CS gas
IUPAC name 2-Chlorobenzalmalononitrile
Other names Tear gas
Identifiers
CAS number	2698-41-1 Y
ChemSpider	16644 Y
Jmol-3D images	Image 1
SMILES Clc1ccccc1\C=C(/C#N)C#N
InChI InChI=1S/C10H5ClN2/c11-10-4-2-1-3-9(10)5-8(6-12)7-13/h1-5H Y Key: JJNZXLAFIPKXIG-UHFFFAOYSA-N Y InChI=1/C10H5ClN2/c11-10-4-2-1-3-9(10)5-8(6-12)7-13/h1-5H Key: JJNZXLAFIPKXIG-UHFFFAOYAA
Properties
Molecular formula	C10H5Cl N2[2]
Molar mass	188.6 g/mol[1]
Appearance	White crystalline powder Colourless gas when burned
Density	1.04 g/cm3
Melting point	93°C, (366.15 K), (199.4 °F)
Boiling point	310 °C, (583.15 K), (590 °F)[3]
Vapor pressure	(mm Hg) 3.4 × 10−5 at 20 °C
Hazards
MSDS	External MSDS
NFPA 704	1 2 0
Related compounds
Related compounds	SDBS
Supplementary data page
Structure and properties	n, εr, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

2-chlorobenzalmalononitrile (also called o-chlorobenzylidene malononitrile) (chemical formula: C₁₀H₅ClN₂), a cyanocarbon, is the defining component of a "tear gas" commonly referred to as CS gas, which is used as a riot control agent. "CS gas" is actually an aerosol of a volatile solvent (a substance that dissolves other active substances and that easily evaporates with it) and 2-chlorobenzalmalononitrile, which is a solid compound at room temperature. CS gas is generally accepted as being non-lethal. It was discovered by two Americans, Ben Corson and Roger Stoughton, at Middlebury College in 1928, and the chemical's name is derived from the first letters of the scientists' surnames.^[4][5]

CS was developed and tested secretly at Porton Down in Wiltshire, England, in the 1950s and 1960s. CS was used first on animals, then subsequently on British Army servicemen volunteers. Notably, CS has a limited effect on animals due to "under-developed tear-ducts and protection by fur".^[6]

Production[link]

CS is synthesized by the reaction of 2-chlorobenzaldehyde and malononitrile via the Knoevenagel condensation:

ClC₆H₄CHO + H₂C(CN)₂ → ClC₆H₄CHC(CN)₂ + H₂O

The reaction is catalysed with weak base like piperidine or pyridine. The production method has not changed since the substance was discovered by Corson and Stoughton.^[7] Other bases, solvent free methods and microwave promotion have been suggested to improve the production of the substance.^[8]

The physiological properties had been discovered already by the chemists first synthesising the compound in 1928: "Physiological Properties. Certain of these dinitriles have the effect of sneeze and tear gases. They are harmless when wet but to handle the dry powder is disastrous."^[7]

Use as an aerosol[link]

As 2-chlorobenzalmalononitrile is a solid at room temperature, not a gas, a variety of techniques have been used to make this solid usable as an aerosol:

• Melted and sprayed in the molten form.
• Dissolved in organic solvent.
• CS₂ dry powder (CS₂ is a siliconized, micro-pulverized form of CS).
• CS from thermal grenades by generation of hot gases.^[1]

In the Waco Siege, CS was dissolved in the organic solvent dichloromethane (also known as methylene chloride). The solution was dispersed as an aerosol via explosive force and when the highly volatile dichloromethane evaporated, CS crystals precipitated and formed a fine dispersion in the air.^[1]

Effects[link]

Many types of tear gas and other riot control agents have been produced with effects ranging from mild tearing of the eyes to immediate vomiting and prostration. CN and CS are the most widely used and known, but around 15 different types of tear gas have been developed worldwide e.g. adamsite or bromoacetone, CNB, and CNC. CS has become the most popular due to its strong effect and lack of toxicity in comparison with other similar chemical agents. The effect of CS on a person will depend on whether it is packaged as a solution or used as an aerosol. The size of solution droplets and the size of the CS particulates after evaporation are factors determining its effect on the human body.^[9]

The chemical reacts with moisture on the skin and in the eyes, causing a burning sensation and the immediate forceful and uncontrollable shutting of the eyes. Effects usually include tears streaming from the eyes, profuse coughing, exceptional nasal discharge that is full of mucus, burning in the eyes, eyelids, nose and throat areas, disorientation, dizziness and restricted breathing. It will also burn the skin where sweaty and or sunburned. In highly concentrated doses it can also induce severe coughing and vomiting. Almost all of the immediate effects wear off within an hour (such as exceptional nasal discharge and profuse coughing), although the feeling of burning and highly irritated skin may persist for hours. Affected clothing will need to be washed several times or thrown away.

Toxicity[link]

Bogside Artists' mural of a boy running from CS gas in Derry.

Although described as a non-lethal weapon for crowd control, many studies have raised doubts about this classification. As well as creating severe pulmonary damage, CS can also significantly damage the heart and liver.^[10]

On September 28, 2000, Prof. Dr. Uwe Heinrich released a study commissioned by John C. Danforth, of the United States Office of Special Counsel, to investigate the use of CS by the FBI at the Branch Davidians' Mount Carmel compound. He concluded that the lethality of CS used would have been determined mainly by two factors: whether gas masks were used and whether the occupants were trapped in a room. He suggests that if no gas masks were used and the occupants were trapped, then, "...there is a distinct possibility that this kind of CS exposure can significantly contribute to or even cause lethal effects."^[1]

Many reports have associated CS exposure with miscarriages.^[10] This is consistent with its reported clastogenic effect (abnormal chromosome change) on mammalian cells.

When CS is metabolized, cyanide can be detected in human tissue.^[10] According to the United States Army Center for Health Promotion and Preventive Medicine, CS emits "very toxic fumes" when heated to decomposition, and at specified concentrations CS gas is an immediate danger to life and health. They also state that those exposed to CS gas should seek medical attention immediately.^[2]

In Israel, CS gas was reported to be the cause of death of Jawaher Abu Rahmah on December 31, 2010,^[11] although the Israel Defence Forces have questioned the veracity of the report. In Egypt, CS gas was reported to be the cause of death of several protesters in Mohamed Mahmoud street near Tahrir square on November 2011 protests.

It has been noted that the solvent MiBK is itself harmful, and can cause inflammation, dermatitis, burns to the skin and liver damage.^[12]

Decontamination[link]

CS contamination can be removed by washing with an alkaline solution of water and 5% sodium bisulfite.^[6][13]

Use[link]

RWGŁ-3 Polish tear gas grenade launcher.

CS was used to flush the Viet Cong from their tunnels in Vietnam.

CS is used in spray form by many police forces as a temporary incapacitant and to subdue attackers or persons who are violently aggressive. Officers that are trained in the use and application of CS spray are routinely exposed to it as part of their training.

