communist symbolism. Although commonly called coats of arms, most such devices are not actually coats of arms in the traditional heraldic sense and should therefore, in a strict sense, not be called arms at all. Many communist governments purposely diverged from the traditional forms of European heraldry in order to distance themselves from the monarchies that they usually replaced, with actual coats of arms being seen as symbols of the monarchs.

The Soviet Union was the first state to use this type of emblem, beginning at its creation in 1922. The style became more widespread after World War II, when many other communist states were established. Even a few non-socialist states have adopted the style, for various reasons—usually because communists had helped them to gain independence—but also when no apparent connection to a Communist nation exists, such as the emblem of Italy. After the fall of the Soviet Union and the other communist states in Eastern Europe in 1989–1991, this style of heraldry was often abandoned for the old heraldic practices, with many new governments reinstating the traditional heraldry that was previously cast aside.

Tamgas
A tamga or tamgha "stamp, seal" (тамга, Turkic: tamga) is an abstract seal or stamp used by Eurasian nomadic peoples and by cultures influenced by them. The tamga was normally the emblem of a particular tribe, clan or family. They were common among the Eurasian nomads throughout Classical Antiquity and the Middle Ages (including Alans, Mongols, Sarmatians, Scythians and Turkic peoples). Similar "tamga-like" symbols were sometimes also adopted by sedentary peoples adjacent to the Pontic-Caspian steppe both in Eastern Europe and Central Asia, such as the East Slavs, whose ancient royal symbols are sometimes referred to as "tamgas" and have similar appearance.

Unlike European coats of arms, tamgas were not always inherited, and could stand for families or clans (for example, when denoting territory, livestock, or religious items) as well as for specific individuals (such as when used for weapons, or for royal seals). One could also adopt the tamga of one's master or ruler, therefore signifying said master's patronage. Outside of denoting ownership, tamgas also possessed religious significance, and were used as talismans to protect one from curses (it was believed that, as symbols of family, tamgas embodied the power of one's heritage). Tamgas depicted geometric shapes, images of animals, items, or glyphs. As they were usually inscribed using heavy and unwieldy instruments, such as knives or brands, and on different surfaces (meaning that their appearance could vary somewhat), tamgas were always simple and stylised, and needed to be laconic and easily recognisable.

Tughras
Every sultan of the Ottoman Empire had his own monogram, called the tughra, which served as a royal symbol. A coat of arms in the European heraldic sense was created in the late 19th century. Hampton Court requested from Ottoman Empire the coat of arms to be included in their collection. As the coat of arms had not been previously used in Ottoman Empire, it was designed after this request and the final design was adopted by Sultan Abdul Hamid II on April 17, 1882. It included two flags: the flag of the Ottoman Dynasty, which had a crescent and a star on red base, and the flag of the Islamic Caliph, which had three crescents on a green base.

Ancient Iran
The word of "arms" in the Pahlavi scripts is 𐭥𐭢𐭱𐭠𐭥 which is read as nišān (Persian: نشان). In Islamic sources there are some references to the existence of nišāns in ancient Iran. It is suggested that the words arms, mon, and nišān are oscillating on a same semantic context as they all satisfy a similar need: Heraldic identification. al-Masudi writes that nišāns (Arabic: شعار) used by Parthians and Sasanians. When al-Masudi talks about Sasanians, he describes their arms as "flags of Persians and their emblems" (رایات الفرس و أعلامهم). In the world of "pahlavans" (پهلوانان) of Iranian national narratives, as same as the world of European knights, each army under the command of a pahlavan from one of the noble families identified by a nišān on its flag. Usually, when the pahlavans were presented in the court of the king of Iran, they were distinguishing each troop from another with a flag which had their lords' nišāns on itself.

Modern heraldry
Today, institutions, companies, and private persons continue using coats of arms as their pictorial identification. In the United Kingdom and Ireland, the English Kings of Arms, Scotland's Lord Lyon King of Arms, and the Chief Herald of Ireland continue making grants of arms. There are heraldic authorities in Canada (Canadian Heraldic Authority), South Africa, Spain, and Sweden that grant or register coats of arms. In South Africa, the right to armorial bearings is also determined by Roman Dutch law, due to its origins as a 17th-century colony of the Netherlands.

Heraldic societies abound in Africa, Asia, Australasia, the Americas and Europe. Heraldry aficionados participate in the Society for Creative Anachronism, medieval revivals, micronations and other related projects. Modern armigers use heraldry to express ancestral and personal heritage as well as professional, academic, civic, and national pride. Little is left of class identification in modern heraldry, where the emphasis is more than ever on expression of identity.

