Saturday, February 29, 2020

Alkali

Page semi-protected

Alkali

From Wikipedia, the free encyclopedia
Jump to navigation Jump to search
For other uses, see Alkali (disambiguation).
Not to be confused with Alkalinity.
"Alkaline" redirects here. For the power cell, see Alkaline battery. For the Jamaican dancehall musician, see Alkaline (musician).

In chemistry, an alkali (/ˈælkəlaɪ/; from Arabic: al-qaly "ashes of the saltwort") is a basic, ionic salt of an alkali metal or alkaline earth metal chemical element. An alkali also can be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. The adjective alkaline is commonly, and alkalescent less often, used in English as a synonym for basic, especially for bases soluble in water. This broad use of the term is likely to have come about because alkalis were the first bases known to obey the Arrhenius definition of a base, and they are still among the most common bases.

Etymology

The word "alkali" is derived from Arabic al qalīy (or alkali),[1] meaning the calcined ashes (see calcination), referring to the original source of alkaline substances. A water-extract of burned plant ashes, called potash and composed mostly of potassium carbonate, was mildly basic. After heating this substance with calcium hydroxide (slaked lime), a far more strongly basic substance known as caustic potash (potassium hydroxide) was produced. Caustic potash was traditionally used in conjunction with animal fats to produce soft soaps, one of the caustic processes that rendered soaps from fats in the process of saponification, one known since antiquity. Plant potash lent the name to the element potassium, which was first derived from caustic potash, and also gave potassium its chemical symbol K (from the German name Kalium), which ultimately derived from alkali.

Common properties of alkalis and bases

Alkalis are all Arrhenius bases, ones which form hydroxide ions (OH−) when dissolved in water. Common properties of alkaline aqueous solutions include:

  • Moderately concentrated solutions (over 10−3 M) have a pH of 7.1 or greater. This means that they will turn phenolphthalein from colorless to pink.
  • Concentrated solutions are caustic (causing chemical burns).
  • Alkaline solutions are slippery or soapy to the touch, due to the saponification of the fatty substances on the surface of the skin.
  • Alkalis are normally water-soluble, although some like barium carbonate are only soluble when reacting with an acidic aqueous solution.

Difference between alkali and base

The terms "base" and "alkali" are often used interchangeably, particularly outside the context of chemistry and chemical engineering.

There are various more specific definitions for the concept of an alkali. Alkalis are usually defined as a subset of the bases. One of two subsets is commonly chosen.

  • A basic salt of an alkali metal or alkaline earth metal[2] (This includes Mg(OH)2 but excludes NH3.)
  • Any base that is soluble in water and forms hydroxide ions[3][4] or the solution of a base in water.[5] (This includes Mg(OH)2 and NH3.)

The second subset of bases is also called an "Arrhenius base".

Alkali salts

Alkali salts are soluble hydroxides of alkali metals and alkaline earth metals, of which common examples are:

  • Sodium hydroxide (NaOH) – often called "caustic soda"
  • Potassium hydroxide (KOH) – commonly called "caustic potash"
  • Lye – generic term for either of two previous salts or their mixture
  • Calcium hydroxide (Ca(OH)2) – saturated solution known as "limewater"
  • Magnesium hydroxide (Mg(OH)2) – an atypical alkali since it has low solubility in water (although the dissolved portion is considered a strong base due to complete dissociation of its ions)

Alkaline soil

Main article: Alkali soil

Soils with pH values that are higher than 7.3 are usually defined as being alkaline. These soils can occur naturally, due to the presence of alkali salts. Although many plants do prefer slightly basic soil (including vegetables like cabbage and fodder like buffalo grass), most plants prefer a mildly acidic soil (with pHs between 6.0 and 6.8), and alkaline soils can cause problems.[1]

Alkali lakes

In alkali lakes (also called soda lakes), evaporation concentrates the naturally occurring carbonate salts, giving rise to an alkalic and often saline lake.

