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D LAYER

The D Layer is the lowest region of ionised gas in the ionosphere. It exists only during the hours of daylight, at an altitude of about 70 km.
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D'ARSONVAL GALVANOMETER

The D'Arsonval galvanometer is a galvanometer consisting of a large fixed magnet and a light coil that swings in the magnetic field.
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D/A CONVERTER

In audio engineering a D/A Converter is a device for the conversion of a digital data stream into analog signals. The digital word is buffered and then converted into an analog signal. After conversion, the analog signal is usually processed through a smoothing filter which removes the step transitions between the digital words.
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DAGUERREOTYPE

Daguerreotype was the earliest process of photographic reproduction, and was so called after its inventor Louis Daguerre. A copper plate, polished and silvered, was sensitised by exposure to iodine vapour, and so coated with a fine layer of silver iodide. It was then exposed in a camera, like modern photographic film, but with a longer exposure time. It was afterwards removed and treated with mercury vapour, the mercury attaching itself to those areas which had been most exposed to light and settling there in a density proportionate to the strength of the light.
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DAKIN'S SOLUTION

Dakin's Solution is a disinfectant solution containing sodium hydrochlorite, rendered neutral by the addition of boric acid as a buffer. The disinfectant action of the solution is very rapid, but it has the disadvantage of being unstable and does not keep for more than about a week.
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DALAPON

Dalapon is a low toxicity organochlorine herbicide and plant growth regulator based on sodium salt, used to control specific annual and perennial grasses, such as quackgrass, Bermuda grass, Johnson grass, cattails and rushes, chiefly in the sugar growing industry. It is also known as: basfapon B, dalapon sodium, 2-dichloropropionic acid, alpha-alpha-dichloropropionic acid, 2-dichlorpropionsaeure natrium, Dowpon, 2-DPA, gramevin, radapon, sodium dalapon, sodium 2,2-dichloropropionate and unipon.
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DAMASCUS-STEEL

Damascus-steel is a kind of steel originally made in Damascus and the East, formerly greatly valued in the making of swords for its hardness of edge and flexibility. It is a laminated metal of pure iron and steel of peculiar quality, carbon being present in excess of ordinary proportions, produced by careful heating, laborious forging, doubling, and twisting.
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DAMMAR GUM

Dammar Gum (Damar) is a naturally occurring gum obtained from coniferous trees that grow in the East Indies and Philippines. Dammar gum is soluble in turpentine and is employed in interior varnish and lacquers, such as crystal paper varnish.
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DAMP

In physics, damp refers to the diminishment of the amplitude of something, such as oscillations.
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DANIELL'S BATTERY

Daniell's Battery (named after the English physicist John Daniell) was a galvanic battery the cells of which were originally constructed in the following way. A tall cylindrical copper vessel was nearly filled with a saturated solution of copper sulphate. A rod of amalgamated zinc was enclosed in a skin or bladder, which was filled with dilute sulphuric acid, and was suspended in the copper cylinder. When the zinc rod was connected by a wire with the copper vessel, which itself formed one of the plates of the battery, the current passed, according to common phraseology, from the copper through the wire to the zinc. Instead of the bladder or skin porous earthenware pots were later employed to contain the dilute sulphuric acid in which the zinc was immersed. In improved modifications of Daniell's battery the most important change was that of substituting for the dilute sulphuric acid that surrounded the zinc, solution of zinc sulphate, and in this case the zinc was not amalgamated. By doing away with the sulphuric acid local waste of the zinc was to a great extent prevented, and the solution of sulphate of zinc was used instead of pure water on account of the very high resistance of water impregnated with salts.
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DANTOIN 685

Dantoin 685 is a preservative used in shampoos and deodorants. It contains formaldehyde and N-acetal and is highly toxic. It is also listed as DMDM hydantoin.
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DARBY STEAM-DIGGER

The Darby steam-digger was a light traction engine designed for ploughing fields. It was first exhibited at Carlisle in 1880, and could cultivate one acre an hour to a maximum depth of 14 inches.
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DARK ROOM

A dark room is a specially darkened studio used for photographic work. As much of the material used in photography is sensitive to light, many operations must be conducted in darkness.
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DARKNET

In computing, the term darknet refers to any closed, private network that operates on top of the more conventional internet protocols. The darkweb is a term used to describe data on the world wide web which is inaccessible to search engines, such as private data and data only accessible through private networks (darknets). One's online banking details are in the 'darkweb', they are protected by a password and as such are inaccessible by search engine spiders, but are not sinister.
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DARLINGTON PAIR

A Darlington Pair is an electronic circuit using two transistors with the collectors connected together and the emitter of the first directly coupled to the base of the second. This configuration gives very high gains equal to the gains of the two individual transistors multiplied together.
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DARWINISM

Darwinism is the views, especially regarding the origin and development of animals and plants, expressed in detail and advocated with much earnestness in the works of Charles Darwin.
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DAT CASSETTE

A DAT cassette is a high quality, special metal chrome cassette tape.
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DATA

Data is information, especially that stored in a computer.
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DATA PROTECTION

Data protection are safeguards relating to personal data in the UK, i.e. personal information about individuals that is stored on a computer. The principles of data protection, the responsibilities of data users, and the rights of data subjects are governed by the Data Protection Act (1984).
The principles of data protection include the following: (1) The information to be contained in personal data shall be obtained, and personal data shall be processed, fairly and lawfully. (2) Personal data shall be held only for specified and lawful purposes and shall not be used or disclosed in any manner incompatible with those purposes. (3) Personal data held for any purpose shall be relevant to that purpose. (4) Personal data shall be accurate and, where necessary, kept up to date. (5) Personal data held for any purpose shall not be kept longer than necessary for that purpose. (6) Appropriate security measures shall be taken against unauthorized access to, or alteration, disclosure, or destruction of personal data and against accidental loss or destruction of personal data.

Data users must register their activities with the Data Protection Registrar by means of a registration form obtained from a post office. This requires the data user to give: a description of the personal data it holds and the purposes for which the data is held; a description of the sources from which it intends or may wish to obtain the data or the information to be contained in the data; a description of any persons to whom it intends or may wish to disclose the data; the names or a description of any countries or territories outside the UK to which it intends or may wish directly or indirectly to transfer from data subjects for access to the data. A data user who fails to register is guilty of the offence of failing to register. An individual is entitled to be informed by any data user whether he holds personal data of which that individual is the subject. He is also entitled to obtain a printout from a registered data user of any personal data held by him and to demand that any inaccurate or misleading information is corrected or erased. If a court is satisfied on the application of a data subject that personal data held by a data user concerning him is inaccurate it may order the rectification or erasure of the data. Additionally it may order the rectification or erasure of any data held by the data user that contains an expression of opinion that appears to the court to be based on the inaccurate data.
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DATAEASE

DataEase is a package for users who hate to program but want to create custom database applications. It is menu-driven yet offers many powerful features available in other systems only through programming. You can set up a system complete with custom menus and help messages. Menus can have different levels of password protection, which adds security to the system. The package allows you to create a multiple-choice list for a particular field, thereby avoiding the need to design a cryptic coding system. It features financial and scientific functions as well as transaction processing. The report writer is based on the SQL query language. This can be difficult for the novice, although prompts help to compensate for this deficiency. Reports can be designed with data-entry screens, which let you specify different criteria for a report each time it is run. A Quick Report facility will do most of the design work, allowing users to add more advanced features. A library of report templates can be stored for future use.
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DATATALK

Datatalk is a menu driven communications package that has an underlying command language that allows the user to automate most operations, including file collection, transmission and printing. It can also provide access to a remote PC where any DOS applications can be executed, but with the display and keyboard entry occurring locally. In addition to dumb terminal operation,
Datatalk can emulate DEC VT52 and VT100, as well as Viewdata terminals. Unlike other programs on the market, the entire Viewdata character set can be viewed with any colour graphics or Hercules graphics board: no replacement ROM chips are needed. Datatalk can be used with modems that operate at speeds of up to 9600 baud. This package supports auto-dial and auto-answer modems and is packaged preconfigured for a wide variety of them. When emulating a Viewdata terminal, it will, if requested, capture screens for later viewing. It will also convert the graphics characters into normal text so that they can be loaded into other PC software. Up to 128 telephone numbers can be stored in the Datatalk telephone directory. The software will configure the serial port, select the correct terminal emulation, load pre-defined function keys, dial the number and perform automatic log-in. An optional file encryption module, Datacode, is available for users with sensitive data.
Datatalk emulates TTY, TVI 920, IBM 3101, ADDS A2, Lear Siegler ADM3A and ADM11, IBM 3101, Newbury 8089, Cifer, DEC VT52, Datatalk, Viewdata and VT100 terminals. It is best suited for accessing Viewdata services, like Prestel. Datatalk has some limitations, for example the VT100 emulation is not as sophisticated as some other products. In particular, it will not scroll horizontally to view all 132 columns on an 80 column screen. The text editor is restricted to 200 lines. When using this product to remotely configure another PC, it will only work with software that inputs and outputs using the BIOS services.
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DATURINE

Daturine is the poisonous alkaloid found in the thorn-apple.
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DAVYUM

Davyum (named after Sir Humphry Davy) was the name given to a supposed metal of the platinum group which Kern professed to have discovered, in 1877, in Russian platinum ore. Its existence as an element, however, was never established.
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DBASE III PLUS