Heraldry continues to build on its rich tradition in academia, government, guilds and professional associations, religious institutions, and the military. Nations and their subdivisions – provinces, states, counties, cities, etc. – continue to build on the traditions of civic heraldry. The Roman Catholic Church, Anglican churches, and other religious institutions maintain the traditions of ecclesiastical heraldry for clergy, religious orders, and schools.

Many of these institutions have begun to employ blazons representing modern objects. For example, some heraldic symbols issued by the United States Army Institute of Heraldry incorporate symbols such as guns, airplanes, or locomotives. Some scientific institutions incorporate symbols of modern science such as the atom or particular scientific instruments. The arms of the United Kingdom Atomic Energy Authority uses traditional heraldic symbols to depict the harnessing of atomic power. Locations with strong associations to particular industries may incorporate associated symbols. The coat of arms of Stenungsund Municipality in Sweden incorporates a hydrocarbon molecule, alluding to the historical significance of the petrochemical industry in the region.

Heraldry in countries with heraldic authorities continues to be regulated generally by laws granting rights to arms and recognizing possession of arms as well as protecting against their misuse. Countries without heraldic authorities usually treat coats of arms as creative property in the manner of logos, offering protection under copyright laws. This is the case in Nigeria, where most of the components of its heraldic system are otherwise unregulated.

title: Heraldry


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Heretic (video game)

Heretic is a dark fantasy first-person shooter video game released in December 1994. It was developed by Raven Software and published by id Software through GT Interactive.

Using a modified version of the Doom engine, Heretic was one of the first first-person games to feature inventory manipulation and the ability to look up and down. It also introduced multiple gib objects that spawned when a character suffered a death by extreme force or heat. Previously, the character would simply crumple into a heap. The game used randomised ambient sounds and noises, such as evil laughter, chains rattling, distantly ringing bells, and water dripping in addition to the background music to further enhance the atmosphere. The music in the game was composed by Kevin Schilder. An indirect sequel, Hexen: Beyond Heretic, was released the following year. Heretic II was released in 1998, which served as a direct sequel continuing the story.

Plot
Three brothers (D'Sparil, Korax, and Eidolon), known as the Serpent Riders, have used their powerful magic to possess seven kings of Parthoris, turning them into mindless puppets and corrupting their armies. The Sidhe elves resist the Serpent Riders' magic. The Serpent Riders thus declared the Sidhe as heretics and waged war against them. The Sidhe are forced to take a drastic measure to sever the natural power of the kings destroying them and their armies, but at the cost of weakening the elves' power, giving the Serpent Riders an advantage to slay the elders. While the Sidhe retreat, one elf (revealed to be named Corvus in Heretic II) sets off on a quest of vengeance against the weakest of the three Serpent Riders, D'Sparil. He travels through the "City of the Damned", the ruined capital of the Sidhe (its real name is revealed to be Silverspring in Heretic II), then past the demonic breeding grounds of Hell's Maw and finally the secret Dome of D'Sparil.

The player is the elvish protagonist Corvus and must first fight through the undead hordes infesting the location where the elders performed their ritual. At its end is the gateway to Hell's Maw, guarded by the Iron Liches. After defeating them, the player must seal the portal and so prevent further infestation, but after he enters the portal guarded by the Maulotaurs, he finds himself inside D'Sparil's dome. After killing D'Sparil, Corvus ends up on a perilous journey with little hope of returning home. However, he eventually succeeds in his endeavour, only to find that Parthoris is in disarray once again.

Gameplay
The gameplay of Heretic is heavily derived from Doom, with a level-based structure and an emphasis on finding the proper keys to progress. Many weapons are similar to those from Doom; the early weapons in particular are near-exact copies in functionality to those seen in Doom. Raven added a number of features to Heretic that differentiated it from Doom, notably interactive environments, such as rushing water that pushes the player along, and inventory items. In Heretic, the player can pick up many different items to use at their discretion. These items range from health potions to the "morph ovum", which transforms enemies into chickens. One of the most notable pickups that can be found is the "Tome of Power" which acts as a secondary firing mode for certain weapons, resulting in a much more powerful projectile from each weapon, some of which change the look of the projectile entirely. Heretic also features an improved version of the Doom engine, sporting the ability to look up and down within constraints, as well as fly. However, the rendering method for looking up and down merely uses a proportional pixel-shearing effect rather than any new rendering algorithm, which distorts the view considerably when looking at high-elevation angles.

As with Doom, Heretic contains various cheat codes that allow the player to be invulnerable, obtain every weapon, be able to instantly kill every monster in a particular level, and several other abilities. If the player uses the "all weapons and keys" cheat (" ") from Doom, a message appears warning the player against cheating and takes away all of their weapons, leaving them with only a quarterstaff. If the player uses the "god mode" cheat (" ") from Doom, the game will display a message saying "Trying to cheat, eh? Now you die!" and kills the player character.