Examples of alkali lakes:

See also

References

  1. ^ a b Chambers's encyclopaedia: a dictionary of universal knowledge, Volume 1. J.B. Lippincott & Co. 1888. p. 148.
  2. ^ Alkali | Define Alkali at Dictionary.com. Dictionary.reference.com. Retrieved on 2012-04-18.
  3. ^ alkali – definition of alkali by the Free Online Dictionary, Thesaurus and Encyclopedia. Thefreedictionary.com. Retrieved on 2012-04-18.
  4. ^ Chung, L.H.M. (1997) "Characteristics of Alkali", pp. 363–365 in Integrated Chemistry Today. ISBN 9789623722520
  5. ^ Acids, Bases and Salts. KryssTal. Retrieved on 2012-04-18.
  6. ^ Davis, Jim and Milligan, Mark (2011). Why is Bear Lake so blue? Archived 2015-07-02 at the Wayback Machine Public Information Series 96. Utah Geological Survey, Department of Natural Resources
Retrieved from "https://en.wikipedia.org/w/index.php?title=Alkali&oldid=935036252"
Posted by at No comments:

Agner Krarup Erlang

Agner Krarup Erlang

From Wikipedia, the free encyclopedia
Jump to navigation Jump to search
Agner Krarup Erlang
Erlang.jpg
Born1 January 1878 (1878-01)
Lønborg, Denmark
Died3 February 1929 (1929-02-04) (aged 51)
Copenhagen, Denmark
OccupationMathematician, statistician, and engineer

Agner Krarup Erlang (1 January 1878 – 3 February 1929) was a Danish mathematician, statistician and engineer, who invented the fields of traffic engineering[1] and queueing theory.[2]

By the time of his relatively early death at the age of 51, Erlang had created the field of telephone networks analysis. His early work in scrutinizing the use of local, exchange and trunk telephone line usage in a small community to understand the theoretical requirements of an efficient network led to the creation of the Erlang formula, which became a foundational element of modern telecommunication network studies.

Life[edit]

Erlang was born at Lønborg, near Tarm, in Jutland. He was the son of a schoolmaster, and a descendant of Thomas Fincke on his mother's side. At age 14, he passed the Preliminary Examination of the University of Copenhagen with distinction, after receiving dispensation to take it because he was younger than the usual minimum age. For the next two years he taught alongside his father.[1]:10-12

A distant relative provided free board and lodging, and Erlang prepared for and took the University of Copenhagen entrance examination in 1896, and passed with distinction. He won a scholarship to the University and majored in mathematics, and also studied astronomy, physics and chemistry. He graduated in 1901 with an MA and over the next 7 years taught at several schools.[1]:13 He maintained his interest in mathematics, and received an award for a paper that he submitted to the University of Copenhagen.[1]:14

He was a member of the Danish Mathematicians' Association (DMF) and through this met amateur mathematician Johan Jensen, the Chief Engineer of the Copenhagen Telephone Company (KTAS in Danish), an offshoot of the International Bell Telephone Company.[1]:14 Erlang worked for the CTC (KTAS) from 1908 for almost 20 years, until his death in Copenhagen after an abdominal operation.[1]:19

He was an associate of the British Institution of Electrical Engineers.[1]:18

Contributions[edit]

While working for the CTC, Erlang was presented with the classic problem of determining how many circuits were needed to provide an acceptable telephone service. His thinking went further by finding how many telephone operators were needed to handle a given volume of calls. Most telephone exchanges then used human operators and cord boards to switch telephone calls by means of jack plugs.[2]

Out of necessity, Erlang was a hands-on researcher. He would conduct measurements and was prepared to climb into street manholes to do so. [1]:17 He was also an expert in the history and calculation of the numerical tables of mathematical functions, particularly logarithms. He devised new calculation methods for certain forms of tables.[3]:109-110

He developed his theory of telephone traffic over several years. His significant publications include:

  • 1909 – "The Theory of Probabilities and Telephone Conversations", which proves that the Poisson distribution applies to random telephone traffic.[4][5][6]
  • 1917 – "Solution of some Problems in the Theory of Probabilities of Significance in Automatic Telephone Exchanges", which contains his classic formulae for call loss and waiting time.[7][8]
  • 1920 - "Telephone waiting times", which is Erlang's principal work on waiting times, assuming constant holding times.[9][10]

These and other notable papers were translated into English, French and German. His papers were prepared in a very brief style and can be difficult to understand without a background in the field. One researcher from Bell Telephone Laboratories is said to have learned Danish to study them.[1]:17

The British Post Office accepted his formula as the basis for calculating circuit facilities.[1]:17

In 1946, the CCITT named the international unit of telephone traffic "the Erlang".[11][1]:19-22 A statistical distribution and programming language listed below have also been named in his honour.