Ashton-Tate's dBase III Plus became an industry standard relational database management system The product line, beginning with dBase II (formerly known as Vulcan), which was the first database manager for the personal computer, was built around a powerful, flexible programming language. Many third party vendors have chosen to support the dBase standard and there are a variety of add-on and work-alike products available. dBase III Plus includes The Assistant, a menu-driven program with some relational capabilities that leads you through the maze of dBase procedures using pull-down menus and context-sensitive help. The commands in The Assistant appear on the screen. The Applications Generator is a menu-driven dBase module that brings you through the process of creating a custom program and shows how to design screens, menus, and reports.
dBase III Plus includes a 'Data Catalog' to keep track of related files. When you enter '?' you get a list of all files currently available. The menu-driven query facility lets you define and save a filter criteria.
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DBASE IV

Ashton-Tate's dBase IV was a greatly enhanced version of dBase III Plus and provided more facilities for the power user to develop turnkey applications without the need to write code. The Control Center was an extension of The Assistant in dBase III Plus and was much more powerful. The Control Center let users open and close files, create views and reports, and run programs that provide the novice end-user with easier access to dBase files. Reports, forms, and queries produced through the Control Center generate dBase source code which can be edited. The Query By Example panel of the Control Center displays a visual representation of the data file. By specifying criteria within a view, you can select records, display fields, or combine data from several database files. Without leaving dBase IV, you can run DOS operations such as CHKDSK or DIR through the DOS window. dBase IV can save 47 indexes to a single file. Index files are automatically created with every database file. Each time you open a database file, the associated index file is automatically opened. This is much easier than opening data and index files separately as required in dBase III Plus. The new Application Generator writes all code necessary for incorporating forms, reports, and files into a turnkey application. The dBase/SQL command programming language lets you create, modify, or query databases using SQL commands. You can issue SQL commands from the dot prompt and include SQL procedures within dBase programs. This allows access to dBase files by mainframe and minicomputer users who are familiar with SQL. When dBase IV executes SQL commands, it first translates the code from SQL to actual dBase source code. This translation prevents users from accessing external SQL code. Enhancements to the programming language let you create two dimensional arrays, multi-child relationships, and data validation support. A transaction processing procedure creates a transaction log file of changes made to
se files. This helps avoid data loss due to power shortages, inadvertent reboots, and system failures.

When used with Ashton-Tate's Chart-Master, the dBase/ Chart-Master Bridge let users graph data files. The report and form generator are WYSIWYG, so it is easier to develop forms and reports. The screen painter displays memo fields through a window, and a pseudo compiler increases the speed of all commands issued at the dot prompt up to ten times faster than in dBase III Plus. Memo fields can be searched, copied to and from, and are available for program control. This lets you program
dBase IV to perform automatic queries on memo fields. Built-in printer drivers support bold, italics, underlining, superscript, and subscript printing.
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DBM

dBM is an identifier meaning 'decibels referred to one milliwatt,' the common reference point for power levels in telecommunications circuits.
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DBRIEF

dbrief by Solution Systems is a custom language editor used for writing dBase compatible code and provides an integrated environment in which to develop applications. dbrief is a custom version of brief. In order to run
dbrief you must have a copy of brief. dbrief is flexible and can be modified to fit programming needs. The program can be used to edit memo fields or program files in dBase.
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DC AMPLIFIERS

The first IC DC amplifier was the 709, introduced by Fairchild in the mid 1960s. The 709 by today's standard has many shortcomings, and a whole family of amplifiers has been produced. The commonest is the 741 which has been described as the Universal Component. A DC amplifier chip in its simplest form has just six connections. The positive supply, negative supply and the output are obvious. The amplifier has two inputs. These are known, respectively, as the non inverting and the inverting inputs. The amplifier amplifies the voltage between the two inputs. Let us assume, therefore, that the input is connected to 0V and an input signal applied to the +ve input. It will be found that the output moves in the same sense as the output. If we reverse the input connections, and connect the signal to the input, and the +ve input to 0V, the output will move in the opposite sense to the input. The terms 'inverting' and 'non inverting' thus refer to the sense of the inputs with respect to the resulting output. DC amplifiers are characterised by very high gains; 200,000 being typical for the common 741. Normally supplies of a 15V are used, so an input voltage of less than 1mV will cause the output to saturate. In practice, all DC amplifiers are invariably used with negative feedback which, in conjunction with high gains, gives very predictable results.
DC amplifiers are used in instrumentation, audio circuits, filter design and industrial control. By the early 1980s they had become a universal component.
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DDT

Ddt is an insecticide discovered in 1939 by Paul Muller.
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DEBUSSCOPE

The debusscope is an instrument somewhat similar to a kaleidoscope, useful for devising patterns for calico-printers. It was invented in France around 1860.
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DEC

DEC (Digital Equipment Corporation) are a company founded by Kenneth Olsen and Harlan Anderson, both formerly of the MIT's Lincoln Laboratories. DEC was formed to build transistorised digital circuit modules and went on to produce the world's first minicomputer, and to become the world's major producer of minicomputers.
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DECAGON

A decagon is a ten-sided polygon.
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DECAHYDRO-NAPHTHALENE

Decahydro-naphthalene is naphthalene which has been completely reduced by catalytic hydrogenation. It is a colourless liquid with a pleasant odour and the formulae C10H18 used as a solvent and cleaning-agent.
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DECALIN

Decalin was a commercial name for Decahydro-naphthalene.
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DECELERATION

Deceleration is the rate at which a moving body decreases in velocity.
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DECIBEL

The decibel is the unit of measurement of sound intensity. In electronics, the
decibel is a unit of measurement representing the logarithmic a ratio of two voltages, currents or power levels; used in telecommunications to express transmission loss or gain; defined as one-tenth of a Bel, hence the notation dB.
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DECLINATION

In astronomy, declination is the angular distance of a heavenly body north or south of the celestial equator (equinoctial), measured on a great circle passing through the pole and also through the body. If the body is north of the equator the declination is described as positive and if south negative. Parallels of declination are the circles parallel to the equator traversed by stars in their diurnal motion round the pole.
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DECLINOMETER

A declinometer (declination needle) is an instrument for registering the amount and variation of magnetic declination.
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DEFLECTION YOKE

In electronics, a deflection yoke is an assembly of one or more coils through which a controlled current is passed to produce a magnetic field for deflecting a beam of electrons, such as is used in a television with a Cathode-ray tube screen.
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DEGREE

In algebra, a degree is rank as determined by the power to which a quantity is to be raised.

In arithmetic, a degree is a group of three digits in numbers of more than three figures, which are often counted off by threes from the decimal point.
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DEHYDRATION

In chemistry, dehydration is the removal of water from a substance.
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DEKATRON

A dekatron is a gas-filled cold-cathode electron tube, having a central anode and ten effective cathodes, used in electronic counting circuits.
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DELIQUESCENCE

Deliquescence is a change of form from the solid to the liquid state, by the absorption of moisture from the atmosphere. It occurs in many bodies, such as caustic potash, potassium carbonate, acetate of potassium, calcium chloride, copper chloride, zinc chloride, ammonium nitrate etc.
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DELTA METAL

Delta Metal is a variety of brass containing 55 percent copper, 41 percent zinc and 4 percent various other metals. It was invented in the 19th century (patented in 1883 - 1884) by Dick and the original delta metal contained a small portion of iron. Delta metal is of a yellowish or golden colour, and in certain respects superior to malleable iron or steel. It may be rolled either hot or cold, drawn out into wire, is easily forged, and becomes very fluid when melted, so as to be easily cast into small articles, being also very suitable for artistic objects. It does not rust, and was much used for fittings and parts of machinery of various kinds, for ships' sheathings and screws, tools, etc and was used in Geneva for making watch cases in 1885.
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DELTA RAYS

Delta rays are a stream of electrons moving at a relatively low velocity.
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DEMOGRAPHY

Demography is the study of the size, structure, dispersement, and development of human populations to establish reliable statistics on such factors as birth and death rates, marriages and divorces, life expectancy, and migration. Demography is used to calculate life tables, which give the life expectancy of members of the population by sex and age. Demography is significant in the social sciences as the basis for industry and for government planning in such areas as education, housing, welfare, transport, and taxation. Demographic changes are important for many businesses. For example, the fall in the number of people aged 10-20 during the 1980s and the first half of the 1990s has led to many school closures, a shrinkage in the potential market for teenage clothes, and a fall in the number of young people available for recruitment into jobs by employers. Equally, the forecast rise in the number of people aged 75+ over the next 20 years will lead to an expansion of demand for accommodation for the elderly.
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DENABY POWDER

Denaby powder is an explosive used in coal mining comprised of ammonium nitrate, alkali nitrate, TNT, and ammonium chloride.
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DENATURANT

A denaturant is a substance added to intoxicating liquids such as alcohol, so that while they are rendered unfit to drink are still usable in industry. However, the theory behind their use fails to appreciate the desperation of some alcoholics, and the drinking of methylated spirits despite being made more dangerous by the addition of toxic denaturants, is still just as widespread, but with even more injury occurring to those who consume it.
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DENATURATION

In chemistry, denaturation is the process of altering the structure of a protein by physical or chemical means.
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DENATURED ALCOHOL

Denatured alcohol is methylated spirit adulterated for industrial use with noxious substances making it unfit to drink.
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DENSITE

Densite is a Belgian coal-mining explosive comprised of alkaline nitrates, trinitrotoluene, dinitrotoluene, and ammonium chloride.
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DENSITY

