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The P band is the frequency band from 225 to 390 Mhz employed in radar.
 Research P Band
P-80 systems are an American bulletin board (BBS) and CD-ROM supplier specialising in pirated computer software (warez) for the PC and also information on computer hacking, phreaking and other illegal activities.
Research P-80 Systems
A pachometer or pachymeter is an instrument used for measuring thickness such as the tickness of the glass of a mirror, or the thickness of paper.
Research Pachometer
In the sense of communications, a packet is a structured group of binary digits in a prearranged sequence containing synchronism, address, control an error-checking data. Specialised synonym for a 'block' of data in CCITT Packet Data Network standards.
Research Packet
A Packet Switched Network is a network dedicated to the routing and delivery of data put in the form of standardised 'packets.'
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Packet Switching is the technique in which a stream of data is broken into standardised units called 'packets,' each of which contains address, sequence, control, size and error checking information in addition to the user data. Specialised packet switches operate on this added information to move the packets to their destination in the proper sequence and again present them in a contiguous stream.
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A padsaw or pad saw, is a small handsaw consisting of a narrow blade inserted into a handle, and used for cutting holes.
Research Padsaw
Paeonine or red coralline is an artifical red nitrogenous substance used as a dye. Paeonine is obtained by heating phenol with sulphuric and oxalic acid . It is used for dyeing silk and wool, and is also printed upon cotton.
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PageMaker was formerly a very popular, easy to use, WYSIWYG desktop publisher that allowed the design, layout, and production of typeset-quality documents on the Macintosh and PC running Windows. The product, one of the first desktop publishers for the Macintosh, provided a comprehensive set of tools for integrating text and graphics from virtually any Macintosh application into a professional-looking document. Nearly identical to PageMaker for the PC, this program offered user-defined style sheets, automatic text flow through a document, and 20 design templates. Rather than using a grid approach, PageMaker worked like a paste-up board on which to define the placement of elements on-screen after defining the number of columns the document will have.
PageMaker had a wide range of uses, from the occasional quick memo and graphics based publication, to a complex, content-oriented document with graphics (it was used to typeset the magazine Here's Health during the early 1990s). It was ideal for an environment using both PCs and Macs because a version was available for each machine and files could be transferred between the two environments.
When PageMaker was run a blank page was seen on-screen. Text and graphics could be imported using a place command to position the material as it was to appear on the printed output. The product retained formatting from word processing files such as tabs, type styles, justification, and proportional spacing. PageMaker had a built-in text editor which could also act as a basic word processor. Changes made in PageMaker were automatically reflected in the word processing document. The program automatically flowed text throughout the document and wrapped text around graphics. Its editing features controlled text size, style, typeface, multiple columns, and automatic hyphenation. Imported graphics could be sized, scaled, and cropped on-screen. Rules and line styles helped to position graphic images and text, and allow easy creation of boxed text, headlines, and framed images. Ruler guides controlled layout and column guides assisted in the actual placement and margins of graphics and text. PageMaker allowed the creation of style sheets. Users could see and work with multiple views of a page layout or two pages at once so that a double-page spread could be designed.
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Paints are mixtures of dry powder colours (pigments) with an oil or varnish vehicle. There are a number of classes of paints, for example those used for painting and decorating houses are much coarser than those used in the fine arts.
Research Paint
Palaeography is the study of ancient manuscripts written on papyrus, parchment or similar material, as distinct from epigraphy which is the study of ancient inscriptions incised on hard materials such as wood, stone or metal.
Research Palaeography
Palaeontology is a branch of biology and geology which deals with fossils. It is divided into palaeozoology and palaeobotany, which respectively have animals and plants as their subject matters.
Research Palaeontology
Palladium is a rare grey-white metal element with the symbol Pd. It has the power of absorbing a very large amount of hydrogen to which it is permeable when heated. It is used in an alloy with gold in dentistry and jewellery. In its pure form it is used for making watch springs and mirrors.
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Palm kernel oil (palm oil) is a fatty oil obtained from the kernels of the palm fruit and used in the manufacture of soap and margarine.
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Palmitic acid is a widely distributed naturally occurring fatty acid present in palm oil, with the formula C16H32O2.
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The Panasonic RF-B60 was a portable scanning radio introduced around 1987. The
Panasonic RF-B60 covered 522 khz to 1611 khz, 1615 khz to 29.999 Mhz in AM mode and 87.5 Mhz to 108 Mhz in FM wide mode.
Research Panasonic RF-B60
Panthenol (Pro vitamin B5) is the alcohol analogue of pantothenic acid. Whilst its vitamin properties are not proven in cosmetics and toiletries, it does have pronounced moisturising properties and gives and excellent ' skin feel' to products containing it.
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A pantograph is an instrument for mechanically tracing a figure similar to a given figure, but enlarged or diminished in a definite ratio. It consists of four rods forming a jointed parallelogram, with sides continued to convenient distances beyond the joints.
Research Pantograph
Pantothenic acid is a hydroxy acid found in plant and animal tissues that is one of the vitamin B complex of substances and is used for cell growth.
Research Pantothenic acid
Papain is a substance found in the juice of papaw. It has an identical action to Trypsin.
Research Papain
Para-cresol is a cresol found in bad eggs.
Research Para-cresol
A parachute is a rectangular or umbrella-shaped apparatus that allows a person or load attached to it to descend slowly from a height, especially from a balloon or aeroplane. The first human parachute descent was made in 1797, when Jacques Garnerin parachuted from a balloon over Paris. Folding parachutes were first used in America in 1880, and towards the end of the Great War aviators first used parachutes to escape from their aeroplanes. Early parachutes were made of canvas, and later silk. Modern parachutes comprise many separate panels of nylon, so that tears are confined to a small area. Until recently parachutes were umbrella-shaped, but parafoils (air-filled aerofoils) are now common. In addition to their use as safety devices, parachutes are used for sport, for aerial drops of supplies and equipment, and as braking devices (drogues) for landing aircraft or other vehicles.
Research Parachute
Paradichlorobenzene is a white crystalline, volatile substance which is insoluble in water of the benzene series. It has a penetrating odour and is used chiefly as a moth repellent.
Research Paradichlorobenzene
Paradox 3.0 was a relational database manager from Borland International, that, the manufacturers claimed, stuck a balance between functionality and ease of use. It offered the power of many of the advanced database products, yet was easy enough for the novice to use. It included enhanced relational operations, presentation-quality graphics, crosstab views, and enhanced query-by-example operators.
Paradox appealed to a wide range of users because it had menus as well as a programming language. The menus, which resembled the popular Lotus 1-2-3 interface, provided advanced capabilities to the beginning user, while the command language, Paradox Application Language (known as PAL), allowed sophisticated users to create complex turnkey systems and custom applications. PAL provided all the functions of competitive database programming languages. For those who used PAL to develop applications, Paradox also included an application generator that created PAL code which could be edited.
Paradox employed the artificial intelligence technique, query-by-example, to let users make multiple-file queries and database manipulations by giving an example of the kind of data wanted.
Paradox also used artificial intelligence to speed up queries by searching for the best path. Any index which Paradox created to answer a question would be used to answer a later query when appropriate. Paradox's multiforms capability allowed users to display records from multiple tables within a form and create forms with scrolling regions without any programming.
Paradox supported a multitable feature in its reporting capabilities. The most visual feature was the ability to create presentation-quality colour graphics such as pie charts, line, bar, and XY graphs. An automatic lookup function allowed the user to fill entire records just by filling in one field. This feature was excellent for creating invoices that automatically entered customer information on the invoice based on the entry of a customer number. As long as two files had a common field, information could be shared between them. This standard relational database feature enabled the user to have small manageable files instead of files that were cumbersome and difficult to work with. When searching for specific information, the user simply checked off the fields they wanted to see in the answer table.
Research Paradox
Paraffin is a colourless, tasteless, odourless, solid fatty family of hydrocarbons produced from the dry distillation of coal, shale, lignite, peat and the like. In Britain the term paraffin is often incorrectly applied to kerosene.
Research Paraffin
The term parallax describes the apparent movement of an object when viewed from two different positions.
Research Parallax
Parallel Transmission is the simultaneous transmission of all parts of a signal at one time; in data transmission, requiring a separate signal path for each of the bits of a character; internal to computers, this is called a 'parallel bus.'
Research Parallel Transmission
A parallogram is a quadrilateral whose opposite sides are parallel.
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A parallopiped is a rectangular solid figure whose faces are parallelograms.
Research Parallopiped
Paris green is an insecticide based upon the pigment emerald green.
Research Paris Green
In communications systems and computers, parity is a constant state of equality; one of the oldest and simplest methods of error checking data transmission. Characters are forced into parity (total number of marking bits odd or even as selected by choice) by adding a one or zero bit as appropriate when transmitted; parity is then checked as odd or even at the receiver.
Research Parity
A Parity Bit is a check bit appended to an array of binary digits to make the sum of all the digits always odd or always even.
Research Parity Bit
Parity Check is a checking method that determines if the sum of all the digits in an array is odd or even.
Research Parity Check
Parked domain monetization is the business of purchasing world wide web domain names and using them to display advertising on the home page so as to earn revenue from the traffic that accidentally results at the domain. The traffic to these web sites comes from a variety of sources, but is mainly from people miss-typing the name of a well known web site when attempting to access it. At the end of the 20th century, and the start of the 21st century when the world wide web became very popular, unscrupulous individuals realised they could intercept traffic intended for popular web sites by registering variations of the web site's name, and could then display advertising to the unwitting viewers of these web pages. This quickly resulted in many thousands of variations of popular web sites names being registered and directed to single pages containing nothing but advertising.