Recently, blank pistol cartridges carrying CS in powder form have been released to public. These, when fired in relatively close ranges, fully expose the target to the effects of CS, and are employed as a potent defensive weapon in regions where blank firing pistols are legally permitted for such use.

Although predominantly used by police it has also been used in criminal attacks in various countries.^{[14][15][16][17]}

Use of CS in war is prohibited under the terms of the 1997 Chemical Weapons Convention, signed by most nations in 1993 with all but five other nations signing between the years of 1994 through 1997. The reasoning behind the prohibition is pragmatic: use of CS by one combatant could easily trigger retaliation with much more toxic chemical weapons such as nerve agents. Only five nations have not signed the Chemical Weapons Convention and are therefore unhindered by restrictions on the use of CS gas: Angola, Egypt, North Korea, Somalia, and Syria.^[18]

Domestic police use of CS is legal in many countries, however, as the Chemical Weapons Convention prohibits only military use.

Bahrain[link]

Bahrain riot police use tear gas on protesters in Manama during 2011-2012 Bahraini uprising

CS gas has been used extensively by Bahrain's police since the start of the 2011 Bahraini Uprising.^[19](p260) The Bahrain Independent Commission of Inquiry concluded that Bahrain's police used a disproportionate amount of CS gas when dispersing protests, and that in a number of situations, police fired CS gas into private homes in an "unnecessary and indiscriminate" manner.^[19](p277) In one particular incident witnessed by Commission investigators, police fired "at least four tear gas canisters (each containing six projectiles) ... from a short range into the kitchen and living room of a home."^[19](p261)

According to opposition activists and families of the deceased, ten individuals have died as a result of CS gas between 25 March 2011 and 17 December 2011.^{[20][21][22][23][24][25][26][27][28][29]} One allegedly died from the impact of the CS gas canister^[25], and the remainder are said to have died from the effects of inhaling the gas. The Bahrain Independent Commission of Inquiry received information that a further three deaths may have been attributable to the use of CS gas.^{[19](pp239-40,253)} Of these three, one allegedly died from the impact of the canister, and two from the effects of inhaling the gas.

Egypt[link]

CS was widely used by Egypt's Police/Military Forces in November 2011.^{[citation needed]}

Canada[link]

Quebec[link]

Since 2008 the SPVM police force in Montreal has been increasingly using CS Gas for crowd control as a "last resort". On Montreal’s riot squad, each officer is equipped with an MK-9 aerosol projector, which sprays the irritant at a distance of up to six feet. ^[30]

Recently questions have been raised by the apparent lack of use of force training for Montreal riot squad officers given a string of incidents where protesters have been seriously injured by being fired upon at point-blank range by CS gas ^[31] Youtube Video of March 8 2012 incident

Cyprus[link]

CS was first tested in the field by the British army in Cyprus in 1958. At this time it was known by the code name T792.^[32]

Iraq[link]

Iraq successfully developed CS during the 1970s and during the 1980s produced tons of the substance firstly at Salman Pak and later at al-Muthanna.^[33] Then-Iraqi leader Saddam Hussein ordered troops to use nerve agents against Iraqi Kurds in his own country and against Iran during the Iran–Iraq War. It is believed that Iraqi forces used multiple chemical agents during the attack, including mustard gas and the nerve agents sarin, soman, tabun and VX;^[34] some sources have also pointed to the blood agent hydrogen cyanide.

Blackwater Worldwide, acting as an agent of the United States, deployed CS in the Iraq War from a helicopter hovering over a checkpoint in the Green Zone in Bagdhad.^[35]

Israel[link]

Israel Police forces spray CS gas at riot control situations. It is widely used at demonstrations within the Palestinian Territories and at the Israeli West Bank barrier.^[36][37]

Philippines[link]

CS tear gas was used in suppression of the mutiny in Makati that was led by Sen. Antonio Trillanes. The tear gas was fired in the building and all the people in the building including reporters were affected.^{[citation needed]}

Sri Lanka[link]

The LTTE, also known as Tamil Tigers of Sri Lanka, an insurgent group in Sri Lanka used CS gas against government forces that were on an offensive to flush and defeat these insurgents during September 2008.^[38] Its use hindered the army's progress but ultimately proved ineffective in preventing the army from overrunning LTTE positions.

This is one of the first few cases of insurgents using CS gas as an insurgent weapon.

United Kingdom[link]

Northern Ireland[link]

A mural in Derry, Northern Ireland of a young boy in a gas mask holding a petrol bomb during the Battle of the Bogside, August 1969.

CS gas was used extensively in the Bogside area of Derry, Northern Ireland during the "Battle of the Bogside", a two-day riot in August, 1969. A total of 1,091 canisters containing 12.5g of CS each, and 14 canisters containing 50g of CS each, were released in the densely populated residential area.^[39] On 30 August the Himsworth Inquiry was set up to investigate the medical effects of its use in Derry. Its conclusions, viewed in the political context of the time, still pointed towards the necessity of further testing of CS gas before being used as a riot control agent. During the rioting in Belfast, the following year, known as the Falls Curfew, the Army fired up to 1,600 canisters into the densely populated Falls Road area. It was also used in Lenadoon on 9 July 1972 on the breakdown of the IRA ceasefire. Not long after, the British Army and RUC ceased using CS in Northern Ireland. Up to this point, it had been used in crowd control scenarios in Derry and Belfast.

Great Britain[link]

The first use of CS gas on the UK mainland that was not part of military training was carried out in 1944 during a hostage siege at a North London address. Soldiers were asked to throw CS grenades through the skylight in hope of bringing the incident to a speedy conclusion, however, the hostage-taker had brought his civilian-issue gas mask with him, negating the effect.^{[citation needed]}

The siege of Trough Gate, in Oldham, during 1973 was the second non-military use of CS gas on UK Mainland. It was applied to the rear of a van where the chief suspect was hiding. The suspect committed suicide with the handgun he was armed with.

The first use of CS tear gas to quell rioting in mainland Britain was in the Toxteth area of Liverpool in 1981.^[40]

CS gas incapacitant sprays were first introduced into the British police in 1995, to assist them in dealing with violent incidents.^[41] The CS is in the form of a hand-held aerosol canister, with the solution being 5% CS, with methyl isobutyl ketone as the solvent, which is propelled by pressurized nitrogen. The liquid stream is directed where the user points the canister, being accurate up to 4 metres. All forces dictate that for an officer to be authorised to carry CS, they have to have completed a training course in the spray's use. Under UK firearm law CS and other incapacitant sprays are classed as prohibited weapons, making it unlawful for a member of the public to possess such an item. In recent years, some forces have stopped using CS, in favour of the new PAVA spray.^[42]

A six month trial by sixteen police forces in England began on the 1 March 1996. Only two weeks later, on 16 March 1996, a Gambian asylum seeker, Ibrahima Sey was taken to Ilford Police Station in east London. Whilst incapacitating the man, police sprayed him with CS and held him on the ground for over 15 minutes, and he subsequently died. Although a verdict of unlawful killing was given by the jury at the end of the inquest into his death, no charges were brought against any member of the police force.^[43]

The police forces that do use the PIS in the UK require that the personnel undergoing training should themselves be sprayed with a 3% dissolved CS, during self-defense training, in order for them to be able to be authorized to carry it as personal protection equipment. They are also trained in helping the incapacitated person recover quickly once successfully restrained. Most forces currently issue CS spray to its officers, but there has been a recent move for a few forces to issue PAVA Spray (pelargonic acid vanillylamide aka nonivamide).