In physics, density is the mass of a substance in relation to its volume (the quantityof matter contained in a body under a given bulk), and usually expressed as the weight in grams of one cubic centimetre. If a body of equal bulk with another contains double the quantity of matter it is of double the density. Or if a body contain the same quantity of matter as another, but under a less bulk, its density is greater in proportion as its bulk is less than that of the other. Hence the density is directly proportional to the quantity of matter, and inversely proportional to the bulk or magnitude. The relative quantities of matter in bodies are known by their gravity or weight, and when a body, mass, or quantity of matter is spoken of, its weight or gravity is always understood, that being the proper measure of the density or quantity of matter. The weights of different bodies, of equal bulks, indicate their relative densities. The density of solids, fluids, and gases, as compared with that of water, is their Specific Gravity. Since volume enters into this dimension, and volume varies with temperature, it is essential that the temperature at which the measurement was taken is revealed when stating the density of a substance.
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DENTAL FORMULA

Dental Formula is an arrangement of symbols and numbers used to signify the number and kinds of teeth of a mammiferous animal.
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DENTAL PLASTER

Dentl plaster is an unmodified hemi-hydrate gypsum plaster similar to plaster of Paris, but much more finely ground and generally produced from pure gypsum to produce a very good white colour. Dental plaster is generally used for dental surgery, but is also used in the paining and decorating trade.
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DEODORIZER

Deodorizers are chemical substances which have the power of destroying fetid effluvia, such as chlorine, chloride of lime, etc.
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DEOXYGENATION

In chemistry, deoxygenation is the process of removing water from a compound.
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DEPILATORY

A depilatory is a substance which has the power to remove hair other than by cutting it. The term is generally applied to cosmetic hair removers.
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DERAILLEUR

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A derailleur is a mechanism on a bicycle that effects gear changing by moving the chain from one sprocket wheel to another.
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DERRICK

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A derrick is a lofty, portable, temporary, crane-like structure consisting of a single post or pole, supported by stays and guys, to which a boom with a pulley or pulleys is attached, used in loading and unloading vessels, etc. They were invented in 1857 by Bishop for raising sunken vessels and named after the 17th century Tyburn hangman, Derrick.

In the USA, the term derrick describes a tower-like structure erected over a deep, bored well, especially an oil well, while the well is being bored.
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DERRICK-CRANE

A derrick-crane is a kind of crane combining the advantages of the common derrick and those of the ordinary crane. The jib of this crane is fitted with a joint at the foot, and has a chain instead of a tension-bar attached to it at the top, so that the inclination, and consequently the sweep, of the crane can be altered at pleasure.
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DESICCATOR

A desiccator is an apparatus used mainly in the laboratory, by which substances can be thoroughly freed from water.
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DESK

A desk is a flat or sloping table used for reading, writing or drawing, with or without legs. In the Middle Ages a plank was generally used.
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DESQVIEW

DESQview by Quarterdeck Office Systems is a now-obsolete character-based multitasking operating environment for DOS that let you open multiple application windows simultaneously and toggle between applications without losing your place. The product took full advantage of enhanced expanded memory to allow multitasking.
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DETONATING TUBE

A detonating tube is a species of eudiometer, being a stout glass tube used in chemical analysis for detonating gaseous bodies. It is generally graduated into centesimal parts, and perforated by two opposed wires for the purpose of passing an electric spark through the gases which are introduced into it, and which are confined within it over mercury and water.
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DETONIT

Detonit is a German explosive comprised of ammonium nitrate, charcoal, meal, 4 per cent blasting gelatine and neutral salts.
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DEUTERIUM

In chemistry, deuterium is an isotope of hydrogen having twice the mass of ordinary hydrogen.
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DEUTOXIDE

A deutoxide is a compound of two atoms of oxygen to one or more of a metal.
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DEVIL

A devil is a machine or mechanical contrivance with teeth or spikes that have a tearing action on fibres, such as wool or cotton, rags, etc.
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DEW

Dew is a deposition of water from the atmosphere upon the surface of the earth in the form of minute globules. During the day the earth both absorbs and emits heat, but after sunset its supply of warmth is cut off, though it still continues to radiate heat into the surrounding space. Grass, flowers, and foliage being good radiators, lose after sunset the heat which has previously been absorbed by them, without receiving any in return, and their temperature consequently falls considerably below that of the atmosphere. From the proximity of these cold substances the particles of vapour in the adjoining air are condensed and deposited upon their surfaces in the form of dew, or of hoar-frost where the temperature of the earth is below freezing.

When the sky is clouded the heat abstracted from the earth's surface by radiation is restored by the clouds, which, being good radiators, send back an equal amount of heat to what they receive; and a balance of temperature being thus maintained between the earth and the surrounding atmosphere, no dew is formed. The deposition of dew is likewise prevented by wind, which carries away the particles of air before the vapour contained in them has been condensed. Horizontal surfaces, and those which are exposed to a wide expanse of sky, receive a greater supply of dew than sheltered or oblique surfaces, where circumstances diminish the amount of radiation. The radiation from the earth's surface is one of those happy provisions for the necessities of living beings with which nature everywhere abounds.

The heavy dews which fall in tropical regions are in the highest degree beneficial to vegetation, which, but for this supply of moisture, would, in countries where scarcely any rain falls for months, be soon scorched and withered. But after the high temperature of the day the ground radiates under these clear skies with great rapidity, the surface is quickly cooled, and the watery vapour, which, from the great daily evaporation, exists in large quantities in the atmosphere, is deposited abundantly. This deposition is more plentiful also on plants, from their greater radiating power; while on hard, bare ground and stones, where it is less wanted, it is comparatively trifling.

In cold climates the earth, being cold and moist the clouds prevent the radiation of heat; the surface is thus preserved warm, and the deposition of dew is, in a great measure, prevented.
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DEW POINT

Dew-point is the temperature at which condensation of the vapour in the air takes place. When the temperature of the air has been reduced by radiation to the dew-point, dew is deposited and an amount of heat set free which raises the temperature of the air. Thus the dew-point will indicate what the minimum temperature of the night is likely to be, a knowledge of which is useful to the horticulturist.
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DEW-RAKE

A dew-rake is a fine rake used on lawns.
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DEXTRIN

Dextrin is a strong adhesive derived from starch. It was formerly marketed under the name of 'British Gum'.
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DEXTRINE

Dextrine is a generic name applied to soluble gummy substances intermediate between starch and glucose. They are prepared from starch by the aid of dilute mineral acids or of malt extract, and are usually named according to the colour they give with iodine, e.g. erythro-dextrine, etc. When heated with dilute acids they are transformed into glucose. The composition is the same as that of starch. They are white, insipid, without smell, and are good substitutes for gum-arabic.
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DI(2-ETHYLHEXYL) PHTHALATE

Di(2-ethylhexyl) phthalate, also commonly called bis (2-ethylhexyl) phthalate, is a colourless, oily liquid with a slight odour. It was patented in 1933, and is primarily used as one of several plasticisers in polyvinyl chloride (PVC) resins for fabricating flexible vinyl products. These PVC resins have been used to manufacture teething rings, pacifiers, soft squeeze toys, balls, shower curtains, raincoats, adhesives, polymeric coatings, components of paper and paperboard, defoaming agents, enclosures for food containers, animal glue, surface lubricants, flexible devices for administering parenteral solutions, and other products that must stay flexible and uninjurious for their lifetime. It is also used to manufacture vinyl gloves used for medical examinations and surgery. As a non-plasticizer, di(2-ethylhexyl) phthalate is used as a replacement for polychlorinated biphenyls (PCBs) in dielectric fluids for electric capacitors. It is also used as a solvent in erasable ink, an acaricide for use in orchards, an inert ingredient in pesticides, a component of cosmetic products, and a vacuum pump oil; it is used to detect leaks in respirators and to test air filtration systems. Di(2-ethylhexyl) phthalate is insoluble in water, miscible with mineral oil and hexane, and soluble in most organic solvents. It is easily dissolved in body fluids such as saliva and plasma. Di(2-ethylhexyl) phthalate is a combustible liquid; it may burn, but does not readily ignite. It produces poisonous gas in a fire. When heated to decomposition, it emits acrid smoke. Di(2-ethylhexyl) phthalate is also known as bis(2-ethylhexyl) phthalate, bis(2- ethylhexyl)-1,2-benzenedicarboxylate, di(2-ethylhexyl)ortho-phthalate, di-sec-octyl phthalate, 2- ethylhexyl phthalate, NCI-c52733, disec-octyl phthalate, 1,2-benzenedicarboxylic acid, bis (2- ethylhexyl) ester, DOP, DEHP, and octoil.
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DIACOUSTICS

Diacoustics is a now obsolete term for the science of refracted sounds.
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DIAGONAL SCALE

A diagonal scale is a scale which consists of a set of parallel lines dravrn on a ruler, with lines crossing them at right angles and at equal distances. One of these equal divisions, namely, that at the extremity of the ruler, is subdivided into a number of equal parts, and lines are drawn through the points of division obliquely across the parallels. With the help of the compasses such a scale facilitated the laying down of lines of any required length to the 200th part of an inch in the pre metric system used in Britain.
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DIALYSIS

Dialysis is a method of chemical analysis, depending upon the different degrees of diffusibility of substances in liquids. It was discovered by Thomas Graham in 1861.
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DIAMAGNETIC