Research Parked Domain Monetization
A parsec is an astronomical unit of distance equivalent to 3.2616 light-years.
Research Parsec
PASC is an abbreviation for Precision Adaptive Sub-band Coding, and is a digital audio encoding method effectively the same as MPEG layer 1 and was used in Philips now defunct Digital Compact Cassette system. PASC divides the digital signal into equally spaced sub-bands and compresses the data to about 1/4th of the original size)
Research PASC
Pascal is an Algol-descended computer programming language designed by Niklaus Wirth on the CDC 6600 around 1967 as an instructional tool for elementary programming. The language, designed primarily to keep students from shooting themselves in the foot and thus extremely restrictive from a general- purpose-programming point of view, was later promoted as a general-purpose tool and, in fact, became the ancestor of a large family of languages including Modula-2 and Ada.
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In physics, Pascal's principle states that when a fluid completely fills a vessel, and a pressure is applied to it at any part of its surface, that pressure is transmitted equally throughout the whole of the enclosed fluid.
Research Pascal's Principle
In radio terms, passband tuning is a circuit that allows the operator to move the selectivity bandwidth of the receiver above or below the frequency to which the radio is tuned. This is often helpful in reducing interference.
Research Passband Tuning
In Linux computer systems passwd is an ASCII file that contains a list of the system's users and the passwords (in an encrypted format) they must use for access. The /etc/passwd file is comprised of lines, each containing a single entry. Each line has the format:
login name:passwd:UID:GID:user name:directory:shell
Where login name is the name of the user on the system. password is The encrypted optional user password. UID is the numerical user ID. GID is the numerical group ID for this user. user name is the optional comment field (often containing a full username), directory is the user's $HOME directory, shell is the program to run at login (typically if this field is empty the computer will use /bin/sh).
Research Passwd
Password shadowing is a UNIX computer security system where the encrypted password field of /etc/ passwd is replaced with a special token and the encrypted password is stored in a separate file which is not readable by normal system users. On older systems,
password shadowing was often defeated by using a program that made successive calls to getpwent() to obtain the entire password file.
Research Password Shadowing
Pastel colours are colours in which the purity has been reduced by the addition of grey.
Research Pastel Colours
A pawl is a short bar which works in conjunction with a ratchet wheel to prevent backward rotation of the wheel.
Research Pawl
PC Paintbrush by ZSoft is a good drawing program that supports high resolution VGA graphics. It is a full-featured colour-painting program that lets you create and edit freehand illustrations at the pixel level. It supports a wide range of popular scanners allowing scanned images to be imported and edited in black and white, 16 shades of grey, or in colour. Painting elements include boxes, circles, rounded boxes, curves, lines, and text. All of the objects can be sized and filled. The standard painting tools such as a paintbrush, paint roller, eraser, and spray can are available as well as more unique tools such as a colour eraser which lets you erase a single colour in a defined area. When linked to a scanner, a special menu is available that lets you select items to adjust your scanner capabilities. This program lets you paint, scan, and edit images at 300 dpi in colour or with 16 levels of grey. Images can be scanned in and resized without losing picture qualify. PostScript output devices are supported.
Research PC Paintbrush
PC/Focus by Information Builders, Inc. is a complete, fourth-generation language database and information management system for personal computers. Its design, function, and capabilities are identical to its big brother Focus, one of the leading information centre products for IBM or compatible mainframes. Code that is written for one version is easily transported to the another. Since mainframe Focus and PC/Focus share a common language, PC/Focus can be used to prototype mainframe Focus applications. This method is much less time-consuming frees up valuable mainframe resources. PC/Focus supports a menu-driven user interface based on Information Builders Talk Technology which accesses most PC/Focus commands from a menu. The PC/Focus Windows facility lets you incorporate the programs menu interface into customised applications. The scripting or macro language lets programmers store communications procedures that can automatically execute dial-up sequences for accessing remote systems. A screen painter and report generator
make it much easier to design your applications. Database maintenance procedures can be automated by using ModifyTalk which generates procedures based on answers that you give to a series of questions concerning the fields you want to modify. The product supports a SQL Translator which enables the user to type SQL requests against a mainframe Focus database.
Research PC/Focus
pcANYWHERE III is a menu-driven remote control program for IBM PC-compatibles that allows the user to control and/or monitor one PC from another over a communications link. Suitable for support purposes and typically used with standard dial-up modems, pcANYWHERE III connects two PCs so their screens and keyboards are linked as one. Whatever the remote user sees on-screen is also seen on the local screen. pCANYWHERE III includes both host and remote portions necessary for remote connection of two PCs, and is useful for remote connection into networking environments such as Novell NetWare. The package includes a chat mode and call logging feature, and supports programs that require CCA, EGA, MCGA, VGA, and Hercules Graphics.
On the remote PC, pcANYWHERE III runs underneath other applications as a RAM resident program, occupying only 45K of RAM. The local portion runs as a primary task on a PC. The local PC supports any number of remote users and can he programmed with the appropriate telephone numbers and passwords so users can be called by selecting them from a pop-up directory window. The remote computer can be programmed to automatically call the support computer.
Research PCANYWHERE
In audio engineering, PCM (Pulse Code Modulation) is a scheme for encoding audio data as a series of pulses. Each pulse defines a transition from binary one to binary zero.
Research PCM
PCMCIA (Personal Computer Memory Card International Association) is a standard for miniturized laptop expansion cards for modems, storage, and other devices. Often called PC cards.
Research PCMCIA
Pcopy by Patri-Soft is an extension to the DOS computer operating system. Even with DOS 6.0, the DOS copy command can be dangerous to use and has limited options. Pcopy provides abundant options including: Multiple output disks, fill disks efficiently, split files across disks, select files by date/time/size and update/ merge directories. Pcopy includes a special *DISK*.* type wildcard.
Pcopy provides a facility to scan/make directories, prevent accidental file overlays. Pcopy includes both a menu and command line interface.
Research Pcopy
PCShield by Axent Technologies Limited is a good practices enforcing software product for personal computers. It forces users to select passwords which are hard to crack, and provides encryption for data.
Research PCShield
Pdel by Patri-Soft is an extension to the DOS computer operating system. It has extensive file selection capabilities letting you delete just what you want. You can select by date/time, size, attribute and special wildcard patterns like *DISK*.* and mode. You can delete until a specified amount of free space exists. Wipe file data before deleting to prevent file undelete. A test feature simulates delete. Pdel includes an emergency stop by pressing any key.
Research Pdel
The PDP-1 was the first product made by DEC, and was built to demonstrate the feasibility of building a fully-fledged stored-program computer from transistorised digital circuit modules. The PDP-1 was the first machine with random-access core memory to be sold for under $100,000 and was effectively the world's first minicomputer.
Research PDP-1
The PDP-10 (Programmed Data Processor model 10) was a computer that made timesharing real. It was adopted in the mid-1970s by many university computing facilities and research labs, including the MIT AI Lab, Stanford, and CMU. The
PDP-10 was eventually eclipsed by the VAX machines (descendants of the PDP-11) when DEC recognised that the 10 and VAX product lines were competing with each other and decided to concentrate its software development effort on the more profitable VAX. The PDP-10 was finally dropped from DEC's line in 1983, following the failure of the Jupiter Project at DEC to build a viable new model.
Research PDP-10
PDS is an abbreviation for Portable Diagnostic System. It is an expert system which diagnoses faults in machinery from information received from sensors connected to the machinery. Sensor readings are compared with known data about component malfunction symptoms to diagnose faults.
Research PDS
Peat is a fibrous organic compound found in bogs that is formed by the partial decomposition of plants in the acid water of the bog. Peat is a compact, dark brown organic material with a high carbon and represents the first stage in the transformation of vegetation into coal. Peat bogs are distributed throughout the world; extensive deposits are found in North America, Russia, the Scandinavian countries, England, and Ireland. Dried peat, often compressed into briquettes, is used in many European countries, particularly Ireland, as a fuel, although it is not as efficient as coal because of its large content of water and ash. Peat and commercial preparations of partly decayed vegetable matter that are also called peat have excellent moisture-retaining qualities and are used as mulching and soil-improving material for plants.
Research Peat
Pectin is the name given to any of a group of complex carbohydrate derivatives produced in plants.
Pectins are white amorphous substances that yield a viscous solution with water; when combined in the proper proportions with sugar and acids, they form a gelatinous substance that is the thickening agent in fruit jams. Commercial pectin, obtained from apples or lemons, is used in preparing jam from fruits deficient in pectin.
Research Pectin
Pedology is soil science, that is the study of the formation, nature and classification of soil. Modern pedology was founded by the Russian scientist, Dokuchaiev during the late 19th century. The general theory of soils as independant natural bodies was proposed by Dokuchaiev, developed further by Sibirtsev and organised by Glinka. The first international congress of soil science was held in the USA in 1937.
Research Pedology
A pedometer is a device used for estimating the distance travelled on foot by recording the number of steps taken by the bearer of the device.
Research Pedometer
Pegasus Mail is a free, standards-based electronic mail client for IBM PC computers, suitable for use by single or multiple users on single computers or on local area networks.