The CS spray used by UK police is generally more concentrated than spray used by American police forces depending on the particular city/state (e.g. Campus Police, Keyser, West Virginia.^[44]

In 1999 the UK mental health charity MIND called for a suspension in its use until it is fully tested and there is proof that CS is safe.^[45]

In February 2006, there were calls to have CS spray banned in the UK after Dan Ford, from Wareham in Dorset, was permanently facially scarred after being sprayed in the face with a police CS canister. Mr Ford was subsequently advised by doctors to stay out of sunlight for at least 12 months. After the incident, his cousin, Donna Lewis, was quoted as saying, "To look at him, it was like looking at a melting man, with liquid oozing from his face."^[46] However, it has not yet been confirmed that Mr Ford's injury was a reaction to having been exposed to police CS spray, or whether an unrelated chemical exposure caused the injury. An investigation is ongoing.

In January 2011, CS was used by the Metropolitan Police at a UK Uncut protest in London.^[47][48]

The British Armed Forces use CS gas annually to test their CBRN equipment. During initial training they introduce recruits to CS gas by ordering them into a small enclosed space known as a Respirator Test Facility (RTF) and igniting chemical tablets to induce CS production. After recruits have carried out their CBRN drills, they must remove their respirators and inhale the CS to realise it effects and become confident their masks work.^{[not in citation given] [49][50]}

United States[link]

CS is used by many police forces within the United States. It was most famously used as one of a number of techniques by Federal Bureau of Investigation law enforcement officials in the 1993 Waco Siege.^[51]

Riot police in Pittsburgh, Pennsylvania in September, 2009 used CS gas and riot control techniques to disperse assemblies in the vicinity of the 2009 G-20 Pittsburgh summit.

In Berkeley, California during the Bloody Thursday events in People's Park on Wednesday, May 21, 1969, a midday memorial was held for student James Rector, a non-protester shot to death by police, at Sproul Plaza on the University campus. In his honor, several thousand people peacefully assembled to listen to speakers remembering his life. Without warning, National Guard troops surrounded Sproul Plaza, donned their gas masks, and pointed their bayonets inward, while helicopters dropped CS gas directly on the trapped crowd. No escape was possible, and the gas caused acute respiratory distress, disorientation, temporary blindness and vomiting. Many people, including children and the elderly, were injured during the ensuing panic. The gas was so intense that breezes carried it into Cowell Memorial Hospital, endangering patients, interrupting operations and incapacitating nurses. Students at nearby Jefferson and Franklin elementary schools were also affected.^[52][53]

Members of the United States armed forces are exposed to CS during initial training, and during training refresher courses or equipment maintenance exercises, using CS tablets that are melted on a hotplate. This is to demonstrate the importance of properly wearing a gas or protective mask, as the agent's presence quickly reveals an improper fit or seal of the mask's rubber gaskets against the face. Following exposure while wearing a mask, recruits are ordered to remove the masks and endure exposure in the room for one minute. These exercises also encourage confidence in the ability of the equipment to protect the wearer from such chemical attacks. Such an event is a requirement for graduation from United States Army Basic Training, Air Force Basic Military Training, Navy Basic Training, and Marine Corps recruit training.^[54] CS gas in the form of grenades is also used extensively in the United States Marine Corps in some service schools. CS gas is used during the final field exercise of the Scout Sniper Basic Course to simulate being compromised. In addition, it is used during the 25 km (16 mi) escape-and-evasion exercise ("Trail of Tears"), the last event before graduation from the course. It is also used during several events in the Marine Corps Basic Reconnaissance Course (BRC) including some rucksack runs and escape-and-evasion exercises. While students going through the course are given the opportunity to bring and wear a gas mask for the event, usually none are worn because once donned, gas masks could not be removed until the end of the exercise. This could last anywhere from 3–12 hours and would make running 25 km while wearing 125 lb (57 kg) of gear virtually impossible.

Vietnam[link]

It has been reported that thousands of tons of CS gas were used by the U.S. forces in Vietnam to bring Viet Cong into the open. It was also used by the North Vietnamese forces in some battles like Hue in 1968 or during the Easter Offensive in 1972.^[55]

Elsewhere[link]

Police fire tear gas at protesters in Quebec.

CS gas has been and is still routinely used by Greek riot police (MAT) in order to quell student and labor protests, as well as riots by hooligans. In some cases gas had expired for more than thirty years. The legality and safety of the use of CS by policemen has been challenged both by people within Greece and the European Union.^{[citation needed]}

CS was used to quell a protest in Lusaka, Zambia in July 1997 and the 1999 WTO riots in Seattle. Amnesty International reported that it had been manufactured by the UK company Pains-Wessex. Subsequently, Amnesty called for an export ban when the receiving regime is either not fully trained in the use of CS, or had shown usage "contrary to the manufacturer’s instructions".^[56]

In September 2000, the Guardian newspaper revealed how a UK company, HPP, used legal loopholes to export CS to a private security company in Rwanda, in breach of United Nations sanctions.^[57] The Guardian also reported that CS was used by the Hutu militia in Rwanda to flush Tutsis out of buildings before hacking them to death.

CS has been used by the government in South Africa; by Israel against Palestinians and Israelis; by the South Korean government in Seoul, and during the Balkan conflicts by Serbia. In Malta it was used by Police between 1981 and 1987 to the detriment of Nationalist Party Supporters.

CS tear gas was used at the G8 protests in Genoa, Italy^[58] and Quebec City, Canada^[59] during the FTAA anti-globalization demonstrations during the Quebec City Summit of the Americas.

The Malaysia Federal Reserve Unit has also been known to use CS tear gas against its citizens who rallied for clean and fair elections under what were called Bersih rallies in 2011 ^[60] and 2012. ^[61]

The Canadian, Norwegian and Australian Armies train their soldiers with CS gas in a manner similar to that of the USA, as it is a basic part of CBRN (Chemical, Biological, Radiological, Nuclear) training. Gas is released by burning tablets, usually in a building reserved for this purpose (a "gas hut"). In the training, the person enters the building unprotected, and must fit and clear the gas mask before leaving. Other drills such as drinking and under-mask decontamination are also practiced. Some Norwegian units are exposed to CS-gas while engaged in physical activity such as push-ups.