Diamagnetic is a term applied to substances which, when under the influence of magnetism and freely suspended, take a position at right angles to the magnetic meridian, that is, point east and west. From the experimennts of Faraday it appears that all matter is subject to the magnetic force as universally as it is to the gravitating force, arranging itself into two great divisions, the paramagnetic and diamagnetic. Among the former are iron, nickel, cobalt, platinum, palladium, titanium, and a few other substances; and among the latter are bismuth, antimony, cadmium, copper, gold, lead, mercury, silver, tin, zinc, and most solid, liquid, and gaseous substances. When a paramagnetic substance is suspended freely between the poles of a powerful horse-shoe magnet it points in a line from one pole to the other, which Faraday terms the axial line. On the other hand, when a diamagnetic substance is suspended in the same manner it is repelled alike by both poles, and assumes an equatorial direction, or a direction at right angles to the axial line.
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DIAMETER

Diameter is the straight line drawn through the centre of a circle, and touching the two opposite points of the circumference. It thus divides the circle into two equal parts, and is the greatest chord. The length of the diameter is to the length of the circumference of the circle as 1 to 3.14159265..., the latter number being an interminable decimal.
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DIAMOND HAMMER

A diamond hammer was a hammer or pick provided with several sharp-pointed teeth and used for giving a uniform roughness to the surface of a millstone which is was used for whetting. The term diamond hammer was also applied to a steel pick with a diamond-shaped point at each extremity which was used for recutting grooves in stone.
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DIASTASE

Diastase is a complex nitrogenous organic compound contained in germinating barley, oats, saliva and in the secretions of the pancreas. It is an enzyme which causes the fermentation of starch first into dextrine and then into glucose. The diastases from different sources are perhaps different. It is obtained by digesting in a mixture of three parts of water and one of alcohol, at a temperature of 113 Fahrenheit, a certain quantity of germinated barley ground and dried in the open air, and then putting the whole under pressure and filtering it. Diastase is solid, white, and soluble in water and dilute alcohol, but insoluble in strong alcohol.
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DIATHERMANCY

Diathermancy is the property that is possessed in various degrees by different substances of transmitting radiant heat. Bodies that are equally transparent, that is, bodies which have equal power of transmitting rays of light, are very different in their power of transmitting heat rays. Thus a thin plate of glass and a thin plate of rock-salt may be nearly equally transparent, but the plate of rock-salt has far superior power of transmitting rays of heat. The latter, it has been found, allows 92 per cent of the total heat from any source to pass; glass only 39 per cent from a lamp flame, 24 per cent from incandescent platinum, etc. Rock-salt is the only body equally diathermanous to heat from all sources. The diathermancy of the plates in every case decreases very rapidly as their thickness is increased.
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DIAZO COMPOUNDS

Diazo Compounds are a group of organic compounds characterised by the presence of the group -N2-. They are prepared by means of the diazo reaction, which consists in treating a primary aromatic amine with nitrous acid. Salts of this type are used in the production of dyestuffs.
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DICHLOROETHANE

1,2-Dichloroethane is a clear, thick man-made liquid that is not found naturally in the environment. It has a pleasant odour and sweet taste. It is used primarily to make vinyl chloride and a number of other solvents that remove grease, glue, and dirt, including trichloroethane, trichloroethylene, perchloroethylene, vinylidene chloride, and ethyleneamines. It is also found in commercial solvents used by industry to clean cloth, remove grease from metal, and break down oils, fats, waxes, resins, and rubber. In the household, 1,2-dichloroethane can be found in some cleaning agents and pesticides; in some adhesives, such as those used to glue wallpaper or carpeting; and in some paint, varnish, and finish removers. It is also added to leaded petrol to prevent engine knock.


1,2-Dichloroethane is used as an insect fumigant for stored grains and in mushroom houses, as a soil fumigant in peach and apple orchards, and as an extractant in certain food processes.
1,2-Dichloroethane is volatile at room temperature; it is flammable and burns with a smoky flame. Small amounts of 1,2-dichlorethane released in water or onto soil can vaporize into the air. It does not remain in the air for very long but can remain in water for possibly more than 40 days. 1,2-Dichloroethane is miscible with alcohol, chloroform, ether, and chlorinated solvents, and soluble in common organic solvents. It is sparingly soluble in water. When heated to decomposition, it produces toxic fumes of hydrochloric acid. Other names for 1,2-dichloroethane are 1,2-ethylene dichloride; aethylenchlorid; alpha, beta-dichloroethane; borer sol; di-chlor-mul-son; dichloro-1,2-ethane; dichloroethylene; Dutch liquid or oil; ethane dichloride; ethane 1,2-dichloride; ethyleen dichloride; ethylene chloride; ethylene dichloride; freon 150; glycol dichloride; and sym-dichlorothane.
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DICHLOROPROPANE

1,2-Dichloropropane is a colourless liquid belonging to a class of chemicals referred to as volatile organic compounds (VOCs). It is a man-made chemical used only in research and industry. High-purity 1,2-dichloropropane is marketed as a solvent. 1,2-Dichloropropane is also used as an intermediate in the synthesis of carbon tetrachloride, lead scavenger in petrol, textile stain remover, oil and paraffin extractant, scouring compound, and metal degreasing agent, especially prior to electroplating. Prior to the early 1980s, it was used agriculturally as a pesticide for citrus fruits, pineapple, soy beans, cotton, tomatoes, and potatoes. 1,2-Dichloropropane had been sold for consumer use in paint strippers, paint varnish, and furniture finish removers, as a low-cost alternative to methylene chloride, but those uses were discontinued by 1983. By the end of 1983, its use as a solvent for film production was also being phased out. 1,2-Dichloropropane has a chloroform-like odour and evaporates rapidly at room temperature. Degradation in both the atmosphere and groundwater is slow. It is a flammable liquid and produces poisonous gases, including chlorine, in a fire. Containers of the chemical may explode in fire. Vapours form flammable mixtures with air and may travel to a source of ignition and flash back. It is slightly soluble in water. 1,2-dichloropropane is also known as propylene dichloride; propylene chloride; 2,3-dichloropropane; and 1,2-D.
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DICHROIC MIRROR

A Dichroic mirror is a mirror consisting of a glass plate on which is deposited a very thin film of metal. It will transmit light of a particular colour, but reflects light of other colours.
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DICHROOSCOPE

The dichrooscope is an optical apparatus invented by professor Dove of Berlin in 1860 for representing the interferences, spectra in coloured lights, polarisation of light etc.
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DICHROSCOPE

A dichroscope is an optical instrument, usually consisting of an achromatized double-image prism of Iceland-spar, fixed in a brass tube, which has a small square hole at one end and a convex lens at the other, of such a power as to give a sharp image of the square hole. On looking through the instrument the square hole appears double, and if a dichroic crystal is placed in front of it the two images will appear of different colours.
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DICTAPHONE

Dictaphone is a proprietary name for a machine, originally on the gramophone principle, that records speech and will subsequently reproduce it for transcription etc. Typically such devices are used within office environments, memorandums and letters being dictated into the machine, recorded, and then later played back to be typed up an audio typist. Early dictaphones recorded onto a waxed cylinder, modern equivalents record onto magnetic tape or more recently memory wafers.
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DIE

A die is a metallic stamp for impressing a design or figure upon coins or other metallic objects - a process known as die-sinking.
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DIE-CASTING

Die-casting is a method of casting metals by forcing them under pressure into moulds of a strong and permanent character capable of repeated use. Die-casting is said to have originated with the advent of printing, which necessitated the production of sharply cast types in large numbers.
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DIE-SINKING

Die-sinking is the art of preparing dies for stamping coins, buttons, medallions, jewelry, fittings, etc.

The steel for the manufacture of dies is carefully selected, forged at a high heat into the rough die, softened by careful annealing, and then handed over to the engraver. After the engraver has worked out the design in intaglio the die is put through the operation of hardening, after which, being cleaned and polished, it is called a matrix. This is not, however, generally employed in multiplying impressions, but is used for making a punch or steel impression for relief. For this purpose another block of steel of the same quality is selected, and, being carefully annealed or softened, is compressed by proper machinery upon the matrix until it receives the impression. When this process is complete the impression is retouched by the engraver, and hardened and collared like the matrix. Any number of dies may now be made from this punch by impressing upon it plugs of soft steel. From the end of the 19th century the earlier process of dies-sinking was commonly replaced by patterns engraved upon rollers for transference to sheet metal by rolling pressure.
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DIELECTRIC

Dielectric is the name given to any medium through or across which electrostatic induction can take place. The application of an electric field to a dielectric results only in a displacement of electric charge within the material, due to the molecules becoming polarised and orientating themselves in the direction of the electric field. Faraday first showed that electrostatic induction was not action at a distance, but took place by means of the insulating medium separating the two conductors. The medium he named a dielectric, and measured its specific inductive capacity by taking that of common air as unity.
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DIETHANOLAMINE

Diethanolamine (DEA) is a detergent.
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DIETHEROSCOPE

The dietheroscope is an apparatus for godesy and teaching optics. It was invented by Luvini of Tunis in 1876.
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DIETHYL PHTHALATE