Pegasus mail is very feature rich, including mail filtering, mail-merge, and the ability to operate multiple-user accounts from one PC. Pegasus Mail can run on single computers using the DOS or Windows operating system, or on local area networks - it has special support for Novell NetWare LANs that allow it to operate intuitively and with almost no maintenance. The program also supports multiple users on a single computer. Versions are available for both 32-bit Windows (Windows 95, 98, NT4 and 2000) and 16-bit Windows (any version of Windows 3.1 or later). Pegasus Mail can act as a complete internal mail system on its own without needing further servers or components: it can send and receive Internet mail on its own using standard protocols (SMTP, IMAP and POP3).
Research Pegasus Mail
The Pelton Wheel is a type of impulse turbine in which specially shaped buckets mounted on the perimeter of a wheel are hit by a fast-flowing jet of water, causing the wheel to turn. The Pelton wheel was invented by the American engineer L A Pelton around 1882.
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A pentadecagon is a fifteen-sided polygon.
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A pentagon is a five-sided polygon.
Research Pentagon
A pentode is an electronic amplifying valve with five main electrodes.
Research Pentode
A pentose is a sugar with five carbon atoms in the molecule.
Research Pentose
A penumbra is a partly shaded region around the shadow of an opaque body. The term is especially applied to describe the partly shaded region around a total eclipse of the sun or moon.
Research Penumbra
Pepper's ghost is a method of producing the illusion of a ghost on the theatrical stage. A large sheet of polished plate glass placed diagonally across the stage acts as a mirror, but at the same time permits objects on the stage to be seen through it. An actor attired to represent the ghost is concealed in the wings and is strongly illuminated. All else surrounding him is painted or draped dull black so that an image of the actor only is formed by the plate glass. The illusion is rendered complete by the fact that light from objects on the stage behind the image causes the ghost to appear transparent. Headless ghosts result simply from enclosing the actor's head in dull black cloth.
Research Pepper's ghost
Perigee is an astronomical term referring to the position in the Moon's orbit nearest to the earth, opposite to Apogee.
Research Perigee
A Perikon Detector was a form of crystal detector employed in the early days of radio broadcasting. It consisted of a crystal of zincite and a crystal of bornite so mounted that there was a point contact between them.
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In chemistry, periodic law is the law that the properties of the elements are periodic functions of their atomic numbers.
Research Periodic law
In chemistry, the periodic table is a table illustrating the periodic system in which the chemical elements are arranged in the order of their atomic numbers are shown in related groups.
Research Periodic table
A periscope or altiscope is an instrument consisting of an arrangement of mirrors in a vertical framework, by means of which a person is enabled to overlook an object (a parapet, for instance) intervening between himself and any view that he desires to see, the picture of the latter being reflected from a higher to a lower mirror, where it is seen by the observer/
Research Periscope
Perl is an interpreted language optimised for scanning arbitrary text files, extracting information from those text files, and printing reports based on that information. It's also a good language for many system management tasks. The language is intended to be practical (easy to use, efficient, complete) rather than beautiful (tiny, elegant, minimal). It combines some of the best features of C, sed, awk, and sh. Expression syntax corresponds quite closely to C expression syntax. Unlike most Unix utilities, Perl does not arbitrarily limit the size of your data - if you've got the memory, Perl can read in an entire file as a single string. Recursion is of unlimited depth. And the hash tables used by associative arrays grow as necessary to prevent degraded performance. Perl uses sophisticated pattern matching techniques to scan large amounts of data very quickly. Although optimised for scanning text, Perl can also deal with binary data, and can make dbm files look like associative arrays.
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 More information about Perl
Permaid is an expert system, developed at Honeywell for trouble shooting large disk drives.
Research Permaid
Permalloy is a nickel steel alloy, containing about 78 percent nickel. It is characterised by a very high permeability in low magnetic fields. It is extensively used in submarine cables.
Research Permalloy
When applied to pigments and stains, the term permanent means fast to light, that is that the pigment will not fade over time due to exposure to light.
Research Permanent
Permanent green is a pigment comprising a mixture of viridian and either cadmium yellow or zinc chrome.
Research Permanent Green
A permanganate is any salt of permanganic acid. Sodium permanganate and potassium permanganate are used for the oxidation of compounds in organic preparations.
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Permanganic acid is a crimson, strongly acid solution used in analysis for the estimation of iron and oxalic acid.
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Perspex is a trade name for polymethyl methacrylate.
Research Perspex
A persulphate is a salt of persulphuric acid. The persulphates have strong oxidizing characteristics useful in industry. Ammonium persulphate was formerly used for reducing the density of photographic negatives.
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Persulphuric acid is obtained from electrolyzing sulphuric acid, and is used for producing persulphates.
Research Persulphuric Acid
A petri dish is a shallow, circular, glass or plastic dish with a loose-fitting cover which is used for cultivaying bacteria and other micro-organisms. It was named after the German bacteriologist J R Petri.
Research Petri Dish
A petrifying liquid is a thin emulsion used instead of water in decorating, when thinning down an oil-bound water paint for exterior use or for use on a very hot surface.
Research Petrifying Liquid
Petrol is a volatile, flammable liquid mixture of hydrocarbons, obtained from
petroleum and used as a fuel for internal-combustion engines.
Research Petrol
Petroleum is an oily, thick, flammable, usually dark coloured liquid that is a form of bitumen or a mixture of various hydrocarbons, occurring naturally in various parts of the world and often separated by distillation into petrol, naphtha, benzene, kerosene and paraffin.
Petroleum was known to the Indians of Western New York, and it was collected in small quantities by them and by the early settlers of New York and Pennsylvania, amounting sometimes to as much as twenty barrels in a year. The first organized and successful effort to bore for petroleum was made in 1854 by a New York company along Oil Creek, New York. Oil was struck at seventy-one feet, and as much as a thousand barrels per day was obtained. Oil fields were quickly located elsewhere in New York and in Pennsylvania, Ohio and West Virginia, those of Pennsylvania proving the richest. The latter yielded 3,000,000 barrels in 1862. Gasolene, naphtha, kerosene, paraffine and other products soon began to be manufactured in the USA from the petroleum.
Research Petroleum
Petroleum refining is the processes used to produce fuels, chemicals, and gas by treatment of petroleum. Petroleum has been known and used for thousands of years, but systematic separation of its components has only been carried out for just over a century. Initially, petroleum was refined almost entirely to produce fuels. Since the Second World War the use of refinery products as a source of petrochemicals has become more important, but over 90 percent of crude petroleum is still used for fuel. The key to petroleum refining is the initial separation of hydrocarbons into various groups of similar compounds. The groups are distinguished by their boiling-points, and they are separated by fractional distillation. A group of hydrocarbons with similar boiling-points is called a fraction. Each fraction has a distinct treatment within the refinery. Fractions for which there is little demand may be converted to other fractions by later refinery processes. Refinery gas is the petroleum fraction with the lowest boiling-point, and does not condense in a fractional distillation column.
Propane and butane may be extracted from refinery gas to make liquefied petroleum gas. The residual gas, containing mainly hydrogen, methane, and ethane, is used as a fuel to operate the refinery. The most economically important product of petroleum refining is the range of fractions called petrol, which boils at 30-140 degrees Celsius. Light petrol condenses at boiling-points of 30-80 degrees Celsius, right at the top of the fractionation column. It is used to make fuel for motor cars and other petrol-engined vehicles. Next down the column, at boiling- points of 80-190 degrees Celsius, naphthas are drawn off. They may be used in blending fuels. Individual naphthas are separated and used to make solvents, and as a raw material in producing many organic chemicals. Much of the naphtha fraction is reformed for use in petrol. The fraction next below the naphthas in the fractionation column condenses at boiling-points of 190-250 degrees Celsius. This fraction contains the kerosenes, which include paraffin, traditionally burnt with a wick for heating and lighting. This fraction is now more important for making aviation fuel for jet aircraft. The final group of fractions condensing in the column is diesel oil, or gas oil, with boiling-points in the range 250-350 degrees Celsius. Their main use is in diesel engines.
Heavier oil which does not evaporate in the initial fractional distillation passes through the bottom of the column. In some refineries these residues pass on to another stage of vacuum distillation. Products separated this way include lubricating oils and petroleum jelly (used as a grease, or as a base for making ointments). Separating individual compounds from the various fractions and residues is done by several methods. Solvent extraction, for example, is another way of extracting lubricating oil from residues. Further solvent treatment can eliminate undesirable contaminants from lubricating oil or kerosenes. Some substances are removed or separated by crystallization, in which the heavier fractions are cooled until waxes crystallize, and other semi-solids solidify. The solid particles are then filtered out. Preparing fractions or products for final use involves many complicated processes. Impurities, of which the most important are sulphur compounds, are generally removed by hydro treatment.
In blending, different fractions are mixed to achieve specific properties. For example, fuel-oils for domestic and industrial heating are a blend of heavy residue oils with lighter fractions which reduce their viscosity. Oils to be burnt in engines generally need fuel additives blended in to improve their performance and safety. Chemical treatment of fractions to change them into other fractions or into feedstocks for petrochemicals is a large and growing part of refinery work. These processes include cracking, in which heavier hydrocarbons in residues are broken down into lighter fractions, particularly petrol. In hydro treatment, unsaturated hydrocarbons may be saturated with hydrogen. To make slightly heavier hydrocarbons, or to turn straight-chain molecules into ring molecules, a reforming process is used. This produces more petrol, and many aromatic hydrocarbons for use in the chemical industry to make explosives, synthetic rubbers, food preservatives, and many other specialist chemicals.