See also[link]

Pharmacy and Pharmacology portal

References[link]

External links[link]

• Gas Chromatography NIST
• U.S. Army Center for Health Promotion and Preventive Medicine General Facts About Tear Agent O-Chlorobenzylidene Malononitrile (CS) {pdf}
• Patten report recommendations 69 and 70 relating to public order equipment A Paper prepared by the Steering Group led by the Northern Ireland Office – April 2001
• Committees on toxicity, mutagenicity and carcinogenicity of chemicals in food, consumer products and the environment statement on 2-chlorobenzylidene malononitrile (CS) and CS spray, September 1999. (pdf)
• Journal of Non-lethal Combatives, January 2003 Noxious Tear-Gas Bomb Mightier in Peace than in War.
• "Crowd Control Technologies: An Assessment Of Crowd Control Technology Options For The European Union" – The Omega Foundation (pdf)
• Health and safety in policing University of Nottingham paper on CS use in the UK.
• Information and effects of CS and CN gas
• BBC 'wiki' site – entry on CS gas
• eMedicine Information on irritants: Cs, Cn, Cnc, Ca, Cr, Cnb, PS
• Carron P-N, Yersin B (2009). "Management of the effects of exposure to tear gas". BMJ 338 (7710): 1554–1558. DOI:10.1136/bmj.b2283. 

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Gas phase particles (atoms, molecules, or ions) move around freely in the absence of an applied electric field.

Gas is one of the three classical states of matter (the others being liquid and solid). Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point (see phase change), boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons are so energized that they leave their parent atoms from within the gas. A pure gas may be made up of individual atoms (e.g. a noble gas or atomic gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or compound molecules made from a variety of atoms (e.g. carbon dioxide). A gas mixture would contain a variety of pure gases much like the air. What distinguishes a gas from liquids and solids is the vast separation of the individual gas particles. This separation usually makes a colorless gas invisible to the human observer. The interaction of gas particles in the presence of electric and gravitational fields are considered negligible as indicated by the constant velocity vectors in the image.

The gaseous state of matter is found between the liquid and plasma states,^[1] the latter of which provides the upper temperature boundary for gases. Bounding the lower end of the temperature scale lie degenerative quantum gases^[2] which are gaining increased attention these days.^[3] High-density atomic gases super cooled to incredibly low temperatures are classified by their statistical behavior as either a Bose gas or a Fermi gas. For a comprehensive listing of these exotic states of matter see list of states of matter.

Etymology[link]

The word gas is a neologism first used by the early 17th century Flemish chemist J.B. Van Helmont. Van Helmont's word appears to have been simply a phonetic transcription of the Greek word Chaos – the g in Dutch being pronounced like the English ch – in which case Van Helmont was simply following the established alchemical usage first attested in the works of Paracelsus. According to Paracelsus's terminology, chaos meant something like "ultra-rarefied water".^[4]

Physical characteristics[link]

Drifting smoke particles provide clues to the movement of the surrounding gas.

As most gases are difficult to observe directly with our senses, they are described through the use of four physical properties or macroscopic characteristics: pressure, volume, number of particles (chemists group them by moles) and temperature. These four characteristics were repeatedly observed by scientists such as Robert Boyle, Jacques Charles, John Dalton, Joseph Gay-Lussac and Amedeo Avogadro for a variety of gases in various settings. Their detailed studies ultimately led to a mathematical relationship among these properties expressed by the ideal gas law (see simplified models section below).

Gas particles are widely separated from one another, and as such are not as strongly intermolecularly bonded to the same degree as liquids or solids. These intermolecular forces result from electrostatic interactions between each gas particle. Like charged areas of different gas particles repel, while oppositely charged regions of different gas particles attract one another; gases that contain permanently charged ions are known as plasmas. Gaseous compounds with polar covalent bonds contain permanent charge imbalances and so experience relatively strong intermolecular forces, although the molecule while the compound's net charge remains neutral. Transient, randomly-induced charges exist across non-polar covalent bonds of molecules and electrostatic interactions caused by them are referred to as Van der Waals forces. The interaction of these intermolecular forces varies within a substance which determines many of the physical properties unique to each gas.^[5][6] A quick comparison of boiling points for compounds formed by ionic and covalent bonds leads us to this conclusion.^[7] The drifting smoke particles in the image provides some insight into low pressure gas behavior.

Compared to the other states of matter, gases have an incredibly low density and viscosity. Pressure and temperature influence the particles within a certain volume. This variation in particle separation and speed is referred to as compressibility. This particle separation and size influences optical properties of gases as can be found in the following list of refractive indices. Finally, gas particles spread apart or diffuse in order to homogeneously distribute themselves throughout any container.

Macroscopic[link]

Shuttle imagery of re-entry phase.

When observing a gas, it is typical to specify a frame of reference or length scale. A larger length scale corresponds to a macroscopic or global point of view of the gas. This region (referred to as a volume) must be sufficient in size to contain a large sampling of gas particles. The resulting statistical analysis of this sample size produces the "average" behavior (i.e. velocity, temperature or pressure) of all the gas particles within the region. By way of contrast, a smaller length scale corresponds to a microscopic or particle point of view.

From this global vantage point, the gas characteristics measured are either in terms of the gas particles themselves (velocity, pressure, or temperature) or their surroundings (volume). By way of example, Robert Boyle studied pneumatic chemistry for a small portion of his career. One of his experiments related the macroscopic properties of pressure and volume of a gas. His experiment used a J-tube manometer which looks like a test tube in the shape of the letter J. Boyle trapped an inert gas in the closed end of the test tube with a column of mercury, thereby locking the number of particles and temperature. He observed that when the pressure was increased on the gas, by adding more mercury to the column, the trapped gas volume decreased. Mathematicians describe this situation as an inverse relationship. Furthermore, when Boyle multiplied the pressure and volume of each observation, the product (math) was always the same, a constant. This relationship held true for every gas that Boyle observed leading to the law, (PV=k), named to honor his work in this field of study.

There are many math tools to choose from when analyzing gas properties. As gases are subjected to extreme conditions, the math tools become a bit more complex, from the Euler equations (inviscid flow) to the Navier-Stokes equations^[8] that fully account for viscous effects. These equations are tailored to meet the unique conditions of the gas system in question. Boyle's lab equipment allowed the use of algebra to obtain his analytical results. His results were possible because he was studying gases in relatively low pressure situations where they behaved in an "ideal" manner. These ideal relationships enable safety calculations for a variety of flight conditions on the materials in use. The high technology equipment in use today was designed to help us safely explore the more exotic operating environments where the gases no longer behave in an "ideal" manner. This advanced math, to include statistics and multivariable calculus, makes possible the solution to such complex dynamic situations as space vehicle reentry. One such example might be the analysis of the image depicting space shuttle reentry to ensure the material properties under this loading condition are not exceeded. It is safe to say that in this flight regime, the gas is no longer behaving ideally.

Pressure[link]

Pressurized gases.

The symbol used to represent pressure in equations is "p" or "P" with SI units of pascals.