Diethyl phthalate is a manufactured, colourless, oily liquid with a slight aromatic odour and a bitter taste. It is commonly used to make plastics more flexible, in products such as toothbrushes, automobile parts, tools, toys, and food packaging. It is also used in insecticides, mosquito repellents, aspirin, and cosmetics, including bath preparations, eye shadows, hair sprays, wave sets, nail polish, nail polish remover, nail extenders, detergents, aftershave lotions, and skin care preparations. Diethyl phthalate is used to manufacture celluloid; as a solvent for cellulose acetate in varnishes; as a fixative for perfumes; as a wetting agent; as a camphor substitute; as a dilutent in polysulphide dental impression materials; and as a solvent for nitrocellulose and cellulose acetate. It is used as a plasticizer in solid rocket propellants and cellulose ester plastics such as photographic films and sheets, blister packaging, and tape applications.
Diethyl phthalate is soluble in alcohol, ether, acetone, benzene, vegetable oils, ketones, esters, aromatic hydrocarbons, and aliphatic solvents. It is compatible with polar polymers and additives over a wide range of compositions. When heated to decomposition, it emits acrid smoke.
Diethyl phthalate is also known as 1,2-benzenedicarboxylic acid diethyl ester; ethyl phthalate; diethyl o-phthalate; o-benzenedicarboxylic acid diethyl ester; diethyl ester phthalic acid; phthalol; DEP; and diethyl-o-phenylenediacetate.
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DIFFERENTIAL CALCULUS

Differential calculus is a mathematical method of treating the rates of change of variables and affords methods of finding tangents to curves, maximum and minimum values, etc.
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DIFFERENTIAL GEAR

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In mechanics, a differential gear (sometimes abbreviated to simply a differential) is an arrangement of gear wheels connecting two shafts whose axles are in the same line forming a rigid coupling when the shafts turn at the same speed, but permitting them to turn at different speeds if necessary. Differential gears are used on motor vehicles to permit the outer driving wheel to turn faster on a curve.
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DIFFERENTIAL THERMOMETER

A differential thermometer is an instrument for determining very minute differences of temperature. Before microelectronics, Leslie's differential thermometer consisted of two glass bulbs containing air connected by a bent tube containing some sulphuric acid, the movement of which (as the air expands and contracts) served to indicate any slight difference of temperature between the two bulbs.
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DIFFRACTION

Diffraction is a term applied to certain phenomena connected with the modification that rays of light undergo in passing close to the edge of an opaque body. Thus when a beam of direct sunlight is admitted into a dark room through a narrow slit, and falls upon a screen placed to receive it, there appears a line of white light bordered by coloured fringes; these fringes are produced by diffraction.
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DIFFUSION

Diffusion is the gradual mixing of gases or liquids when brought into direct contact. Thus, in the case of gases, when a jar of oxygen and a jar of hydrogen are connected together by a tube or opening of any kind, they rapidly become mixed; and their mixture does not depend on gravity, but takes place in opposition to that force, as may be shown by placing the jar of hydrogen gas above the other. Oxygen is sixteen times heavier than hydrogen, bulk for bulk, but the heavier gas moves upwards and the lighter downwards, and the process of intermixture, or diffusion, goes on until the two gases are apparently equably distributed throughout the whole space. After that they have no tendency whatever to separate.

Similarly, if two vessels, one containing oxygen and the other hydrogen, be connected by a tube which is stuffed with a plug of porous material, such as plaster of Paris, the gases gradually diffuse one into the other through the porous plug. The two gases, however, do not pass through the porous separator at equal rates, but in inverse proportion to the square roots of the densities of the gases. Thus in the case of two vessels, one containing hydrogen and the other oxygen, which is sixteen times as heavy as hydrogen, the hydrogen will pass towards the oxygen jar four times as quickly as the oxygen will pass towards the hydrogen jar.

Kindred phenomena occur when two liquids that are capable of mixing, such as alcohol and water, are put in contact, the two gradually diffusing one into the other in spite of the action of gravity. In some cases, however, as where ether and water are employed, the diffusion is only partial, this result arising from the fact that these two liquids are not miscible in all proportions. When solutions of various solid bodies are placed in contact, interdiffusion also takes place. On the results of his examination of the phenomena of diffusion of liquids and salts across porous membranes or septa, Graham founded a method of separating colloid from crystalloid bodies, which he called dialysis.
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DIGESTION

Digestion is the process of absorbing and distributing substances from ingested food to the body.
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DIGITAL PAD

Digital pad is a computer program for the PC designed as a smart alternative to pen and paper, it allows you to leave a message on your bosses computer. An notification icon will appear in the system tray notifying him or her of the new message. This program supports in-box, history, background running, multi-user functionality, and various other features.
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DIGITAL SIGNAL PROCESSING

Digital signal processing (DSP) is circuitry in which analog signals, such as audio or radio signals, are converted into digital form, manipulated and processed while in digital form, and then converted back to analog form.
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DIGITAL SIGNAL PROCESSOR

In electronic engineering, a digital signal processor (DSP) is a specialized circuit, usually a chip, that is designed to manipulate large quantities of data in real-time.
Digital signal processor circuits are employed in audio circuits as well as in signal detection in radios and in radios for digital IF filters, noise reduction circuitry and the cancellation of beat sounds in radio circuits.
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DIHYDROXYPHENYLALANINE

Dihydroxyphenylalanine (dopa) is an intermediate in the natural synthesis of adrenaline and of the pigment melanin. In the nervous system, dihydroxyphenylalanine is converted first to dopamine and then to noradrenaline and then to adrenaline.
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DILATOMETER

A dilatometer is an apparatus used to measure changes in volume of solids. The solid is placed in a glass bulb with a capillary tube, and the bulb and part of the tube are filled with a liquid which is without action on the solid. By observing the liquid's position in the tube, changes in the volume of the solid may be measured.
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DIMETHICONE

Dimethicone gives a smooth feel to a cosmetic cream or lotion. Various allergic reactions and internal problems make it questionable as a cosmetic ingredients. Although it's still widely used, many herbal oils, such as vegetable glycerine, can easily replace it.
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DIMORPHISM

Dimorphism is a special case of polymorphism; the state when the same substance can appear in two different crystalline forms. Ice for example can exist as ordinary light ice, or if frozen below minus 20 degrees and subjected to high pressure forms dense ice which is heavier than water.
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DINITROTOLUENE

There are no natural sources of Dinitrotoluene (DNT), which is usually manufactured by mixing toluene with nitric acid in the presence of concentrated sulphuric acid. This reaction produces a mixture which consists of approximately 80% of the 2,4-isomer and 20% of the 2,6-isomer. Also produced are small quantities of other DNT isomers. Small concentrations of DNT isomers also occur as by-products in the production of trinitrotoluene (TNT). 2,4-DNT and 2,6-DNT are used primarily as intermediates in the production of flexible polyurethane foams used in the bedding and furniture industry. DNT is also used in the production of munitions and explosives, for which DNT is a gelatinising and waterproofing agent. It is also used as an intermediate in the manufacture of dyes, and as a purified form, in smokeless gunpowder. 2,4-DNT is a highly reactive chemical and is a dangerous explosion hazard. It is combustible and may burn, but does not readily ignite. Poisonous gas is produced in a fire in which 2,4-DNT is burning. It is slightly soluble in water and soluble in alcohol ether, acetone, or benzene. 2,6-DNT is soluble in alcohol. 2,4-DNT is also known as benzene,1-methyl-2,4-dinitro-; and 2,4-dinitrotoluol. Synonyms for 2,6-DNT are benzene, 2-methyl-1, 3-dinitro-; and 2,6-dinitrotoluol.
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DIODE

A diode is a thermionic valve with two electrodes, or a semi-conductor equivalent. It presents a high resistance one way around and a low resistance the other.
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DIOPTRICS

Dioptrics is that part of optics which deals with the refraction of light passing through different mediums, as through air, water or glass, and especially through lenses. These phenomena, however, are now more commonly treated under the head of refraction.
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DIPHENYL

Diphenyl is an alternative name for Phenyl benzene.
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DIPLEIDOSCOPE

A dipleidoscope is an instrument for indicating the passage of the sun or a star over the meridian, by the coincidence of two images of the object, the one formed by single and the other by double reflection. It consists of an equilateral hollow prism, two of whose sides are silvered on the inside so as to be mirrors, while the third is formed of glass. The prism is adjusted so that one of the silvered sides shall be exactly in the plane of the meridian, and the transparent side towards the object.
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DIPOLE AERIAL

A dipole aerial is an aerial consisting of two straight conductors mounted in line, the connection being made to the two inner ends. A half-wave dipole aerial is constructed on the basis that an aerial conductor insulated at its ends will exhibit a resonance when its electrical length is exactly one half-wavelength. In this condition an incoming electromagnetic wave will induce currents which set up standing waves of current and voltage, by successive reflections from the insulated ends of the conductor, as the induced oscillating currents travel along it. Radio signals supplied to the conductors similarly cause standing waves to be set up on the conductors which energise the surrounding atmosphere, maximum radiation occurring within an arc of 78 degrees perpendicular to the plane of the aerial when the dipole is mounted horizontally, thus providing a basically bi-directional transmission/reception pattern. A vertically mounted dipole exhibits a unidirectional radiation and reception pattern.

The distribution of current is a maximum at the centre of the conductor length and zero at its ends, where reflection occurs; correspondingly, the voltage is at a minimum at the centre and rises to a maximum at the ends of the conductor. Because of physical effects, the physical length of the conductor is actually shorter than the electrical length, and the impedance at the centre is approximately 70 ohms, the actual impedance being effected by near by physical objects (a theoretical perfect half-wave dipole has a centre impedance of 73.12 ohms).