See also[edit]

References[edit]

  1. ^ a b c d e f g h i j k Brockmeyer, E.; Halstrøm, H. L. (1948), "The Life of A.K. Erlang" (PDF), in Brockmeyer, E.; Halstrøm, H. L.; Jensen, Arne (eds.), The Life and Works of A.K. Erlang, Transactions of the Danish Academy of Technical Sciences, 2, Akademiet for de Tekniske Videnskaber, pp. 9–22, archived from the original (PDF) on July 19, 2011
  2. ^ a b Achak, Matthew (2014-02-28), "Understanding Erlang and Queuing Theory", FCR, retrieved 2019-02-24
  3. ^ Brockmeyer, E. (1948), "A Survey of A. K. Erlang's Mathematical Works" (PDF), in Brockmeyer, E.; Halstrøm, H. L.; Jensen, Arne (eds.), The Life and Works of A.K. Erlang, Transactions of the Danish Academy of Technical Sciences, 2, Akademiet for de Tekniske Videnskaber, pp. 101–126, archived from the original (PDF) on July 19, 2011
  4. ^ Erlang, Agner K. (1909), "Sandsynlighedsregning og Telefonsamtaler" [Probability Calculation and Telephone Conversations], Nyt Tidsskrift for Matematik (in Danish), 20 (B): 33–39, JSTOR 24528622
  5. ^ Erlang, Agner K. (1925), "Calcul des probabilités et conversations téléphoniques" [Probability Calculation and Telephone Conversations], Revue générale de l'Electricité (in French), 18 (8): 305–309
  6. ^ Erlang, Agner K. (1948), "The Theory of Probabilities and Telephone Conversations" (PDF), in Brockmeyer, E.; Halstrøm, H. L.; Jensen, Arne (eds.), The Life and Works of A.K. Erlang, Transactions of the Danish Academy of Technical Sciences, 2, Akademiet for de Tekniske Videnskaber, pp. 131-137 (this English translation is based on the French original from 1925), archived from the original (PDF) on July 19, 2011
  7. ^ Erlang, Agner K. (1917), "Løsning af nogle Problemer fra Sandsynlighedsregningen af Betydning for de automatiske Telefoncentraler" [Solution of some Problems in the Theory of Probabilities of Significance in Automatic Telephone Exchanges], Elektroteknikeren (in Danish), 13: 5-13
  8. ^ Erlang, Agner K. (1948), "Solution of some Problems in the Theory of Probabilities of Significance in Automatic Telephone Exchanges" (PDF), in Brockmeyer, E.; Halstrøm, H. L.; Jensen, Arne (eds.), The Life and Works of A.K. Erlang, Transactions of the Danish Academy of Technical Sciences, 2, Akademiet for de Tekniske Videnskaber, pp. 138–155, archived from the original (PDF) on July 19, 2011
  9. ^ Erlang, Agner K. (1920), "Telefon-Ventetider. Et Stykke Sandsynlighedsregning" [Telephone Waiting Times. A Bit of Probability Calculation], Matematisk Tidsskrift B, 31: 25-42
  10. ^ Erlang, Agner K. (1948), "Telephone Waiting Times" (PDF), in Brockmeyer, E.; Halstrøm, H. L.; Jensen, Arne (eds.), The Life and Works of A.K. Erlang, Transactions of the Danish Academy of Technical Sciences, 2, Akademiet for de Tekniske Videnskaber, pp. 156–171, archived from the original (PDF) on July 19, 2011
  11. ^ "Traffic handled on a circuit or group of circuits", CCIF - XIVth Plenary Assembly, Montreux, 26 - 31 October: International Telephone Consultative Committee, 1946, pp. 60–62, hdl:11.1004/020.1000/4.237.43.en.1001CS1 maint: location (link)
Retrieved from "https://en.wikipedia.org/w/index.php?title=Agner_Krarup_Erlang&oldid=941829971"
Posted by at No comments:
Subscribe to: Posts (Atom)