Other building-up processes include polymerisation, in which identical molecules combine, and alkylation, in which hydrocarbon groups or chains are added to molecules. Storage facilities are a vital part of the work of a refinery, which may have hundreds of tanks, generally above ground and about 30 metres in diameter. A huge network of pipes connects the tanks with various processes, so that a tank may be used for storing intermediate fractions, separate compounds, or finished product awaiting transport to users or chemical factories. Large tanks hold the crude oil delivered to the refinery, with each tank used for oil from a particular source. Switching between crude tanks enables selection of the crude to give the properties best suited to the refinery's current workload. Transport of crude to the refinery is by pipeline or by oil tanker (most refineries are near the sea). Transport of finished products is generally by pipeline, road, or rail.
Research Petroleum Refining
Pewter is an alloy of 80 percent tin and 20 percent lead, that ws once much used for making plates and drinking-cups.
Research Pewter
PFS:First Choice by Software Publishing Corporation, is a software package that integrates the power and ease of use of the original pfs: products into one menu-driven product. This product combines spreadsheet, word processing, data management, reporting, communications, and graphics functions into a compact program designed for the beginning or occasional computer user. The First Choice spreadsheet is more intuitive than the spreadsheets in other integrated packages. All entries are typed directly into the cell where they will appear instead of being entered on a command line and then inserted. The Quick Entry key allows automatic entry of a series of related headings such as months of the year. Begin by typing January and then use the Tab key to enter February, March, and April. The First Choice word processor offers a conversion utility that allows quick conversion of files from other popular word processing programs such as Microsoft Word and WordPerfect. Documents created in the word processing module can be viewed or printed as a slide using
custom fonts and styles. You can create on-screen presentations combining both text and graphic charts.
Research PFS:First Choice
Pretty Good Privacy (PGP), from Phil's Pretty Good Software, is a high security cryptographic software application for MS-DOS, Unix, VAX/VMS, and other computers. It uses public-key encryption to protect E-mail and data files. Allowing users to communicate securely with people they have never met, with no secure channels are needed for prior exchange of keys. PGP is well featured and fast, with sophisticated key management, digital signatures, data compression, and good ergonomic design.
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pH (potential of hydrogen) is a measurement of acidity or alkalinity in terms of hydrogen ion content. Pure water has a pH of seven, or neutral. Acids have a pH less than seven, and alkalis a pH greater than seven.
Research PH
In audio engineering phase is the frequency coherence of a signal. If two signals are out of phase, the trough of the first waveform corresponds with the peak of the second, resulting in cancellation.
Research Phase
Phase modulation is a radio modulation technique similar to FM, that varies the carrier frequency of a transmitter in accordance with the strength and frequency of the modulating signal.
Research Phase Modulation
Phenol formaldehyde resins (phenol resins or PF resins) are materials produced by the interaction of phenol and formaldehyde under a variety of conditions and were the first synthetic resins made on a large scale.
Research Phenol Formaldehyde Resins
Phenolphthalein is a derivative of triphenyl-methane, formed when phthalic acid is heated with phenol in the presence of a dehydrating agent. It is a pale yellow solid that is soluble in alcohol, and forms bright red compounds with alkalis, that are decomposed by the weaker acids - even carbon dioxide. On account of this it is used as an indicator in acidimetry.
Research Phenolphthalein
Phenyl benzene is a colourless crystalline organic compound. It can be made by passing benzene through a red-hot tube, when condensation takes place with the formation of
phenyl benzene. It also occurs in coal-tar, and it is used in organic syntheses.
Research Phenyl benzene
The Philips D2999 was a General coverage portable communications receiver manufactured between 1986 and 1989 and providing coverage from 150 khz to 30 Mhz in AM and SSB modes plus the VHF broadcast band in FM mode. The D2999 was aimed more at the domestic market than the amateur radio enthusiast, and as such made up for what it lacked in performance in audio quality.
Research Philips D2999
Philology is the branch of knowledge that deals with the structure, historical development, and relationships of a language or languages. Some one who studies philology or is an authority on philology is known as a philologist.
Research Philology
The phon is the unit of loudness.
Research Phon
A phono plug is a type of coaxial push-on connector, especially used in audio equipment.
Research Phono Plug
The phonograph was a device invented by Thomas Edison in 1877 for recording and reproducing sounds upon tin foil. The phonograph consisted of a grooved cylinder, covered with tin foil. The cyclinder was revolved and slowly moved endways by means of turning a handle. On each side of the cylinder was a recorder with a diaphragm and needle which indented the foil in response to the sound vibrations received. The phonograph was the fore-runner of the gramaphone
Research Phonograph
Phosgene is a colourless, fuming toxic gas formed by the union of carbon monoxide and chlorine in sunlight, or by the oxidation of chloroform by sulphuric acid and potassium bichromate. It is decomposed by water.
Research Phosgene
A phosphate is any salt of phosphorus oxy acids.
Research Phosphate
Phosphating is the name of various processes used to increase the corrosion resistance of bright sheet steel, such as used in the motor car industry.
Research Phosphating
Phosphoric acid can exist as a crystal or clear liquid. It is an oily, thick, colourless, and odourless liquid, or a thick, colourless, unstable crystalline solid. It is used in the manufacture of phosphates, such as salts, soaps, and detergents; fertilizers; yeasts; fire control agents; opal glass; electric lights; dental cements; waxes and polishes; gelatin; ethylbenzene, propylene, and cumene; and soft drinks. It is used as an acid catalyst, soil stabilizer, antioxidant in food, acidulant and flavour agent in jellies and preserves, bonding agent for refractory bricks, and petrol additive. It is also used in the rust proofing and polishing of metals, cotton dyeing, tile cleaning, extracting penicillin, hot stripping for aluminium and zinc substrates, ceramic binding, water treatment, process engraving, electro-polishing, coagulating of rubber latex, operating lithography and photoengraving operations, and pickling. It is used to manufacture the phosphoric acid electrolyte fuel cell system which has created the largest fuel cell built and has been used to treat lead poisoning.
Phosphoric acid is incompatible with strong caustics and most metals. It readily reacts with metals to form flammable hydrogen gas. The liquid can solidify at temperatures below 21 degrees C. It is corrosive to ferrous metals and alloys. It is soluble in alcohol and hot water. It can form three series of salts: primary phosphates, dibasic phosphates, and tribasic phosphates. It is deliquescent and hygroscopic. It is a chelating agent. It has a low vapour pressure at room temperature. Phosphoric acid is also known as orthophosphoric acid, metaphosphoric acid, and white phosphoric acid.
Research Phosphoric acid
Phosphorus is a non-metallic element of the nitrogen family that occurs widely as a phosphate. It has the symbol P.
Phosphorus is an essential ingredient of all living things, and is present in well-marked amounts in nervous tissue and bones, composing in combination, as calcium phosphate, about 17 percent of the ash of bone. Ordinary phosphorus is a waxy solid that is colourless when pure, and forms brilliant, highly refractive crystals when sublimed in a vacuum, though usually it is more or less coloured pale yellow or buff from the action of light or the presence of impurities. It is practically insoluble in water, but dissolves freely in carbon disulphide and sulphur chloride, being also soluble, though to a lesser extent, in chloroform, aniline, and oils.
Phosphorus is most marked chemically by the readiness with which it is oxidized: thus, it glows and gives off fumes of a garlic odour when exposed to the air, and this reactions often generate enough heat to ignite the sample. When ignited in the open air phosphorus burns with a dazzling white light, forming a snowy deposit of phosphoric anhydride.
Research Phosphorus
Phosphorus acid is a powerful reducing agent. It is formed by acting on phosphorus trichloride with water or hydrochloric acid, and cab be obtained crystalline by evaporating the solution. It behaves as a dibasic avid, and is decomposed on heating, giving off spontaneously inflammable phosphine and forming metaphosphoric acid.
Research Phosphorus Acid
A phot is a unit of luminous flux equal to the illumination produced by one lumen on a surface of one square centimetre.
Research Phot
Photography is the art, and sometimes business, of taking and also sometimes producing and printing photographs.
Early cameras operated upon the principle of allowing light reflected from a subject to fall upon a light-sensitive chemical impregnated plate, later plastic film. These plates or films were then treated with other chemicals to prevent further sensitivity to light, thereby fixing the image which was then printed. Later digital cameras evolved which used electronic light sensors to record the image in a binary digital file on a memory card.
If too much light is allowed in to the camera, the picture will be over exposed, and will look bright and indistinct. If not enough light is allowed in, the picture will be under exposed and will look dark and indistinct. It is less common for photographs to be over exposed, than under exposed.
Light is allowed in to the camera to the photograph plate, film or sensor through a quickly opening and closing door called the shutter. The size of the hole which is revealed by the shutter is known as the aperture, and is measured in F-Stops, such as F1.8, F4.5, F11 etc. Where, confusingly, the larger the F number the smaller the aperture is. Thus, F1.8 is quite a large aperture, and F11 is fairly small. A larger aperture, represented by a smaller F number, lets in more light than a smaller aperture.
The length of time for which the shutter remains open, letting light in through the aperture is often referred to as the shutter speed, and is measured in fractions of a second. Thus, a shutter speed of 500 implies that the aperture will be open for 1/500th of a second, while a shutter speed of 125 implies that the aperture will be open for 1/125th of a second. The longer the aperture remains open, the more light will enter.