Since a dipole is tuned to a particular frequency, it is suitable for narrow-band transmission and reception. By adding a solid conductor above a dipole at a distance of 1/16th of a wavelength, and joining it at each end to the dipole elements a 'folded' dipole aerial is created which exhibits a higher feed point impedance of around 300 ohms, and is also resonant over a wider frequency range than the simple dipole.
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DIPPING-NEEDLE

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A dipping-needle or inclination compass is an instrument for showing the direction of one of the components of the earth's magnetism. In essentials the instrument consists of a light, magnetized steel bar supported on a horizontal axis which passes, as nearly as possible, through the centre of inertia of the bar. When a needle thus mounted is placed anywhere not in the magnetic equator, it dips or points downward; and if the vertical plane, in which it moves, coincides with the magnetic meridian the position of the needle shows at once the direction of the magnetic force. The intersection of two or more directions found by making the experiment at different places, indicates the place of the magnetic pole.
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DIPTYCH

A diptych was a two-leaved tablet of metal, ivory or other material used by the Greeks and Romans. In the early Christian church it was customary to inscribe the names of deceased bishops on
diptychs. This practise was extended to include other distinguished persons who had deserved well of the church, and from it arose the calendars and martyrologies of a later period.
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DIRECT ACCESS

Direct access is a method of extracting information from a computer memory. Information stored in a type of memory that supports direct access, such as random-access memory and magnetic disk, can be retrieved, or accessed, immediately regardless of its location within the memory.
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DIRECTRIX

In mathematics, a directrix is a line perpendicular to the axis of a conic section, and so placed that the distance from it of any point in the curve is to the distance of the same point from the focus in a constant ratio. The name is also given to any line, whether straight or not, that is required for the description of a curve. The directrix of a parabola is a line perpendicular to the axis produced, and whose distance from the vertex is equal to the distance of the vertex from the focus.
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DISACCHARIDE

A disaccharide is a sugar of which the molecules are made up of two simple sugars, for example sucrose which is composed of glucose and fructose.
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DISC-WHEEL

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In mechanics, a disc-wheel is a form of worm-wheel in which a spiral thread on the face of the disc drives a spur-gear, moving it the distance of one tooth at each revolution. The shafts are at right angles to each other.
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DISINFECTANT

A disinfectant is a substance applied to the outside of the body, or to non-living material in order to kill any micro-organisms which may be present.
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DISK HARROW

The disk harrow was a revolutionary era in harrow design invented around 1865 in the USA. Prior to the disk harrow, almost all harrows consisted of square-toothed devices with the teeth set at right angles to a wooden frame. As the harrow was drawn the teeth were square against the soil and the implement required a heavy draft animal to pull it. The teeth quickly became clogged and were imperfect pulverizes pushing clods of earth to the side rather than reducing them to powder. The disk harrow replaced the traditional square teeth with broad, thin blades of iron, inclining backward, so as to prevent them clogging with roots, weeds or other rubbish, or being caught on other obstructions and facilitating an easier draught. At the same time, these new teeth gave a side motion to the earth like the mold-board of a plough, and turned and pulverized it.
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DISK PIECHARTER

Disk Piecharter by Zorn Software is a Windows Filemanager extension that graphically shows disk usage per directory and per file. It allows you to zoom in and out on pie chart segments, and enables you to delete whole directory trees (if desired) and shows the effect on free disk space.
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DISPERSION

In optics, dispersion refers to the angular separation experienced by the component rays of a pencil of light on emerging from a refracting medium, whose surfaces are not parallel to each other, eg the common prism. The length of the spectrum and the relative space occupied by the coloured rays vary greatly according to the refracting medium, the spectrum from a prism of oil of cassia being two or three times longer than one formed by a glass prism.

In chemistry, dispersion refers to colloidal particles suspended in a liquid medium.
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DISSECTION

Dissection is the process of cutting away and separating parts of a body, whereby its formation and the relationships of its parts can be observed.
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DISSOCIATION

Dissociation is the name given to a special case of chemical decomposition, such that the products can recombine to give the original substance when the temperature is lowered or when the conditions are altered. The decomposition of calcium arbonate (chalk) into lime and carbon dioxide is an example of dissociation, since these products recombine to form calcic carbonate under slightly different conditions. The decomposition of water at high temperatures is another example.
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DISSOLVING VIEWS

Dissolving Views were a form of early cinematographic entertainment in which paintings upon glass magnified and thrown with great distinctness upon a screen by means of one or two projectors (known as magic lanterns) with strong lenses, and illuminated by oxyhydrogen light. If one lantern was used the picture was drawn out of focus gradually, and a second substituted, which was brought gradually into focus, thus producing the haze and brilliancy which gained this sort of exhibition its name. When two projectors (lanterns) were used, they were placed side by side with their lens tubes slightly convergent, so that the images could be superposed on the screen. By means of a revolving shutter either lantern could be wholly or partially shut off and the image of other lanterns be correspondingly disclosed.
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DISTAFF

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A distaff was the first instrument employed in spinning. It consisted of a staff, on one end of which the wool or flax was rolled. The spinner held it in the left hand, and drew out the fibres with the right, at the same time twisting them. A small piece of wood called a spindle was attached to the thread, the weight of which carried it down as it was formed. When the spindle reached the ground the thread which had been spun was wound round it, and it was then again fastened near the beginning of the new thread.
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DISTILLATION

Distillation is the volatilization and subsequent condensation of a liquid in an apparatus known as a still and heated by a fire or flame. The operation is performed by heating the crude liquid or mixture in a retort or vessel known as the body of the still. This is made of various shapes and materials, and is closed with the exception of a slender neck which opens into the condenser, a long tube through which the hot vapour from the still is passed. The tube is kept at a sufficiently low temperature to cause the vapour to condense, the common method of securing this being to surround the tube with a constantly renewed stream of cold water. In some cases ice or a freezing mixture may be required to effect condensation. On a large scale the condensing tube is coiled round and round in a tub or box, and is known as a worm. From the end of it the vapour condensed into a liquid drops into a receiver.

The simplest case of distillation is that of water containing solid matter in solution, the solid matter remaining behind in the still or retort while the water trickles pure into the receiver, through a worm made of block-tin, as most other metals are attacked by distilled water.

When the mixture to be distilled consists of two or more liquids of different boiling-points, such as alcohol and water, the more volatile comes off first, accompanied by a certain proportion of the vapour of the other, so that it is hardly possible completely to separate bodies by one distillation. This is effected by repeated successive distillations of the liquid with or without the addition of substances to retain the impurities. When the production of one of the ingredients only is aimed at by this process, it is called rectification, but when it is desired to separate and collect all the liquids present, or to divide a mixture into portions lying within certain ranges of temperature ascertained either by the thermometer or by the amount of liquor run off, or by the appearance of the distillate, etc, the process is called fractional distillation.

In the laboratory, distillation is employed for purifying water, for recovering alcohol and ether, for the preparation, purification, and separation of a great number of bodies. On the large scale distillation is employed in the preparation of potassium, sodium, zinc, mercury; of sulphuric acid, ether, chloroform, sulphide and chloride of carbon, essential oils and perfumes; purification of coal and wood tar, and the products obtained from them; and on an extensive scale in the manufacture of whisky, brandy, or other spirit.

The distillation of whisky has long been familiar in Britain, especially in Scotland and Ireland, and by the old pot-still is a simple operation indeed, and one that even yet is practised surreptitiously in out-of-the-way localities. On the large scale more elaborate apparatus are employed, and for alcohol of a cheap class Coffey's or other patent still is much used. Copper is the metal that suits best as the material for the stills used in distilling whisky. Sea-water is distilled in many cases for drinking or cooking purposes. This water is, of course, very pure, but its taste is rather mawkish.

Destructive distillation, or dry distillation, differs from the preceding in this respect, that the original substance is not merely separated into the bodies by the mixture of which it is formed, but is so acted on that it is completely decomposed, and bodies are produced which had no existence in the original matter. The term is restricted to the action of heat upon complex organic substances out of contact with the air. The products of destructive distillation are numerous and varied. On the manufacturing scale the process is conducted sometimes for one part, sometimes for another part of the products. Coal, for example, may be distilled primarily for the gas, but also for ammoniacal water, benzene, anthracene, as well as for the sake of the fixed carbon or coke, the volatile portions being too often neglected and practically wasted. But much more economical methods of making coke are now practised than formerly.

Wood is distilled partly for the sake of the pyroligneous acid and the tar, partly for the charcoal. Bones are distilled for the sake of the charcoal, though the oil is also collected. Shale is distilled both for the oil and for the paraffin wax, ammonia, etc, obtained.
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DISTRIBUTED PROCESSING

Distributed processing is a system of processing data in which several computers are used at various locations within an organization instead of using one central computer. The computers may be linked to each other in a network, allowing them to cooperate, or they may be linked to a larger central computer, although a significant amount of the processing is done without reference to the central computer.
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DISTRIBUTOR

In a car, the distributor distributes electrical pulses to the spark plugs.
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DITCH

A ditch is a narrow channel dug in the earth, usually for drainage, irrigation or as a boundary marker.
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DITHERING

In digital audio engineering dithering is a mathematical process where a random noise is added to the least significant bit of a digital word. With very low level signals, the quantization error becomes correlated to the signal level. This creates a measurable amount of distortion. By adding dither, the correlation between the signal level and the quantization error is cancelled, allowing the digital system to encode amplitudes smaller than the least significant bit. If you change the word size as a signal passes from one digital system to another, being able to add dither allows you to maintain a high quality signal.
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DIVISION

In arithmetic, division is the dividing of a number or quantity into any parts assigned. It is one of the four fundamental rules, the object of which is to find how often one number is contained in another. The number to be divided is the dividend, the number which divides is the divisor, and the result of the division is the quotient. Division is the converse of multiplication.
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DMA