When describing a container of gas, the term pressure (or absolute pressure) refers to the average force the gas exerts on the surface area of the container. Within this volume, it is sometimes easier to visualize the gas particles moving in straight lines until they collide with the container (see diagram at top of the article). The force imparted by a gas particle into the container during this collision is the change in momentum of the particle. As a reminder from classical mechanics, momentum, by definition, is the product of mass and velocity.^[9] Notice that during a collision only the normal component of velocity changes. A particle traveling parallel to the wall never changes its momentum. So the average force on a surface must be the average change in linear momentum from all of these gas particle collisions. To be more precise, pressure is the sum of all the normal components of force exerted by the particles impacting the walls of the container divided by the surface area of the wall. The image "Pressurized gases" depicts gas pressure and temperature spikes used in the entertainment industry.

Temperature[link]

Air balloon shrinks after submerging into liquid nitrogen

The symbol used to represent temperature in equations is T with SI units of kelvins.

The speed of a gas particle is proportional to its absolute temperature. The volume of the balloon in the video shrinks when the trapped gas particles slow down with the addition of extremely cold nitrogen. The temperature of any physical system is related to the motions of the particles (molecules and atoms) which make up the [gas] system.^[10] In statistical mechanics, temperature is the measure of the average kinetic energy stored in a particle. The methods of storing this energy are dictated by the degrees of freedom of the particle itself (energy modes). Kinetic energy added (endothermic process) to gas particles by way of collisions produces linear, rotational, and vibrational motion as well. By contrast, a molecule in a solid can only increase its vibration modes with the addition of heat as the lattice crystal structure prevents both linear and rotational motions. These heated gas molecules have a greater speed range which constantly varies due to constant collisions with other particles. The speed range can be described by the Maxwell-Boltzmann distribution. Use of this distribution implies ideal gases near thermodynamic equilibrium for the system of particles being considered.

Specific volume[link]

Expanding gases link to changes in specific volume.

The symbol used to represent specific volume in equations is "v" with SI units of cubic meters per kilogram.

The symbol used to represent volume in equations is "V" with SI units of cubic meters.

When performing a thermodynamic analysis, it is typical to speak of intensive and extensive properties. Properties which depend on the amount of gas (either by mass or volume) are called extensive properties, while properties that do not depend on the amount of gas are called intensive properties. Specific volume is an example of an intensive property because it is the ratio of volume occupied by a unit of mass of a gas that is identical throughout a system at equilibrium.^[11] 1000 atoms of protactinium as a gas occupy the same space as any other 1000 atoms for any given temperature and pressure. This concept is easier to visualize for solids such as iron which are incompressible compared to gases. When the seat ejection is initiated in the rocket sled image the specific volume increases with the expanding gases, while mass is conserved. Since a gas fills any container in which it is placed, volume is an extensive property.

Density[link]

The symbol used to represent density in equations is ρ (pronounced rho) with SI units of kilograms per cubic meter. This term is the reciprocal of specific volume.

Since gas molecules can move freely within a container, their mass is normally characterized by density. Density is the mass per volume of a substance or simply, the inverse of specific volume. For gases, the density can vary over a wide range because the particles are free to move closer together when constrained by pressure or volume or both. This variation of density is referred to as compressibility. Like pressure and temperature, density is a state variable of a gas and the change in density during any process is governed by the laws of thermodynamics. For a static gas, the density is the same throughout the entire container. Density is therefore a scalar quantity; it is a simple physical quantity that has a magnitude but no direction associated with it. It can be shown by kinetic theory that the density is inversely proportional to the size of the container in which a fixed mass of gas is confined. In this case of a fixed mass, the density decreases as the volume increases.

Microscopic[link]

If one could observe a gas under a powerful microscope, one would see a collection of particles (molecules, atoms, ions, electrons, etc.) without any definite shape or volume that are in more or less random motion. These neutral gas particles only change direction when they collide with another particle or the sides of the container. By stipulating that these collisions are perfectly elastic, this substance is transformed from a real to an ideal gas. This particle or microscopic view of a gas is described by the Kinetic-molecular theory. All of the assumptions behind this theory can be found in the postulates section of Kinetic Theory.

Kinetic theory[link]

Kinetic theory provides insight into the macroscopic properties of gases by considering their molecular composition and motion. Starting with the definitions of momentum and kinetic energy,^[12] one can use the conservation of momentum and geometric relationships of a cube to relate macro system properties of temperature and pressure to the microscopic property of kinetic energy per molecule. The theory provides averaged values for these two properties.

The theory also explains how the gas system responds to change. For example, as a gas is heated from absolute zero, when it is (in theory) perfectly still, its internal energy (temperature) is increased. As a gas is heated, the particles speed up and its temperature rise. This results in greater numbers of collisions with the container sides each second due to the higher particle speeds associated with elevated temperatures. As the number of collisions (per unit time) increase on the surface area of the container, the pressure increases in a proportional manner.

Brownian motion[link]

Brownian motion is the mathematical model used to describe the random movement of particles suspended in a fluid. The gas particle animation, using pink and green particles, illustrates how this behavior results in the spreading out of gases (entropy). These events are also described by particle theory.

Since it is at the limit of (or beyond) current technology to observe individual gas particles (atoms or molecules), only theoretical calculations give suggestions as to how they move, but their motion is different from Brownian Motion. The reason is that Brownian Motion involves a smooth drag due to the frictional force of many gas molecules, punctuated by violent collisions of an individual (or several) gas molecule(s) with the particle. The particle (generally consisting of millions or billions of atoms) thus moves in a jagged course, yet not so jagged as would be expected if an individual gas molecule was examined.

Intermolecular forces[link]

When gases are compressed, intermolecular forces like those shown here start to play a more active role.

As discussed earlier, momentary attractions (or repulsions) between particles have an effect on gas dynamics. In physical chemistry, the name given to these intermolecular forces is van der Waals force. These forces play a key role in determining physical properties of a gas such as viscosity and flow rate (see physical characteristics section). Ignoring these forces in certain conditions (see Kinetic-molecular theory) allows a real gas to be treated like an ideal gas. This assumption allows the use of ideal gas laws which greatly simplifies the path to a solution.

Proper use of these gas relationships requires us to take one more look at the Kinetic-molecular theory (KMT). When these gas particles possess a magnetic charge or Intermolecular force they gradually influence one another as the spacing between them is reduced (the hydrogen bond model illustrates one example). In the absence of any charge, at some point when the spacing between gas particles is greatly reduced they can no longer avoid collisions between themselves at normal gas temperatures found in a lab. Another case for increased collisions among gas particles would include a fixed volume of gas, which upon heating would contain very fast particles. What this means to us is that these ideal equations provide reasonable results except for extremely high pressure [compressible] or high temperature [ionized] conditions. Notice that all of these excepted conditions allow energy transfer to take place within the gas system. The absence of these internal transfers is what is referred to as ideal conditions (perfect – or well behaved) in which the energy exchange occurs only at the boundaries of the system. Real gases experience some of these collisions and intermolecular forces. When these collisions are statistically negligible [incompressible], results from these ideal equations are still valid. At the other end of the spectrum, when the gas particles are compressed into close proximity they behave more like a liquid, and hence another connection to fluid dynamics.