The original shareware release of Heretic came bundled with support for online multiplayer through the new DWANGO service.

Development
Heretic was developed by Raven Software with assistance by publisher id Software, the latter of which had recently pioneered the first-person shooter genre with Wolfenstein 3D and Doom. Brian Raffel, the game's director and vice-president of Raven at the time, revealed that the developer first came to id's attention with the release of its debut title Black Crypt. After providing Raven with a modified Wolfenstein 3D engine for its next project ShadowCaster and being impressed by the final result, id requested that Raven develop a medieval-themed/dark fantasy game using a modified version of id's signature Doom engine. Raffel considered himself and his colleagues as typical D&D fans and initially drafted the game with role-playing elements. They then took instruction from id programmer John Carmack to simply "do it like Doom, and add the fantasy flavor." Heretic began development in March 1994 with Ben Gokey as lead programmer and a rough storyline penned by Michael Raymond-Judy that was finalized by the game's publisher.

id designer John Romero signed on as executive producer. He recalled visiting the team at Raven, bringing them several Intel-based Epson NeXT computers, and teaching them how to use id's tools and engine. Major additions to the engine for graphics and gameplay included an expendable inventory system; the ability to look up, look down, and fly; water and wind effects on the player character's movement; and improved audio for both ambient and localized sound. Assistant programmer Chris Rhinehart was responsible for adding the flight mechanic, which Raffel described as a "happy accident". The director explained, "Chris came up with the idea of moving the horizon line just up and down. It wasn't a real calculation of flying, it was a hack... That was such a big event for us, and that gave us our unique flavor."

Shadow of the Serpent Riders
The original version of Heretic was only available through shareware registration (i.e. mail order) and contained three episodes. The retail version, Heretic: Shadow of the Serpent Riders, was distributed by GT Interactive in 1996, and featured the original three episodes and two additional episodes: The Ossuary, which takes the player to the shattered remains of a world conquered by the Serpent Riders several centuries ago, and The Stagnant Demesne, where the player enters D'Sparil's birthplace. This version was the first official release of Heretic in Europe. A free patch was also downloadable from Raven's website to update the original Heretic with the content found in Shadow of the Serpent Riders.

Along with the two full additional episodes, Shadow of the Serpent Riders contains three additional levels in a third additional episode (unofficially known as Fate's Path) which is inaccessible without the use of cheat codes. The first of these three levels can be accessed by typing the cheat (" "). The first two levels are fully playable, but the third level does not have an exit so the player is unable to progress further.

Source release
On January 11, 1999, the source code of the game engine used in Heretic was published by Raven Software under a license that granted rights to non-commercial use, and was re-released under the GNU GPL-2.0-only on September 4, 2008. This resulted in ports to Linux, Amiga, Atari, and other operating systems, and updates to the game engine to utilize 3D acceleration. The shareware version of a console port for the Dreamcast was also released.

Reception
Heretic and Hexen shipped a combined total of roughly 1 million units by August 1997. Individually Heretic sold more than 500,000 copies.

Heretic received generally positive reviews, garnering 78% on PC Zone.

Next Generation reviewed the PC version of the game, and stated that "if you're only going to get one action game in the next couple of months, this is the one".

While remarking that Heretic is a thinly-veiled clone of Doom, and that its being released in Europe after its sequel and with Quake due out shortly makes it somewhat outdated, Maximum nonetheless regarded it as an extremely polished and worthwhile purchase. They particularly highlighted the two additional episodes of the retail version, saying they offer a satisfying challenge even to first person shooter veterans and are largely what make the game worth buying.

In 1996, Computer Gaming World listed being turned into a chicken as #3 on its list of "the 15 best ways to die in computer gaming".

Legacy
Heretic has received three sequels: Hexen: Beyond Heretic, Hexen II, and Heretic II. Following ZeniMax Media's acquisition of id Software, the rights to the series have been disputed between both id and Raven Software; Raven's parent company Activision holds the developing rights, while id holds the publishing rights to the first three games.

The game was re-released for Windows on Steam on August 3, 2007.

Further homages to the series have been made in other id Software titles; In 2009's Wolfenstein, which Raven Software developed, Heretic's Tomes of Power are collectible power-ups found throughout the game. The character Galena from Quake Champions wears armor bearing the icon of the Serpent Riders.

In 2014, Raven co-founder Brian Raffel had expressed interest in making a sequel to the Heretic series. Rather than licensing it to other developers, he wants Raven to do it themselves.

Similar to Freedoom, a free content adaptation of Heretic exists called Blasphemer.

title: Heretic (video game)