In computing, DMA is an abbreviation for Direct Memory Access. Direct memory access is a feature that improves microprocessor efficiency. In ordinary input/output operations, the processor (CPU) supervises the entire transfer of the data from a peripheral to the processor and then on to the destination memory location, or vice versa. In direct memory access, the processor allows the peripheral device to hold and control the data bus, transfering the data directly to and from memory without involving the processor. After the transfer has completed the peripheral releases its hold on the data bus and the processor resumes processing instructions from where it left off. Typically a Personal Computer DMA controller uses port addresses between 0000 and 0001E.
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DNOTE

Dnote by Acute Software, is a fast text editor for the Windows operating system, designed for people who use a lot of files at once, or who want to quickly view the contents of a file. It keeps a list of the commonly used directories, so that you don't have to keep going backwards and forwards through explorer looking for files.
Dnote features advanced search and replace facilities, convert to and from HTML, Autocontents (functions, comments and headings), insert ASCII characters as well as other text conversion features.
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DNS

In computing, DNS is a system that converts name-based addresses, such as www.probertencyclopaedia.com, into TCP/IP addresses and vice versa.
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DOBEREINER'S LAMP

Dobereiner's Lamp is a contrivance for producing an instantaneous light, invented by Professor Dobereiner, of Jena, in 1824. The light is produced by throwing a jet of hydrogen gas upon recently-prepared spongy platinum, when the metal instantly becomes red hot, and then sets fire to the gas. The action depends upon the readiness with which spongy platinum absorbs gases, more especially oxygen gas. Tlic hydrogen is brought into such close contact with oxygen (derived from the atmosphere) in the pores of the platinum that chemical union, attended with evolution of light, takes place.
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DODECAGON

A dodecagon is a twelve-sided regular polygon.
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DODECAHEDRON

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A dodecahedron is a regular solid bounded by twelve equal pentagons.
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DODECYL GALLATE

Dodecyl gallate (Lauryl gallate or n-dodecyl ester of 3,4,5-trihydroxybenzoic acid) is a white to creamy-white coloured, odourless solid, insoluble in water, soluble in ethanol and in fat, with a slightly bitter taste, used as an anti-oxidant in processed foods.
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DONARIT

Donarit is a German explosive consisting of ammonium nitrate 80 per cent, trinitrotoluene 12 per cent, rye-flour 4 per cent, nitro-glycerine 4 per cent.
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DONKEY ENGINE

A donkey engine is a small engine from two to four horse-power used in various operations where no great power is required. Thus a donkey-engine is often stationed on the deck of a ship to work a crane for loading and unloading.
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DOPE

Dope is a type of lacquer used in aircraft manufacture for the tautening and protection of stretched linen fabric.
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DOPPLER EFFECT

The Doppler effect is a change in observed wavelength due to relative motion between the source and observer.
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DORFIT

Dorfit is a German explosive comprising ammonium nitrate, trinitrotoluene, flour, salt and alkali nitrate.
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DOUBLE-BEAT VALVE

A double-beat valve is a type of valve, of washer shape, which has two seats, at the circumference and near the centre, thus affording a larger passage at a given lift than a plain disk.
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DOVETAIL SAW

A dovetail saw is a light hand saw, similar to a tenon saw but smaller, used for cutting fine tenons and dovetails.
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DR ANGUS SMITH'S PROCESS

Dr Angus Smith's process is a method of treating ferrour metal objects to prevent corrosion. The process consists of heating the article to 300 degrees Fahrenheit as soon as it is cast, and then immersing it in a prepared solution of coal tar which is then brought to the boil and allowe dto continue to boil until all the ammoniacal liquor, water and lighter oils have been expelled.
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DRAFIXCAD ULTRA

DrafixCAD Ultra by Foresight Resources, proves that high-quality computer-aided design and drafting do not have to cost a lot. This product includes features that you would expect to find only in much more expensive packages. DrafixCAD Ultra lets you create and manipulate a range of items including lines, arcs, ellipses, and polygons. Each item can possess numerous attributes that can be selected or changed at any time. Lines and arcs can be trimmed, divided, or stretched. Intersections can be rounded or bevelled. Symbols can be created, nested, and broken into their individual items. DrafixCAD Ultra allows you to copy, move, rotate, or scale an element, or mirror it about any axis. Elements may be designated by item, group, or region.
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DRAGON'S BLOOD

Dragon's Blood is a red resin obtained from the fruits of several East Indian trees such as Calamus Draco, Dracoena Draco, Pterocarpus Draco, &c. The material is a solid, soluble in alcohol and fatty oils, and used in the manufacture of furniture polishes, for staining marble and in some forms of printing, being a deep red dye. It is opaque, of a reddish-brown colour, brittle, and has a smooth shining conchoidal fracture.
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DRAGON'S-HEAD

In astronomy, dragon's-head is the name given to the symbol representing the ascending node of a planet.
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DRAGON'S-TAIL

In astronomy, dragon's-tail is the name given to the symbol representing the descending node of a planet.
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DRAKE R7

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The Drake R7 was an American made general coverage communications receiver manufactured from 1978 to 1981 and provided coverage from 10 kHz to 30 Mhz in AM, SSB, CW and RTTY modes. The main criticism of the Drake R7 was that it was a bit cumbersome to tune.
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DRAKE R7A

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The Drake R7A was an American made general coverage communications receiver manufactured from 1981 to 1983 and provided coverage from 10 kHz to 30 Mhz in AM, SSB, CW and RTTY modes. The Drake R7A was an upgraded model of the earlier Drake R7, and added more bandwidth selectivity options.
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DRAKE R8

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The Drake R8 was an American made general coverage communications receiver manufactured from 1991 to 1995 and provided coverage from 100 kHz to 30 Mhz in AM, SSB, CW, FM and RTTY modes.
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DRAKE R8A

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The Drake R8A was an American made general coverage communications receiver manufactured from 1995 to 1998 as a replacement for the Drake R8 and provided coverage from 100 kHz to 30 Mhz in AM, SSB, CW, FM and RTTY modes with many ergonomic and performance improvements added including: alphanumeric memories, faster scanning, improved AGC, improved notch, improved display, easier mode and bandwidth selection, tilt-bar, enhanced tone control, detachable line cord and an expanded RS-232 command set.
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DRAUGHT-SPRING

A draught-spring (draft-spring) is a spring invented by Sir Alexander Gordon and intervening between the tug or trace of a draught animal and the load, whereby a jerking strain upon the animal is avoided. Later draught-springs were fitted between railway carriages to lessen the violence of the jerk communicated to them when the train started moving.
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DRAW PLATE

Draw Plate is a plate of very hard steel or ruby, diamond or other hard stone, perforated with holes of graduated sizes through which metal rods are drawn successively to make them into wire.
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DREAMWAEVER 3

Macromedia's Dreamweaver 3 is an HTML design program that represents a major step forward in the evolution of WYSIWYG design tools. Instead of trying to protect you from HTML, Dreamweaver embraces it while still putting a full palette of design tools at your disposal. It's an extremely powerful program. Though it's tough to master, Dreamweaver is worth the trouble for anyone set on being a Web-design professional. Dreamweaver doesn't have a unified desktop you work with a series of floating modules that can be opened or closed depending on your immediate needs. Your actual workspace is the Document window, in which you build your page. You can conveniently drop elements into the Document window from Explorer or other sources. Highlight a specific asset or text, and a status bar at the bottom of the Document window displays the HTML tags that control what you've highlighted.
A configurable Launcher toolbar allows you to quickly manage and launch additional modules. The Site module, for instance, uses two windows to display local and remote files. You can transfer files via FTP by dragging them from one window to the other. The Library palette lets you drag assets, templates, styles, or complete style sheets to and from the Document window. The 'Behaviors' module performs like an object-oriented library, letting you drop events or actions onto text or graphics at will. And the History module not only stores your previous actions, but it also allows you to save them singularly or in groups to create a macro library. The program even has an HTML Source window, but because HomeSite ships with Dreamweaver, you're likely to use this only for simple, quick fixes. A separate Object palette provides easy access to common commands and special elements such as frames and forms. In addition, a context-sensitive inspector is always on hand. It displays and lets you edit information about whatever asset is currently highlighted. Dreamweaver' s learning curve is a small price to pay for a program this powerful, especially if it's a tool critical to your profession. Fortunately, the online help is well-constructed and navigable, and the consistent (if initially confusing) interface is strong enough to get you past any hurdles in a reasonable amount of time.
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DRESSER-COPPER

A dresser-copper is a vessel in which warps or threads are passed through boiling water.
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DRILL

A drill is a machine for boring holes in rock, metal or wood etc. Drill bits were greatly improved from the invention in the 18th century of the twist drill, consisting of a rod of steel with a deep channel cut into it in a spiral, and the end ground off at an obtuse angle to give two cutting edges and a very short point.
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DRIVER

In computing, a driver is a program that communicates between the computer hardware and the operating system. A popular example is a graphics driver which communicates between the graphics card and the operating system.
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DROP BLACK

Drop black is a good quality bone black produced by calcinating animal bones in closed retorts. Drop black is generally ground in terpentine and used as a spirit colour.
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DROSOMETER

A drosometer is an instrument for ascertaining the quantity of dew which falls. It consists of a balance, one end of which is furnished with a plate fitted to receive the dew, the other containing a weight protected from it.
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DRUMMOND LIGHT