Simplified models[link]

An equation of state (for gases) is a mathematical model used to roughly describe or predict the state properties of a gas. At present, there is no single equation of state that accurately predicts the properties of all gases under all conditions. Therefore, a number of much more accurate equations of state have been developed for gases in specific temperature and pressure ranges. The "gas models" that are most widely discussed are "perfect gas", "ideal gas" and "real gas". Each of these models has its own set of assumptions to facilitate the analysis of a given thermodynamic system.^[13] Each successive model expands the temperature range of coverage to which it applies. The image of first powered flight at Kitty Hawk, North Carolina illustrates one example on the successful application of these relationships in 1903. More recent examples include the 2009 maiden flights of the first solar powered aircraft, the Solar Impulse, and the first commercial airliner to be constructed primarily from composite materials, the Dreamliner.

First flight at Kitty Hawk, NC.

Ideal and perfect gas models[link]

The equation of state for an ideal or perfect gas is the ideal gas law and reads

Failed to parse (Missing texvc executable; please see math/README to configure.): PV=nRT,

where P is the pressure, V is the volume, n is amount of gas (in mol units), R is the universal gas constant, 8.314 J/(mol K), and T is the temperature. Written this way, it is sometimes called the "chemist's version", since it emphasizes the number of molecules n. It can also be written as

Failed to parse (Missing texvc executable; please see math/README to configure.): PV=\rho R_s T,

where Failed to parse (Missing texvc executable; please see math/README to configure.): R_s

is the specific gas constant for a particular gas, in units J/(kg K). This notation is the "gas dynamicist's" version, which is more practical in modeling of gas flows involving acceleration without chemical reactions.

The ideal gas law does not make an assumption about the specific heat of a gas. In the most general case, the specific heat is a function of both temperature and pressure. If the pressure-dependence is neglected (and possibly the temperature-dependence as well) in a particular application, sometimes the gas is said to be a perfect gas, although the exact assumptions may vary depending on the author and/or field of science.

For an ideal gas, the ideal gas law applies without restrictions on the specific heat. An ideal gas is a simplified "real gas" with the assumption that the compressibility factor Z is set to 1 meaning that this pneumatic ratio remains constant. A compressibility factor of one also requires the four state variables to follow the ideal gas law.

This approximation is more suitable for applications in engineering although simpler models can be used to produce a "ball-park" range as to where the real solution should lie. An example where the "ideal gas approximation" would be suitable would be inside a combustion chamber of a jet engine.^[14] It may also be useful to keep the elementary reactions and chemical dissociations for calculating emissions.

Real gas[link]

21 April 1990 eruption of Mount Redoubt, Alaska, illustrating real gases not in thermodynamic equilibrium.

Each one of the assumptions listed below adds to the complexity of the problem's solution. As the density of a gas increases with pressure rises, the intermolecular forces play a more substantial role in gas behavior which results in the ideal gas law no longer providing "reasonable" results. At the upper end of the engine temperature ranges (e.g. combustor sections – 1300 K), the complex fuel particles absorb internal energy by means of rotations and vibrations that cause their specific heats to vary from those of diatomic molecules and noble gases. At more than double that temperature, electronic excitation and dissociation of the gas particles begins to occur causing the pressure to adjust to a greater number of particles (transition from gas to plasma).^[15] Finally, all of the thermodynamic processes were presumed to describe uniform gases whose velocities varied according to a fixed distribution. Using a non-equilibrium situation implies the flow field must be characterized in some manner to enable a solution. One of the first attempts to expand the boundaries of the ideal gas law was to include coverage for different thermodynamic processes by adjusting the equation to read pVⁿ = constant and then varying the n through different values such as the specific heat ratio, γ.

Real gas effects include those adjustments made to account for a greater range of gas behavior:

• Compressibility effects (Z allowed to vary from 1.0)
• Variable heat capacity (specific heats vary with temperature)
• Van der Waals forces (related to compressibility, can substitute other equations of state)
• Non-equilibrium thermodynamic effects
• Issues with molecular dissociation and elementary reactions with variable composition.

For most applications, such a detailed analysis is excessive. Examples where "Real Gas effects" would have a significant impact would be on the Space Shuttle re-entry where extremely high temperatures and pressures are present or the gases produced during geological events as in the image of the 1990 eruption of Mount Redoubt.

Historical synthesis[link]

Boyle's law[link]

Boyle's equipment.

Boyle's Law was perhaps the first expression of an equation of state. In 1662 Robert Boyle performed a series of experiments employing a J-shaped glass tube, which was sealed on one end. Mercury was added to the tube, trapping a fixed quantity of air in the short, sealed end of the tube. Then the volume of gas was carefully measured as additional mercury was added to the tube. The pressure of the gas could be determined by the difference between the mercury level in the short end of the tube and that in the long, open end. Through these experiments, Boyle noted that the gas volume varied inversely with the pressure.^[16] The image of Boyle's Equipment shows some of the exotic tools used by Boyle during his study of gases.

• Boyle's Law – describes a gas in which the number of particles and Temperature are constant.
• PV = constant in this situation constant = nRT from the ideal gas law.

Law of volumes[link]

In 1787, the French physicist and balloon pioneer, Jacques Charles, found that oxygen, nitrogen, hydrogen, carbon dioxide, and air expand to the same extent over the same 80 kelvin interval.

In 1802, Joseph Louis Gay-Lussac published results of similar, though more extensive experiments, indicating a linear relationship between volume and temperature. Gay-Lussac credited Charle's earlier work by naming the law in his honor. In the absence of this linkage, Dalton could have been in contention for this honor for his previously published work on partial pressures.

• Law of Volumes – Both Charles and Gay-Lussac played a role in developing this relationship.^[17]
• V/T = constant – notice that constant = nR/P from the ideal gas law.

Avogadro's law[link]

Dalton's notation.

In 1811, Amedeo Avogadro verified that equal volumes of pure gases contain the same number of particles. His theory was not generally accepted until 1858 when another Italian chemist Stanislao Cannizzaro was able to explain non-ideal exceptions. For his work with gases a century prior, the number that bears his name Avogadro's constant represents the number of atoms found in 12 grams of elemental carbon-12 (6.022×10²³ mol⁻¹). This specific number of gas particles, at standard temperature and pressure (ideal gas law) occupies 22.40 liters, which is referred to as the molar volume.

• Avogadro's Law – describes a gas in a container in which the pressure and temperature are constant. The simplified form for the ideal gas law follows:
• V/n = constant – notice that constant = RT/P from the ideal gas law.