How quickly the photographic plate, film or sensor reacts to the light reaching it through the aperture is known as the sensitivity of the plate, film or sensor and is measured in ISO or ASA units. The larger the ISO value, the quicker the plate, film or sensor will react to the light. Thus, a sensitivity of ASA or ISO 100 will react slower than a sensitivity of 200 or 400.
The aperture size, shutter speed and sensitivity, work together to determine the level of exposure that occurs when a picture is taken. Automatic camera settings will set these three values for you, so that the picture is properly exposed, and if it can not be properly exposed, will warn you. However, there are other effects connected with each of these three settings.
The higher the sensitivity of the photographic plate, film or sensor, the more grainy or noisy the photograph will be. Therefore, using the lowest possible sensitivity will give the best possible quality for the photograph. In order to use a low sensitivity, the subject must be as brightly lit as possible. For example a subject in bright sunshine or lit by powerful lamps or the use of a camera flash gun.
The camera's aperture size governs the depth of the photograph. The smaller the aperture is, the deeper the field of focus. Using a large aperture size will result in only the subject being in focus, objects behind and in front of the subject will be blurred. Using a small aperture will allow objects behind and in front of the subject to also be in focus. The smaller the aperture size, the further behind and in front of the subject objects will remain in focus, and by extension the easier it will be to focus upon the subject.
The most noticeable effect of the shutter speed is in reducing motion blur and camera shake. When holding a camera, particularly one with a long lens every one will quiver their hand to a greater or lesser degree. When using a zoom lens, this quivering or camera shake is much more noticeable than when using a shorter or wider angle lens. If the camera is moved, even slightly while the shutter is open, the picture will be blurred. The more the camera moves while the shutter is open, the more blurring will occur. By using a fast shutter speed, the shutter is open for less time and as such less movement affect the photograph. Similarly, if the subject being photographed moves while the image is being taken, the resulting photograph will be blurred. Using a fast shutter speed of 1/500th of a second or faster enables photographs to be taken of action shots, such as footballers in mid-movement or in the air while heading the ball. The subject's movement being slower than the speed of the shutter opening and closing which appears to freeze the moment in time.
The best way to reduce camera shake is to use a tripod. If you can not use a tripod, try resting the camera on a firm surface, such as a wall, fence post or tree. It can not be over emphasised that using a tripod will result in better photographs as every one quivers ever so slightly when taking photographs. Even activating the shutter release on the camera can slightly jar the camera. To overcome this, many photographers use a camera with automatic frame advance or sequential shooting, whereby after activating the shutter release the camera takes multiple photographs until the shutter release mechanism is released. In this way, three images may be taken automatically, the first and last will often suffer from slight camera shake due to the action of operating the shutter release mechanism, while the second image will not.
Research Photography
In physics, photometry is the measurement of the luminous intensity of a light source, or the amount of luminous flux falling upon a surface from such a source. Photometry is important in photography , astronomy, and illumination engineering. Instruments used for photometry are called photometers. Light waves stimulate the human eye in different degrees, depending on the wavelength of the light. Because it is difficult to make an instrument with the same sensitivity for different wavelengths as the human eye, many photometers use a human observer. Photoelectric photometers need special collared filters to make them respond like the human eye. Instruments that measure radiant energy instead of light are called radiometers, and must be made equally sensitive to all wavelengths. The intensity of a light source is measured in candle power, usually by comparing the source with a standard source provided by the National Bureau of Standards. The known and unknown sources illuminate portions of a window surface side by side, and their distances are adjusted until the illumination on the surface is the same. The relative intensity is then calculated from the inverse square law.
Research Photometry
A photon is a light quantum, that is a definite amount of radiation having a frequency within the visible spectrum. A photon is emitted from an excited atom when one of the orbital electrons, having been transferred to an orbit of higher energy level, suddenly returns to its former orbit.
Research Photon
The photophone was an instrument invented by Graham Bell and Sumner Tainter, by which sounds, including speech, could be transmitted to a distance by the agency of light. A powerful beam of light was made to fall on a very thin glass mirror, which formed a diaphragm in a bell-shaped receiver. The light was reflected from the mirror through a lens, by which the rays were rendered parallel, and then passed to the distant station. At this point the beam was received in a parabolic mirror and concentrated on a cell composed of alternate layers of brass and selenium, which was placed in series with a battery and telephone reveiver, and which had the property of diminishing in resistance when light fell on it (it was photosensitive). Sound waves were modulated with the light by coming into contact with the mirror causing it to distort and the light rays transmitted also accordingly.
Research Photophone
Adobe Photoshop is a high-end image editor originally for the Macintosh computer, but later ported to the PC under the Windows operating system. The primary strength of Photoshop comes from it's layers which enable elements of an image to be manipulated independantly of the others, a feature which was quickly copied by other lower cost image editors.
Research Photoshop
Something which is phototropic seeks light. The term is used in Biology to describe animalcules which seek the light.
Research Phototropic
Phthalic Acid is obtained by the oxidation of napthalene by means of fuming sulphuric acid and mercury. It forms colourless crystals that are soluble in water. When heated it yields an anhydride and is the parent substance of the phthalein dye-stuffs.
Research Phthalic Acid
In chemistry, physical change is a change in the condition or state of a substance; it's composition is not altered.
Research Physical change
Physiognomy is the judging of nature and character of animals and people from external appearances. It is an ancient art, which was remodelled along broadly scientific lines by Charles Dawrwin in his book 'Expression of Emotions in Man and Animals' published in 1873. Formerly, criminology, pathology and anthropology all made extensive reliance on physiognomy, but in the later part of the 20th century it was widely discredited as a science.
Research Physiognomy
Picric acid (Carbazoilic acid) or trinitro-phenol is a lemon yellow, crystalline acid, prepared by the action of nitric and sulphuric acids on phenol. It is used for dyeing silk goods after mordanting with alum. It is also used for imparting a bitter taste to beer, and as an explosive either in the form of the free acid or in one of its salts. Most of these explode violently on percussion or on detonation, and when consolidated by fusion, it is used as a high explosive for charging shells under the name lyddite. It yields explosive salts by the substitution of metals for the hydrogen of the hydroxyl group.
Research Picric Acid
Pikecrete is a compound, invented by a British scientist named Pike during the Second World War, comprised of 14% sawdust or wood pulp, and 86% water mixed thoroughly and frozen. The resulting compound is not only extremely strong, but also resists melting and is less dense than water. Winston Churchill planned during the Second World War to build an aircraft carrier out of pikecrete. The resulting platform would have been solid and as such resistant to bullets and torpedoes (it couldn't be 'holed' like a traditional ship) and with its thermodynamic properties would have not melted even in tropical seas for quite a long time.
Research Pikecrete
Pinchbeck (also known as bath metal, Dutch gold, Dutch metal) is an alloy of 80 percent copper and 20 percent zinc once used for making cheap watch cases where it was intended to imitate gold, and more recently as a substitute for the more expensive bronze. It was invented by a London watchmaker in the 18th century.
Research Pinchbeck
Pine is a UNIX based email system, based on Elm but with improvements which include a built-in text editor and address book.
Research Pine
Pinene is a terpene colourless liquid which smells like turpentine and occurs in pine trees and the essential oils of eucalyptus, lemon and thyme.
Research Pinene
Piperidine is a secondary amine, occurring in combination with piperic acid in pepper.
Research Piperidine
Piperine is an alkaloid occurring in pepper. It is a feeble base that crystallises in prisms, and colours sulphuric acid red.
Research Piperine
A pipette is a tube open at both ends, used for accurately measuring off small quantities of liquids. A pipette may be straight, or provided with a bulb, and is constricted at the mouth to a narrow orifice. In using a pipette the liquid is sucked up to a little above the mark, the top of the tube closed with the finger, of which the pressure is relaxed until the liquid falls to the mark, when the flow is stopped by increasing the pressure again. The measured quantity of liquid is then allowed to flow out into the required vessel.
Research Pipette
In computing a pixel is one of the dots which comprises a display or print. Resolution is often described in terms of pixels, or as dots per inch, such as '800x600' meaning 800 pixels wide by 600 pixels deep or '72 dpi' meaning 72 dots-per-inch.
Research Pixel
A plane table is a device used in surveying and consisting of a movable telescope resting upon a flat board mounted on a tripod. By its use a reliable plan may be prepared in the field directly upon a sheet of paper pinned to the board.
Research Plane table
Plaster of paris is a form of hemhydrate plaster derived from rock gypsum crushed and heated to a temperature of 170 degrees celsius. This process removes some 75 percent of the water in the plaster, which when mixed with water sets (hydrates) very quickly.
Research Plaster of Paris
Plastic is a group of synthetic polymers made from oils and which are capable of being moulded into shape by heat or pressure or both.
Research Plastic
Plexiglas is a trade name for polymethyl methacrylate.
Research Plexiglas
Pliers are a type of small pinchers with long jaws, used for bending and cutting metal rods or wire, and for handling small objects - though not as small as one might use tweezers for - such as the parts of a watch, small screws and the like.