The Drummond Light is a very intense light produced by turning two streams of gas, one of oxygen and the other of hydrogen, in a state of ignition upon a ball of lime. This light was invented in the 19th century by and proposed by Thomas Drummond to be employed in lighthouses.
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DRY ICE

Dry Ice is a commercial name for solidified carbon dioxide, often used as a coolant. It is called
dry ice because as it melts, it gives off a gas rather than a liquid, and so appears dry.
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DRY JOINT

In electrical terms, a dry joint is a soldered joint which, due to insufficient heating or lack of sufficient flux during the soldering operation, the solder has not adhered to the metals to be joined, thus producing a joint which is weak mechanically and of high electrical resistance.
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DRY-DOCK

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A dry-dock is a dock from which the water may be emptied to allow of convenient and expeditious ship- repairs.
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DRYING-OIL

Drying-oil is the name given to linseed and other oils which have been heated with lead oxide. They were for many years the bases of many paints and varnishes. When exposed to the air they absorb oxygen, and are converted into a transparent, tough, dry mass or varnish.
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DS1

In telecommunications, DS1 is a high-speed line capable of delivering 1.54 Mbps (1,540K) in both directions, and divided into 24 data-bearing channels.
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DS1C

In telecommunications, DS1C is a high-speed line capable of delivering 3.15 Mbps (3,150K) in both directions.
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DS2

In telecommunications, DS2 is a high-speed line capable of delivering 6.31 Mbps (6,310K) in both directions.
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DS3

In telecommunications, DS3 is a high-speed line capable of delivering 44.7 Mbps (44,700K) in both directions.
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DUCAT GOLD

Ducat gold is an alloy of copper and aluminium used in imitation of gold leaf. It is liable to tarnish, and is often lacquered to protect it.
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DUCKING

Ducking is an audio engineering term used to describe the automatic reduction of signal levels when the level of a source signal exceeds a specified threshold. It is used for voice-over applications where, for example, level of background music is automatically reduced, allowing an announcer to be heard clearly.
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DUCTILITY

Ductility is the property of solid bodies, particularly metals, which renders them capable of being extended by drawing, while their thickness or diameter is diminished, without any actual fraction or separation of their parts. On this property the wire-drawing of metals depends. The following is nearly the order of ductility of the metals which possess the property in the highest degree, that of the first mentioned being the greatest; gold, silver, platinum, iron, copper, zinc, tin, lead, nickel, palladium, cadmium. The ductility of glass at high temperatures seems to be unlimited, while its flexibility increases in proportion to the fineness to which its threads are drawn.
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DUODECIMAL SYSTEM

In numeration, the duodecimal system is a system of numbers the scale of which is twelve. Duodecimals is a term applied to an arithmetical method of ascertaining the number of square feet, etc, in a rectangular area or surface, whose sides are given in feet, inches, and lines.
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DUPONT PERMISSIBLE

DuPont Permissible is a coal-mining explosive used in the USA comprised of nitro-glycerine, ammonium nitrate, common salt.
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DURALUMIN

Duralumin is an alloy of aluminium, copper and magnesium, with traces of other metals. Typically duralumin is comprised of 94.4 percent aluminium, 4.5 percent copper, 0.95 percent magnesium and 0. 76 percent manganese. If properly tempered it has an extremely high tensile strength and is used in aircraft construction.
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DUTCH ENAMEL

Dutch enamel is an enamel prepared from linseed stand oil. Dutch enamels are not easy to apply, but dry with a brilliant lustre, have exceptionally good flow which results in a smooth surface free from brush marks and produce a tough, durable and elastic film.
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DUTCH METAL

Dutch metal is an alloy of about eleven parts of copper to two of zinc, the proportions varying according to the colour, which may be from copper to pale gold. The alloy is made into leaves like gold-leaf and is used for imitation gilding, either in leaf form or as powder.
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DUTCH PINK

Dutch pink is a yellow pigment obtained from quercitron - the bark of a North and Central American tree.
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DUTCH PROCESS

The Dutch process (or stack process) was formerly the principal method by which white lead was prepared. It consisted building a stack of earthenware pots containing acetic acid upon a thick layer of spent tan or manure and placing strips or coils of metallic lead over the pots; boards were then laid to forma false floor over the whole and more stacks built on top. The entire structure was then sealed and over time the metallic lead converted into lead carbonate by corrosion caused by the action of the acetic acid vapour in the presence of carbon dioxide.
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DWIM

DWIM is an acronym for Do What I Mean. It is a term used in artificial intelligence for computer self-correcting of errors.
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DX-2

DX-2 is a Japanese X.25-based public packet network first operated in 1979.
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DX-400

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The Realistic DX-400 was an American portable scanning communications receiver of the 1980's. The Realistic DX-400 was microprocessor controlled, had an LCD frequency display, direct push-button tuning, scanning facility and covered 150 kHz to 29.999 Mhz in AM mode, and 87.4 Mhz to 108 Mhz in FM wide mode. The Realistic DX-400 also had 6 AM and 6 FM memory channels.
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DYAD

In Chemistry, dyad refers to an elementary substance, each atom of which in combining with other bodies is equivalent to two atoms of hydrogen.
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DYE

A dye is a substance applied to material, usually a textile, for decorative purposes, to give it a colour different from that which it originally possessed.
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DYNAM

The dynam was a term proposed to express a unit of work equal to a weight of 1 Ib raised through 1 foot in a second ; a foot-pound.
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DYNAMETER

A dynameter (dyanometer) is an instrument used for measuring the magnifying power of telescopes. It consists of a small compound microscope, with a transparent plate, exactly divided, which is fixed to the tube of a telescope, in order to measure exactly the diameter of the distinct image of the eye-glass.
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DYNAMIC RANGE

In radio terms, dynamic range is a measure of the strongest received signal that a receiver can handle with overloading or distortion. It is measured in decibels. A minimum satisfactory measurement is 70 dB; over 100 dB is preferred.
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DYNAMICALLY RELOCATABLE CODE

In computing, dynamically relocatable code refers to programs that are position-independent. Dynamically relocation allows a multiprogramming or multitasking operating system to make effective use of available memory by writing inactive programs to a disk file, freeing the memory space they previously occupied and later reading the program from the disk file into any available memory location
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DYNAMICS

Dynamics is the science which deals with the laws of force in their relation to matter at rest or in motion, and as such it is differentiated from cinematics, which considers motion mathematically, and apart from the forces producing it. It is to Isaac Newton that we owe the clear statement of the three primary laws of force. These are: (1) that every body remains in a state of rest, or of uniform motion along- a straight line, unless it is compelled by force to change that state. (2) That change of motion is in proportion to the force employed, and occurs along the straight line in which the force acta. This change of motion includes both change of rate and of direction. (3) That, as the result of every action, there is also and always an equal reaction. These laws, which were formulated from experiment, involve the conception of force as a primary influence or action expressed in terms of space, time, and matter.

Dynamics is divided into two great branches: statics, which treats of solid bodies at rest under the action of forces; and kinetics, which treats of the action of forces in producing motion in solid bodies. Formerly the latter alone was called dynamics, and to this, in conjunction with statics, the general name mechanics was given. In the wide sense dynamics includes also hydrostatics.
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DYNAMITE

Dynamite is an explosive consisting of nitro-glycerine which has been absorbed into some inert material such as kieselguhr, sawdust or wood pulp. Dynamite was invented by Alfred Nobel in 1867, and was tried and approved in 1868. In 1875 a man named Thomson, Thomassin or Thomas made a time bomb with dynamite which he concealed upon the North German steamer Mosel with the intention of sinking it to claim the insurance on some goods he had on board. The bomb exploded while the ship was in dock for reasons unknown, killing more than 80 people and wounding another 200. Thomson confessed his crime and then killed himself.
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DYNAMMON

Dynammon is a coal-mining explosive comprised of ammonium nitrate, potassium nitrate and red charcoal.
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DYNAMO

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A dynamo (formerly known as a dynamo-electric machine) is a machine for converting mechanical energy into electrical energy. Dynamos differ from magneto-electric machines, which have a similar purpose, by the circumstance that in place of the permanent steel magnets which form a necessary part of a magneto-electric machine, electro-magnets are employed. In the original dynamo-electric machines the current by which the electromagnets were made was identical with the current given off by the machine, or else was a portion diverted from it; but in an important class of machines the current which makes the electro-magnets has an independent source, and to these machines the name 'dynamo' is also applied. The advantage of dynamo over magneto machines lies in their greater compactness, arising from the fact that electro-magnets are much stronger than permanent steel magnets of the same bulk. The extensive use of dynamos as the principal commercial sources of electric currents may be said to date from the improvements introduced in their construction by Gramme of Paris.
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DYNAMOMETER

A dynamometer is an apparatus for measuring power, or the rate of doing work, that is for measuring the force exerted by men, animals, or motors in overcoming some resistance. The resistance of a spring to extension or compression is the basis in some forms, weights or friction brakes are used in others. In absorption dynamometers, exemplified by friction brakes, the work done is dissipated as heat; in transmission dynamometers, the energy is utilized after measurement.
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DYNE

The dyne is the unit of force. One dyne is that force which, acting on a mass of one gram, imparts to it an acceleration of one centimetre per second per second.
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DYNOBEL

Dynobel is an explosive used in coal mining comprised of nitro-glycerine 15, collodion cotton 0.5, nitrobody 3, ammonium nitrate 46, wood-meal 5.5, salt 29.5, magnesium carbonate 0.5.
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DYSPROSIUM

Dysprosium is a rare metal element with the symbol Dy.
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