Dalton's law[link]

In 1801, John Dalton published the Law of Partial Pressures from his work with ideal gas law relationship: The pressure of a mixture of gases is equal to the sum of the pressures of all of the constituent gases alone. Mathematically, this can be represented for n species as:

Pressure_total = Pressure₁ + Pressure₂ + ... + Pressure_n

The image of Dalton's journal depicts symbology he used as shorthand to record the path he followed. Among his key journal observations upon mixing unreactive "elastic fluids" (gases) were the following.^[18]:

• Unlike liquids, heavier gases did not drift to the bottom upon mixing.
• Gas particle identity played no role in determining final pressure (they behaved as if their size was negligible).

Special topics[link]

Compressibility[link]

Compressibility factors for air.

Thermodynamicists use this factor (Z) to alter the ideal gas equation to account for compressibility effects of real gases. This factor represents the ratio of actual to ideal specific volumes. It is sometimes referred to as a "fudge-factor" or correction to expand the useful range of the ideal gas law for design purposes. Usually this Z value is very close to unity. The compressibility factor image illustrates how Z varies over a range of very cold temperatures.

Reynolds number[link]

In fluid mechanics, the Reynolds number is the ratio of inertial forces (v_sρ) to viscous forces (μ/L). It is one of the most important dimensionless numbers in fluid dynamics and is used, usually along with other dimensionless numbers, to provide a criterion for determining dynamic similitude. As such, the Reynolds number provides the link between modeling results (design) and the full-scale actual conditions. It can also be used to characterize the flow.

Viscosity[link]

Satellite view of weather pattern in vicinity of Robinson Crusoe Islands on 15 September 1999, shows a unique turbulent cloud pattern called a Kármán vortex street

Viscosity, a physical property, is a measure of how well adjacent molecules stick to one another. A solid can withstand a shearing force due to the strength of these sticky intermolecular forces. A fluid will continuously deform when subjected to a similar load. While a gas has a lower value of viscosity than a liquid, it is still an observable property. If gases had no viscosity, then they would not stick to the surface of a wing and form a boundary layer. A study of the delta wing in the Schlieren image reveals that the gas particles stick to one another (see Boundary layer section).

Turbulence[link]

Delta wing in wind tunnel. The shadows form as the indices of refraction change within the gas as it compresses on the leading edge of this wing.

In fluid dynamics, turbulence or turbulent flow is a flow regime characterized by chaotic, stochastic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time. The Satellite view of weather around Robinson Crusoe Islands illustrates just one example.

Boundary layer[link]

Particles will, in effect, "stick" to the surface of an object moving through it. This layer of particles is called the boundary layer. At the surface of the object, it is essentially static due to the friction of the surface. The object, with its boundary layer is effectively the new shape of the object that the rest of the molecules "see" as the object approaches. This boundary layer can separate from the surface, essentially creating a new surface and completely changing the flow path. The classical example of this is a stalling airfoil. The delta wing image clearly shows the boundary layer thickening as the gas flows from right to left along the leading edge.

Maximum entropy principle[link]

As the total number of degrees of freedom approaches infinity, the system will be found in the macrostate that corresponds to the highest multiplicity. In order to illustrate this principle, observe the skin temperature of a frozen metal bar. Using a thermal image of the skin temperature, note the temperature distribution on the surface. This initial observation of temperature represents a "microstate." At some future time, a second observation of the skin temperature produces a second microstate. By continuing this observation process, it is possible to produce a series of microstates that illustrate the thermal history of the bar's surface. Characterization of this historical series of microstates is possible by choosing the macrostate that successfully classifies them all into a single grouping.

Thermodynamic equilibrium[link]

When energy transfer ceases from a system, this condition is referred to as thermodynamic equilibrium. Usually this condition implies the system and surroundings are at the same temperature so that heat no longer transfers between them. It also implies that external forces are balanced (volume does not change), and all chemical reactions within the system are complete. The timeline varies for these events depending on the system in question. A container of ice allowed to melt at room temperature takes hours, while in semiconductors the heat transfer that occurs in the device transition from an on to off state could be on the order of a few nanoseconds.

See also[link]

Notes[link]

References[link]

• Anderson, John D. (1984). Fundamentals of Aerodynamics. McGraw-Hill Higher Education. ISBN 0-07-001656-9. 
• John, James (1984). Gas Dynamics. Allyn and Bacon. ISBN 0-205-08014-6. 
• McPherson, William and Henderson, William (1917). An Elementary study of chemistry. 

Further reading[link]

• Philip Hill and Carl Peterson. Mechanics and Thermodynamics of Propulsion: Second Edition Addison-Wesley, 1992. ISBN 0-201-14659-2
• National Aeronautics and Space Administration (NASA). Animated Gas Lab. Accessed February, 2008.
• Georgia State University. HyperPhysics. Accessed February, 2008.
• Antony Lewis WordWeb. Accessed February, 2008.
• Northwestern Michigan College The Gaseous State. Accessed February, 2008.

v t e States of matter Solid Liquid Gas / Vapor Plasma Low energy Bose–Einstein condensate · Fermionic condensate · Quantum Hall · Rydberg matter · Strange matter · Superfluid · Supersolid High energy Degenerate matter · QCD matter · Quark–gluon plasma  · Supercritical fluid Other states Colloid · Glass · Liquid crystal · Magnetically ordered (Antiferromagnet, Ferrimagnet, Ferromagnet) · String-net liquid · Superglass Transitions Boiling · Boiling point · Condensation · Critical line · Critical point · Crystallization · Deionization · Deposition · Evaporation · Flash evaporation · Freezing · Ionization · Lambda point · Melting · Melting point · Regelation · Saturated fluid · Sublimation · Supercooling · Triple point · Vaporization Quantities Enthalpy of fusion · Enthalpy of sublimation · Enthalpy of vaporization · Latent heat · Latent internal energy · Trouton's ratio · Volatility Concepts Binodal · Compressed fluid · Cooling curve · Equation of state · Leidenfrost effect · Mpemba effect · Order and disorder (physics) · Spinodal · Superconductivity · Superheated vapor · Superheating · Thermo-dielectric effect

vep:Gaz

Leonard Wood
Major General Leonard Wood in 1903
Born	(1860-10-09)October 9, 1860 Winchester, New Hampshire
Died	August 7, 1927(1927-08-07) (aged 66) Boston, Massachusetts
Place of burial	Arlington National Cemetery
Allegiance	United States of America
Service/branch	United States Army
Years of service	1885–1921
Rank	Lieutenant General
Commands held	1st United States Volunteer Cavalry Chief of Staff of the United States Army
Battles/wars	Apache Wars Spanish-American War Philippine-American War
Awards	Medal of Honor
Other work	Governor General of Cuba

Leonard Wood (October 9, 1860 – August 7, 1927) was a physician who served as the Chief of Staff of the United States Army, Military Governor of Cuba and Governor General of the Philippines. Early in his military career, he received the Medal of Honor. Wood also holds officer service #2 in the Regular Army (John Pershing holds officer service #1). He was complicit in the 1906 Moro Crater massacre.

Biography[link]

Early life and career[link]

Born in Winchester, New Hampshire, he attended Pierce Academy in Middleborough, Massachusetts and Harvard Medical School, earning an M.D. degree in 1884 as an intern at Boston City Hospital.