Research Pliers
Plink86 Plus by Phoenix Computer Products is an overlay linker that brings modular programming to the PC. It lets you write a program as large and complex as necessary with no need to worry about whether it will fit within available memory. Plink86 Plus's automatic overlay-module technique allows programs to be divided into any number of tree-structured overlay areas, handles diskette changes, and segments the program for add-on packages. Plink86 Plus is a two-pass linkage editor that accepts any object file conforming to the Intel or Microsoft format and outputs executable program files. The first pass is for memory-segment addressing and the second creates the output file. Plink86 Plus works with Lattice C, Microsoft FORTRAN, Microsoft C 5.0, IBM FORTRAN (77), the IBM BASIC Compiler, the Turbo C compiler, and Clipper among other compilers.
Research Plink86 Plus
A plough is an agricultural implement comprising one or more cutting blades mounted in a frame which is drawn by draught animals such as a horse or ox, or by a tractor, and is used for tilling the soil, that is cutting furrows in it and turning it up in readiness for sowing.
Research Plough
A ploughfoot was an adjustable staff that was formerly attached to the beam of a plough to enable the ploughman to determine the depth of the furrow he was making.
Research Ploughfoot
Plutonium is a radioactive metal element with the symbol Pu. It was discovered by the chemists Glenn Seaborg and Edwin McMillan in 1940. The isotopes of plutonium were first prepared and studied by Seaborg and his associates in 1941. Trace amounts of the element have since been found in uranium ores, but plutonium is prepared in relatively large quantities today in nuclear reactors. Chemically, plutonium is reactive, its properties somewhat resembling those of the rare earth elements. The silvery metal, which becomes slightly yellow through oxidation caused by exposure to air, exists in six varying crystalline forms and has four different oxidation states. The metal gives off heat because of its radioactivity ; 15 different isotopes of
plutonium, ranging in mass number from 232 to 246, are known.
Plutonium-239 has a half-life of 24,360 years, and is produced by bombarding uranium-238 with slow neutrons. This forms neptunium-239, which in turn emits a beta particle and forms plutonium-239.
Plutonium is the most economically important of the transuranium elements because plutonium-239 readily undergoes fission and can be both used and produced in quantity in nuclear reactors. It is also used in making nuclear weapons. It is an extremely hazardous poison due to its high radioactivity. Plutonium-238 has been used to power equipment on the moon by means of the heat it emits.
Research Plutonium
PointCast Network is a free computer program for the IBM PC. It is the Internet news network that appears instantly on your computer screen, with headlines that run dynamically across the screen. All you have to do is click on an item for detailed information. PointCast broadcasts national and international news, stock information, industry updates, weather from around the globe, and sports scores.
Research PointCast Network
Polonium is a metal radioactive element with the symbol Po.
Research Polonium
Polyamide is a large class of polymers in which the units are linked by an amide group. Polyamides have a high lubricity and moderate strength. They are tough, inexpensive to produce, but have poor dimensional stability due to their tendancy for water absorption. Polyamides are used to make bearings, blow mouldings, and clothing fabric. The synthetic resin nylon is a classic example of a polyamide.
Research Polyamide
Polycarbonate is a thermoplastic polycondensate polymer mass-produced since 1958. It has excellent strength and possesses good dimensional stability, dielectric strength, flame retardancy, and an impact resistance which is the highest among current transparent rigid materials. It is difficult to machine, however.
Research Polycarbonate
Polychlorinated biphenyls (PCBs) are a family of man-made chemicals that contain 209 individual compounds with varying toxicity. Commercial formulations of PCBs enter the environment as mixtures consisting of a variety of PCBs and impurities. Because of their insulating and non-flammable properties, PCBs have been used widely as coolants and lubricants in transformers, capacitors, and other electrical equipment. The manufacture of PCBs stopped in the USA in October 1977 because of evidence that PCBs accumulate in the environment and may cause health hazards for humans.
Research Polychlorinated biphenyls
Polycyclic aromatic hydrocarbons (PAHs) are a group of chemicals that are formed during the incomplete burning of coal, oil and gas, garbage, or other organic substances. PAHs can be man-made or occur naturally. There is no known use for most of these chemicals except for research purposes. A few of the PAHs are used in medicines and to make dyes, plastics, and pesticides. They are found throughout the environment in the air, water, and soil. There are more than 100 different PAH compounds. Although the health effects of the individual PAHs are not exactly alike, the following 15 PAHs are considered as a group: acenaphthene, acenaphthylene, anthracene, benz(a)anthracene, benzo(a)pyrene, benzo(b)fluoranthene, benzo(ghi)perylene, benzo(k)fluoranthene, chrysene, dibenz(a,h)anthracene, fluoranthene, fluorene, indeno(1,2, 3-cd)pyrene, phenanthrene, pyrene. As pure chemicals, PAHs generally exist as colourless, white, or pale yellow-green solids.
Most PAHs do not occur alone in the environment (including those found at hazardous waste sites), rather they are found as mixtures of two or more PAHs. They can occur in the air either attached to dust particles, or in soil or sediment as solids. They can also be found in substances such as crude oil, coal, coal tar pitch, creosote, and road and roofing tar. Most PAHs do not dissolve easily in water, but some PAHs readily evaporate into the air. PAHs generally do not burn easily and they will last in the environment for months to years.
Research Polycyclic aromatic hydrocarbons
Polyester is a thermosetting plastic used in the manufacture of synthetic fabrics since 1942. Polyester exhibits excellent dimensional stability but a low resistance to acids and bases.
Research Polyester
Polyethylene is a thermosetting plastic polymer of ethylene mass produced since 1939. It is an inexpensive plastic widely used in the manufacture of plastic bags, beverage bottles and extruded pipe. Polythene is a proprietory name for polyethylene made by one manufacturer.
Research Polyethylene
A polymer is a compound made up of large molecules composed of many repeated simple units.
Research Polymer
Polymethyl methacrylate or acrylic, is a rigid, glassy thermoplastic with a good weight-to-strength ratio and resistance to moisture. Polymethyl methacrylate is used in the manufacture of optical devices, glazing, aircraft windows and similar. As a synthetic fibre, polymethyl methacrylate is often used as a substitute for wool. It was first launched commercially in 1947 but not produced in any great volume until the 1950s. It is a strong, warm fabric that drapes well. It is used to make sweaters and tracksuits, and is also made into linings for boots, gloves, jackets and slippers. Common tradenames for acrylic fibre are Acrilan and Orlon.
Research Polymethyl Methacrylate
A polysaccharide is a long chain of carbohydrate made up of hundreds of linked simple sugars, such as glucose.
Research Polysaccharide
Polystyrene is a thermoplastic polymer mass-produced since 1930. Polystyrene is easy to mould, it is inexpensive, machines well, and possesses excellent transparency, but is structually weak. It is used to manufacture inexpensive packaging materials, especially when expanded (styrofoam), and in the manufacture of low cost consumer plastic items such as pens and safety razors, CD jewel cases &c.
Research Polystyrene
Polytetrafluorethylene (PTFE) is a slippery theromplastic polymer with similar properties to polystyrene, except that it has a very wide temperature range and cannot be practically melted. It is chemically inert and as such is resistant to adhesives. Polytetrafluorethylene is used for making gaskets, hoses, insulators, bearings, and for coating metal surfaces in chemical plants and in non-stick cooking vessels - often under the tradename Teflon.
Research Polytetrafluorethylene
Polyvinyl acetate (PVA) is a thermoplastic vinyl polymer formed by the co-polymerization of vinyl chloride and vinyl ethanoate. Polyvinyl acetate is resistant to oil and some chemicals and is widely used to produce plastic sheets, hoses and belts and as a water-based emulsion as an adhesive - 'PVA Glue'.
Research Polyvinyl Acetate
Polyvinyl chloride (PVC) is a thermoplastic vinyl polymer mass-produced since 1938. It is an inexpensive plastic with high dielectric strength, outdoor stability, chemical resistance and good moisture stability but a poor resistance to heat. It is widely used in the manufacture of low-cost imitation leather clothing - particularly 'fetish' wear - and in wire and cable insulations.
Research Polyvinyl Chloride
Ponceau 4R (E124) is a red synthetic azo dye used in the UK as a food colouring, but banned in the USA and Norway. Ponceau 4R has been found to cause hyperactivity in children and also allergic reactions.
Research Ponceau 4R
In telecommunications, POP (Point of Presence) is a local dial-in point for an Internet Service Provider.
Research POP
In computing a port is an 8-bit wide interface between the processor and another system hardware device. In a Personal Computer, each hardware device makes use of a range of port addresses and as such conflicts can occur when two devices use port addresses which overlap.
Research Port
Portland cement is the essential constituent in concrete, cement rendering and formerly in asbestos-cement sheeting. Portland cement is produced by burning limestone with clay or shale at a high temperature until it forms a clinkered mass, which is then cooled and ground into a fine powder.
Research Portland Cement
A positron is a positively-charged particle of the same mass as the electron and with a charge equivalent but opposite in sign to that of the electron.
Research Positron
Postcode, from AFD Software, is a software system which looks up addresses from
postcodes. The data file is about 18Mb, which includes the indices which reduce typical search times to less than one second.
Research Postcode
PostScript was a groundbreaking Page Description Language (PDL), based on work originally done by John Gaffney at Evans and Sutherland in 1976, evolving through 'JaM' ('John and Martin', Martin Newell) at XEROX PARC, and finally implemented in its current form by John Warnock et al. after he and Chuck Geschke founded Adobe Systems Incorporated in 1982. PostScript gets its leverage by using a full programming language, rather than a series of low-level escape sequences, to describe an image to be printed on a laser printer or other output device (in this it parallels EMACS, which exploited a similar insight about editing tasks). It is also noteworthy for implementing on-the fly rasterisation, from Bezier curve descriptions, of high-quality fonts at low (e.g. 300 dpi) resolution (it was formerly believed that hand-tuned bitmap fonts were required for this task).