He took a position as an Army contract physician in 1885, and was stationed at Fort Huachuca, Arizona. Wood participated in the last campaign against Geronimo in 1886, and was awarded the Medal of Honor, in 1898, for carrying dispatches 100 miles through hostile territory and for commanding an infantry detachment whose officers had been lost. He received the rank of captain in 1891.

While stationed at Fort McPherson in Atlanta, in 1893, Wood enrolled in graduate school at Georgia Tech, then known as the Georgia School of Technology, and became the school's second football coach and, as a player, its team captain. Wood led the team to its first ever football victory, 28 to 6, over the University of Georgia.^[1]

Spanish-American War[link]

Wood was personal physician to Presidents Grover Cleveland and William McKinley through 1898. It was during this period he developed a friendship with Theodore Roosevelt, then Assistant Secretary of the Navy. At the outbreak of the Spanish-American War, Wood, with Roosevelt, organized the 1st Volunteer Cavalry regiment, popularly known as the Rough Riders. Wood commanded the regiment in a successful engagement known as the Battle of Las Guasimas. When the brigade commander, Samuel B. M. Young, became ill, Wood received a field promotion to brigadier general of volunteers and assumed command of the 2nd Brigade, Cavalry Division, V Corps (which included the Rough Riders) and led the brigade to a famous victory at Kettle Hill and San Juan Heights.

Staff of the 1st US Volunteer Regiment, the "Rough Riders" in Tampa—Col Wood is 2nd from right with Lt Col Roosevelt far right.

After San Juan, Wood led the 2nd Cavalry Brigade for the rest of the war; he stayed in Cuba after the war and was appointed the Military Governor of Santiago in 1898, and of Cuba from 1899–1902. In that capacity, he relied on his medical experience to institute improvements to the medical and sanitary conditions in Cuba. He introduced numerous reforms similar to those of the Progressive Movement in the U.S.^[2] He was promoted to brigadier general of regulars shortly before moving to his next assignment.

Philippine-American War[link]

In 1902, he proceeded to the Philippines, where he commanded the Philippines Division and later became commander of the Department of the East. He was promoted to major general in 1903, and served as governor of Moro province from 1903–1906, a stronghold of Muslim rebellion. He received criticism for his handling of the battle at Bud Dajo where six hundred Moros were casualties, including women and children who were killed by long-distance artillery fire while they accompanied the Moro soldiers.^[3]

Army Chief of Staff[link]

Wood had known Theodore Roosevelt well before the Spanish-American War. Wood was named Army Chief of Staff in 1910 by President Taft, whom he had met while both were in the Philippines; he remains the only medical officer to have ever held that position. As Chief of Staff, Wood implemented several programs, among which were the forerunner of the Reserve Officer Training Corps (ROTC) program, and the Preparedness Movement, a campaign for universal military training and wartime conscription. The Preparedness Movement plan was scrapped in favor of the Selective Service System, shortly before World War I. He developed the Mobile Army, thus laying the groundwork for American success in World War I.

World War I[link]

Maj. Gen. Leonard Wood in later years

In 1914, Wood was replaced as Chief of Staff by William Wotherspoon. Wood was a strong advocate of the Preparedness Movement, led by Republicans, which alienated him from President Wilson. With the US entry into World War I, Wood was recommended by Republicans, in particular Henry Cabot Lodge, to be the U.S. field commander; however, War Secretary Newton Baker instead appointed John J. Pershing, amid much controversy. During the war, Wood was, instead, put in charge of the training of the 10th and 89th Infantry Divisions, both at Camp Funston. In 1915, he published The Military Obligation of Citizenship, and in 1916. Wood became the 14th American officer to hold the permanent rank of lieutenant-general. The permanent rank of lieutenant-general had last been awarded upon retirement to General Winfield Scott.

Republican politics[link]

Wood was an unsuccessful candidate for the Republican presidential nomination in the election of 1920. He was urged into running by the family and supporters of his old friend Theodore Roosevelt, who had himself been considering another campaign before his illness and death in 1919. He won the New Hampshire primary that year, but lost at the convention. Among the reasons why he did not become the candidate were rivals for the nomination, his obvious political inexperience, and the strong support he gave for the anti-Communist strategy of Democratic Attorney General A. Mitchell Palmer to defeat radical subversion. After the major candidates deadlocked, the nomination went to Warren G. Harding.

Philippines[link]

He retired from the Army in 1921, and was made Governor General of the Philippines, in which capacity he served from 1921 to 1927.^[4]

Wood died in Boston, Massachusetts after undergoing surgery for a recurrent brain tumor. He had initially been diagnosed in 1910 with a benign meningioma brought on by exposure to experimental weapons refuse.^{[citation needed]} This was resected by Harvey Cushing at that time, and Wood made a full recovery until the tumor later recurred. The successful removal of Wood's brain tumor represented an important milestone, indicating to the public the advances that had been made in the nascent field of neurosurgery, and extending Wood's life by almost two decades.^[5]

He is buried in Arlington National Cemetery.^[6][7] His brain is held at the Yale University School of Medicine as part of an historic collection of Harvey Cushing's patients' preserved brains.

Legacy[link]

Wood's actual field jacket from the Spanish American War seen in above photo—on display at the National Museum of American History

Camp Leonard Wood in Missouri, now Fort Leonard Wood, home of the United States Army Combat Engineer School, Chemical School, and Military Police School, and USAF 364 TRS Det 1, were named in his honor, as was the USS Leonard Wood (APA-12).

Leonard Wood Road in Baguio City, Philippines was named in his honor. A Public Elementary School in Barangay Jagobiao, Mandaue City, Philippines (inside Eversley Childs Sanitarium compound) was also named after him.

Ft. Leonard Wood is also a major TRADOC post for Basic Combat Training (BCT), home of the 10th Infantry Regiment.

Wood Street corner Gov. Lim Avenue in Zamboanga City, Philippines was also named in his nobility.

He is portrayed favorably in the 1997 miniseries Rough Riders by actor and former United States Marine Dale Dye.

Leonard Wood was portrayed in a less favorable light by Mark Twain and others for his part in leading the Moro Crater massacre in 1906.

A plaque in Wood's memory is found in Harvard University's Memorial Church.

On March 11, 2012, in an interview on the television program Fox News Sunday, presidential candidate Newt Gingrich said of his opponent Mitt Romney, "The fact is that Romney is probably the weakest Republican frontrunner since Leonard Wood in 1920, and Wood ultimately lost on the 10th ballot."^[8]

Medal of Honor citation[link]

Medal of Honor

Voluntarily carried dispatches through a region inhabited by hostile Indians, making a journey of 70 miles in one night and walking 30 miles the next day. Also for several weeks, while in close pursuit of Geronimo's band and constantly expecting an encounter, commanded a detachment of Infantry, which was then without an officer, and to the command of which he was assigned upon his own request.

See also[link]

	Biography portal
	United States Army portal
	World War I portal