Research Postscript
Pot Metal is an inferior kind of brass comprised of 10 parts of copper to 6 or 8 parts of lead. It is used for making large vessels employed in the arts and in some stained glass.
Research Pot Metal
Potassium is a silver-white, light, soft, low-melting, univalent metallic element of the alkali group, it occurs abundantly in nature especially combined in minerals. It has the symbol K.
Research Potassium
Potassium antimonyl tartrate (tartar emetic) is a poison formerly used in small quantities to induce sweating and as an emetic. It is obtained by boiling antimony oxide with a solution of cream of tartar. It forms rhombic efflorescent crystals, is fairly soluble in water and has an unpleasant taste.
Research Potassium antimonyl tartrate
Potassium benzoate is a chemical antimicrobial (it kills mold, yeast and bacteria) used as a food preservative, especially as an alternative to sodium benzoate where a lower sodium content is required. Potassium benzoate is a white coloured, granulated solid, almost odourless, which dissolves readily in water and has a tangy taste.
Research Potassium Benzoate
Potassium bisulphate (potassium acid sulphate) is a colourless, crystalline water-soluble substance used chiefly in the conversion of tartrates to bitartrates.
Research Potassium Bisulphate
Potassium bromate is a white, crystalline, water-soluble powder used chiefly as an oxidising agent and as an analytical reagent.
Research Potassium Bromate
Potassium bromide (bromide) is a white, crystalline, water-soluble powder. It has a bitter, saline taste and is used in the manufacture of photographic papers and plates and as a sedative.
Research Potassium Bromide
Potassium carbonate is a white, granular, water-soluble substance used chiefly in the manufacture of soap, glass and potassium salts.
Research Potassium Carbonate
Potassium nitrate is a white bitter tasting substance used in gunpowder, as an oxidising agent, for pickling meat and in medicine.
Research Potassium nitrate
Potassium oxalate is a colourless, crystalline water-soluble substance. It is toxic, and is used as a bleaching agent and in medical tests as an anticoagulant.
Research Potassium Oxalate
Potassium sorbate is a potassium salt version of sorbic acid, a polyunsaturated fat used to inhibit mould growth. It was first discovered by the French in the 1850's, having been derived from the rowan tree. It is widely used in the food industry. It has been found to be non-toxic even when taken in large quantities, and breaks down in the body into water and carbon dioxide in the Kreb's Cycle.
Research Potassium Sorbate
Potassium Thiocyanide is a sulphocyanate. It is colourless, easily dissolvable crystals used in dyeing.
Research Potassium Thiocyanide
Potential energy is the energy something has by reason of its position or state.
Research Potential Energy
The poundal is the imperial unit of force, now replaced in the SI system by the newton. One poundal equals 0. 1383 newtons. It is defined as the force necessary to accelerate a mass of one pound by one foot per second per second.
Research Poundal
In physics, power is defined at the rate of doing work, and is expressed by the equation: Average
Power = Work done/Time taken.
Research Power
The Powernote MMX is a laptop PC from Powercom. It is based upon an Intel Pentium MMX processor clocked at 166 Mhz and is supplied with 32 mb of RAM, 810 mb EIDE hard disk, CD-ROM, 1.44 mb floppy drive and a Neomagic 2093ZV graphics accelerator.
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Microsoft PowerPoint is one of the most useful presentation programs available. Its unique approach gives you the ability to create overheads, 35mm slides, notes for yourself, and handouts for your audience. PowerPoint lets you plan, compose, and create an entire presentation in a simple, structured manner. PowerPoint lets you create, manage, edit, and manipulate slides. Powerful word processing capabilities and some drawing capabilities are built into the program. The product lets you integrate elements created elsewhere. When creating presentations using the Slide Master, you can create a standard format template, including text and graphics, for all slides. Free-form design lets you integrate what you need on a slide including typeset-quality text, diagrams, graphs, and illustrations. Graphics from the clipboard or scrapbook can be integrated into a PowerPoint slide or you can use the Paste From command to import information from files of other applications. The program's text capabilities include multiple fonts, sizes, and styles.
Powerpoint also includes a spell checker and a find-and-replace text command that works with slides, note pages, and handout pages. You can also create diagrams with its drawing tools which include lines, ellipses, rectangles, and rounded rectangles. The slide-management tools let you rearrange and refine your presentation. A slide sorter displays your slide show on-screen in thumbnail sketch view. You can delete, copy, and rearrange slides and add slides from other presentations. You can also edit the slides by double clicking on them. A slide show feature lets you preview your slides in sequence if you want to rehearse your presentation. Speaker's notes and audience handouts (with two, three, or six slides per page) can be created at the same time you create slides through a user-definable notepage associated with each slide. You can output slides to a printer, slide-making device, or the Genigraphics slide making bureau (a driver is included).
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Praseodymium is a metal element with the symbol Pr used as a pigment in glass.
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In chemistry, a precipitate is an insoluble liquid that separates from solution.
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A preserving jar is a glass jar covered with a glass cap seated on a flat rubber ring used for keeping fruit in an eatable condition for a long time. Clean fruit and water are placed in the jar, leaving a small air space at the top. Several of these jars are placed in a large vessel of cold water, which is then slowly brought to the boil. During this process the glass caps with their rubber rings are loosely held in position by a metal screw cap. About 10 minutes boiling is generally sufficient to sterilise the fruit and to cause air to be driven from the jars by steam from the water inside. The screw caps are then tightened and the jars removed from the water. After cooling, the space at the top of the jars contains only water vapour at low pressure. As a result, the glass cap is then firmly pressed down by atmospheric pressure. No bacteria-laden air can afterwards enter, and so the contents remain in good condition for a long period. When the jars have cooled the presence of the metal cap is not strictly necessary, as the seal is
now maintained by atmospheric pressure.
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In physics, pressure is defined as: The force acting normally (perpendicularly) per unit area.
Pressure can be represented by the equation: Pressure = Thrust / Area. Thus, given an object of a static weight, the pressure exterted by that object varies with the area to which the pressure is applied. For example, a brick exters less pressure upon an area when lying on its large side than when standing on its small end.
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A primary colour is one of the three basic lights of red, green and blue. A primary pigment is one of the three basic pigment colours of red, yellow and blue. From the mixing of these three colours different colours can be produced, though it should be strongly noted that mixing different colours of light will produce a different colour than is produced from mixing the same coloured pigments, for example mixing the three primary coloured lights in equal proportions will produce a white light, while mixing the same three coloured pigments in the same proportions will produce a black pigment.
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Prince's Metal (or Prince Rupert's Metal) is imitation gold made from copper and zinc.
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A prism is a solid figure that is essentially triangular in shape and made of a transparent material. They are used in physics to deviate or disperse a ray in optical instruments or laboratory experiments. If a narrow beam of white light is passed through a prism it is split into a range of colours. The light is split because each of the colours is refracted by a different amount, because each is light of a different wavelength.
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In Unix, proc is a pseudo-filesystem that is used as an interface to kernel data structures rather than reading and interpreting /dev/kmem. In particular, its files do not take disk space.
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Provess white is an opaque water-mixed white prepared from blanc fixe and used by designers and commercial artists.
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Procomm is a shareware communications program for the IBM PC usually used for accessing dial-up services such as BBS.
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In radio, a product detector is a beat frequency oscillator with enhancements for improved SSB and CW reception.
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Prolog is a computer programming language used mainly for artificial intelligence.
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Promethium is a metal element with the symbol Pm.
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Propane is a gaseous hydrocarbon found in petroleum. It has the formulae c3h8.
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Proportional Compasses are compasses used for reducing or enlarging drawings, having the legs crossing so as to present a pair on each side of a common pivot. By means of a slit in the legs, and the movable pivot, the relative distances between the points at the respective ends may be adjusted at pleasure in the required proportion.
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Propyl gallate (n-propyl ester of 3,4,5-trihydroxybenzoic acid) is a white to creamy-white coloured, crystalline, odourless solid, soluble in water, ethanol and fat, with a slightly bitter taste, used as an anti-oxidant in processed foods.
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Propylene glycol is a colourless viscous hydroscopic sweet-tasting compound used as an antifreeze and brake fluid, and in some cosmetics. It is also known as 1,2-dihydroxypropane.
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Propylene glycol monomethyl ether is a glycol ether primarily used in the manufacture of lacquers and paints, as an anti-freeze in industrial engines, a tailing agent for inks used on very high-speed presses, a coupling agent for resins and dyes in water-based inks, and a solvent for celluloses, acrylics, dyes, inks, and stains. It is also used in cleaning products such as glass and rug cleaners, carbon and grease removers, and paint and varnish removers; and in pesticide formulations as a solvent for applications to crops and animals.
Propylene glycol monomethyl ether is a colourless liquid with a sweet ether-like odour and bitter taste. It is soluble in water, ether, acetone, and benzene. It is also known as 1-methyl-2-hydroxypropane.
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Propylene oxide is a colourless liquid with an ether-like odour that is used mainly as a chemical intermediate in the production of polyurethane polyols, which are used to make polyurethane foams, coatings, and adhesives. It is used in the manufacture of propylene glycol, which is used in fibreglass-reinforced plastics, foods, cosmetics, pharmaceuticals, cigarette tobacco, packaging materials, dyes, and hydraulic fluids. It is also used in the preparation of glycol ethers, dipropylene glycol, industrial polyglycols, lubricants, surfactants, oil demulsifiers, isopropanolamines, and as a solvent and soil sterilant. It is used in fumigation chambers for the sterilization of packaged foods; as a stabilizer for methylene chloride, fuel, and heating oils; in treating wood for termite resistance; as an acid scavenger and pH control agent; for removing residual catalysts from crude polyolefins; in fuel-air explosives in munitions; and as a component of Zeospan, a polyether rubber. Propylene oxide is a volatile, flammable liquid
that is soluble in water, alcohol, and ether. It is highly dangerous when exposed to heat or flame. It has a violent reaction with hydrogen chloride, chlorosulphonic acid, hydrogen fluoride, and oleum. It should not be stored in the presence of acids, bases, chlorides of iron, aluminum, and tin, or peroxides of iron and aluminum; any of these may cause violent polymerization.
Propylene oxide is miscible with most organic solvents, and forms a two-layer system with water. It is incompatible with anhydrous metal chlorides, iron, strong acids, caustics, and peroxides, and reacts vigorously with oxidizing materials. When exposed to flame, propylene oxide can explode. Polymerization may occur due to high temperatures or contamination with alkalis, aqueous acids, amines, and acidic alcohols.
Propylene oxide is also known as epoxypropane; 1,2-epoxypropane; methyl ethylene oxide; methyl oxirane; propene oxide; and 1,2-propylene oxide. Derivatives of
propylene oxide are polyether polyols; propylene glycol; di- and tripropylene glycol; poly (propylene glycol)s; surfactants; glycol ethers; and isopropanolamines.
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Protactinium is a rare actinide element with the symbol Pa.
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In Personal Computing, protected mode is an operational mode that an 80286 or later Intel processor can operate in. Protected mode was developed with the 80286 CPU to allow multi-tasking programs to operate on a Persoanl Computer. When a processor is operating in protected mode, each running program is allocated an area of memory. Any program attempting to access memory outside its allocation generates an exception error which forces the offending program to be terminated without it overwriting memory in use by another program. Operating systems such as Unix, Windows 95, Windows 98, Windows NT, Windows 2000 and Windows XP all utilise protected mode.
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Protein is a long chain molecule made up of amino acids joined by peptide bonds.
Protein forms the structural material of bodily tissues.
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Protium is an isotope of hydrogen.
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A proton is a positively charged sub-atomic particle.
Proton was the name of a series of Soviet scientific satellites, the first launched in July 1965, designed primarily to study cosmic particles of super-high energies.
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A proxy cache is a computer cache system on a network, such as the Internet, often located near to a network gateway and used to reduce the bandwidth required over expensive dedicated internet connections. Proxy caches serve many users with cached files from many remote servers. Their primary usefullness is in caching files requested by one user for later retrieval by another. Some
proxy caches are part of cache hierarchies, in which a cache can ask neighboring caches for a requested file to reduce the need to fetch the file directly from it's source.
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Prussian blue (also formerly known as Berlin Blue) is a blue pigment discovered by Diesback (known as the Prussian) of Berlin in 1710. It is prepared by precipitating a ferric salt, such as ferrous sulphate, with a solution of potassium ferrocyanide. Prussian blue vaies from a slightly greenish blue to a blue tinged with violet and has a characteristic bronze lustre. Prussian blue has an intense colour and great staining strength but its noted for its transparency. Prussian blue is resistant to acid, but vulnerable to alkali.
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Psearch by Patri-Soft is an extension to the DOS computer operating system. You provide words or phrases, and it will scan directories to find files containing the text. Extensive file selection and pattern matching are provided. It provides an intelligent display of found text with a scroll back and program launcher. Psearch saves search results for later review. Psearch was recommended in PC World as one of the Best of Shareware products in 1990.
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Publisher's Paintbrush by ZSoft is a full-featured freehand-painting program that offers all the standard capabilities found in other painting programs (it is a superset of PC Paintbrush), plus some capabilities desktop publishers will find invaiuable. When creating or scanning a 300-dpi image, a 62 screen image is produced. Rather than editing the image screen-by-screen, you can zoom out and work on the multiscreen image in its entirety. The editing you do in normal mode can be handled in the zoomout mode.
The program lets you take full advantage of scanners, laser printers, and desktop publishing programs. Used with scanners, Publisher's Paintbrush gives you control over brightness and contrast, the resolution at which you want to scan the image, and the location on the page you want to scan. Publisher's Paintbrush lets you define the exact dimensions on the page of your scanned image which greatly reduces the amount of time it takes to scan and edit images.
Publisher's Paintbrush has very strong typography capabilities, making it ideal for creating illustrations that require sophisticated type. Type sizes are adjustable to any point size. You can slant the type to any angle to get curved type, italicise it as much or as little as you would like, and set the line and character spacing. Leading and keming are also adjustable. Publisher's Paintbrush lets you edit at the pixel level with 300 dpi full-page output.
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Puffer by Kent Briggs is a password-based data file and e-mail encryption utility for Microsoft Windows. It allows you to keep your personal, business, and electronic transmitted data private.
Puffer uses the highly rated Blowfish algorithm for fast, secure encryption and the Secure Hash Algorithm (SHA) for key generation. Three output formats are supported including binary, self- extracting executables, and 7-bit text for Internet e-mail.
Puffer also includes a three-pass, secure file wipe feature.
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Pugging is the process of mixing a pigment with a medium in such a way that the pigment forms a thick paste.
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Pulse Code Modulation (PCM) is the standard method of digitally encording audio. It is the basic uncompressed data format used to record audio CDs, and also by computer formats such as Windows .wav and Applie AIFF.
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Pulse modulation is a radio modulation method in which the timing, amplitude, and/or spacing of pulses of a transmitter's carrier are varied in order to convey information.
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A pump is a machine for moving fluid from one place to another.
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A punch is a machine for making or starting holes.
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Purilase are enzymes used to assist the breakdown of starch in effluent treatment plants.
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Purisol is a specialised macro-nutrient solution to enhance performance in biological effluent treatment plants.
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Purple is a secondary colour compounded by the union of the primaries blue and red. As a dye it was originally obtained from Tyrian dye.
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Purple of Cassius is a purple pigment generally obtained by precipitating a solution of gold choride by partially oxidized stannous chloride. It consists of oxides of tin, along with finely divided gold and is used for colouring enamels and artificial gems.
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In chemistry, a purpurate is a salt of purpuric acid.
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Pus is a yellowish liquid that forms in the body as a result of bacterial infection.
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Putty is a kind of paste or cement compounded of whiting or soft carbonate of lime and (usually) linseed oil, beaten or kneaded to the consistency of dough. It is used by glaziers for fitting window panes and also by house painters to stop up holes in wood-work prior to painting.
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Putty-powder is a pulverised oxide of tin sometimes mixed with oxide of lead. It is extensively used for polishing and other purposes in glass and marble works.
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The pyrheliometer is an instrument devised by Pouillet for measuring the intensity of the heat of the sun. It consists of a shallow cylindrical vessel of thin silver or copper, containing water or mercury in which a thermometer is plunged. The upper surface of the vessel is covered with lamp- black so as to make it absorb as much heat as possible, and the vessel is attached to a support in such a way that the upper surface can be always made to receive the rays of the sun perpendicularly.
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Pyridine is a basic compound occurring in coal tar and in the oil obtained by the distillation of bones. It is the parent substance of a large number of derivatives, including some of the natural alkaloids, such as nicotine and piperine. Pyridine is sometimes used for denaturing alcohol, so as to render it unfit to drink.
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Pyrocatechin is ortho-dihydroxy-benzene. It is formed when catechin and similar bodies are distilled, and is prepared from guaicol, occurring in beech tar by heating with hydriodic acid. Pyrocatechin forms white crystals that dissolve in water. Its solution is turned green by ferric chloride, and acts as reducing agent, particularly in alkaline solution. It has been employed as a photographic developer.
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Pyrogallic Acid (pyrogallol) is an acid obtained by the dry distillation of gallic acid. It forms colourless, odourless crystals, is readily soluble in water, alcohol and ether and its alkaline solution readily absorbs oxygen. It is used as a developer in photography.
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Pyroligneous Acid is an impure acetic acid obtained by the distillation of wood.
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A pyrometer is a device for measuring temperatures outside of the range of a mercurial thermometer.
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A pyroscope is an instrument for measuring the intensity of heat radiating from a hot body, or the frigorific influence of a cold body.
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Pyroxylic or wood spirit is the crude spirit obtained by distilling the volatile product of the dry distillation of wood, from which the tar has been separated and the acetic acid neutralized by lime. It consists chiefly of methyl alcohol and acetone, along with a number of other compounds, and is a brownish inflammable liquid. It is used as a solvent for making varnishes and also to mix with ordinary alcohol to denature it.
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Pyroxylin is an alternative name for notro-cellulose. The term pyroxylin is usually applied to the more soluble types of nitro-cellulose.
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Pyruvic acid (2-oxopropanoic acid) is a colourless liquid organic acid with the formula CH3COCOOH. It is an important intermediate compound in metabolism, being produced during glycolysis and converted to acetyl coenzyme A, required for the Krebs cycle.
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