Interesting

Why would graphite have been confused with lead?

Why would graphite have been confused with lead?


We are searching data for your request:

Forums and discussions:
Manuals and reference books:
Data from registers:
Wait the end of the search in all databases.
Upon completion, a link will appear to access the found materials.

I was reading the wikipedia page for pencil, and came across an interesting fact:

Prior to 1565 (some sources say as early as 1500), a large deposit of graphite was discovered on the approach to Grey Knotts from the hamlet of Seathwaite in Borrowdale parish, Cumbria, England. This particular deposit of graphite was extremely pure and solid, and it could easily be sawn into sticks. It remains the only large-scale deposit of graphite ever found in this solid form. Chemistry was in its infancy and the substance was thought to be a form of lead.

My question is, why was graphite thought to be a form of lead? The density of graphite is ~2.2g/cm^3, while lead is 11.34g/cm^3. They're both gray--but I have a hard time believing that color was the only reason people thought at the time that it was a form of lead. I'm sure I'm missing some context here that someone could elucidate.


Theses minerals were confused because they are quite similar in appearance, attributes and possible usage.

Graphite was previously called plumbago meaning the mineral Galena also called lead glance, which is a lead containing ore, not pure lead (plumbum). The density of pure lead glance (PbS) is only 7.60 g/cm3. They both look really similar and were indeed used for similar applications, for example namely in cosmetics. Kohl and mascara are charcoal - or mainly carbon - and just this galena respectively. Graphite was previously also quite often confused with molybdenite, (density: 10.28 g/cm3) a substance also capable of marking smooth surfaces.

Going by density alone is not very useful when classifying minerals, since densities vary, despite containing the most wanted metal. The numbers cited by you and me are for the pure compounds, usually not found as such in nature.

Galenit is also quite soft, clocking just 2-3 on the Mohs-scale, compared to 1-2 for graphite.

Galena:
and graphite:
molybdenite:

All of these materials can be used as a solid lubricant as well. Making them of strategic importance for military purposes. England banned the export of pencils to Napoleonic France, since the containing graphite is ideal as a lining for casting cannonballs. (Source: Scientific American: Carbon Wonderland (2088))

Like galena graphite was also used to glaze or line pottery vessels, making them more fire proof.

The three minerals historically named galena, molybdena and plumbago have several common features - they are all soft, dark materials with a metallic lustre. Before the advent of modern chemical methods, these three substances were often mistaken for one another. Because galena (lead(ii) sulfide) was known to be a useful lead ore, it was commonly believed that molybdena and plumbago also contained lead. However, molybdena (which we call molybdenite today) was actually molybdenum(iv) sulfide, and plumbago was what we now call graphite.
(Anders Lennartson: "Made by molybdenum", Nature Chemistry, Vol 6, August 2014, p746.)

Most important is of course the actual application as a writing or drawing tool. Everyone now knows how graphite in pencils works, but a similar effect is achieved in using a stilus plumbeum. These drawing tools are said to originate in ancient Egypt and are allegdly also described by Pliny. This variation of metal point is today most often called a silver point, despite lead being the main component in most cases.

This then closes the circle since modern pencils, containing graphite, are in English often called lead pencil and in German always called Bleistift. Young students often wise crack about licking the tip of a pencil, being unsure whether "it is or is not dangerous" because "lead is toxic", "actually it is not lead and does not contain any lead, so it's safe". At least modern German word usage (and Danish, Dutch, possibly more) and many citizens still confuse the minerals.


The wiki page on graphite contains a bit on it, ultimately this discovery came well before (200 years) graphite was considered something different than 'black lead' https://en.wikipedia.org/wiki/Graphite:

Historically, graphite was called black lead or plumbago.[7][29] Plumbago was commonly used in its massive mineral form. Both of these names arise from confusion with the similar-appearing lead ores, particularly galena. The Latin word for lead, plumbum, gave its name to the English term for this grey metallic-sheened mineral and even to the leadworts or plumbagos, plants with flowers that resemble this colour.

The term black lead usually refers to a powdered or processed graphite, matte black in color.

Abraham Gottlob Werner coined the name graphite ("writing stone") in 1789. He attempted to clear up the confusion between molybdena, plumbago and black lead after Carl Wilhelm Scheele in 1778 proved that there are at least three different minerals. Scheele's analysis showed that the chemical compounds molybdenum sulfide (molybdenite), lead(II) sulfide (galena) and graphite were three different soft black minerals.

It should be noted that it resembles lead ore, not lead… which would presumably weigh a bit less. Wonder if I have my old mineral test kit. Some properties one tests for in identifying a substance:

Hardness. Graphite and Lead are both 1.5 on Moh's hardness scale (https://en.wikipedia.org/wiki/Mohs_scale_of_mineral_hardness). This meant not only did it have the same coloring, it had the same softness to it.

Streak. Both graphite and lead leave a streak on a streak plate.

Magnetism : Both lead and Graphite also show very similar behavior in the presence of a magnet, not magnetic but interacting with a magnetic field.

Graphite actually has a few properties that are quite misleading, as it is simply a carbon arrangement yet still acts as a 'semimetal' and operates as a semi-conductor.

Until you get into more advanced forms of chemical testing, lead and graphite behave much the same.


Graphite

Our editors will review what you’ve submitted and determine whether to revise the article.

Graphite, also called plumbago or black lead, mineral consisting of carbon. Graphite has a layered structure that consists of rings of six carbon atoms arranged in widely spaced horizontal sheets. Graphite thus crystallizes in the hexagonal system, in contrast to the same element crystallizing in the octahedral or tetrahedral system as diamond. Such dimorphous pairs usually are rather similar in their physical properties, but not so in this case. Graphite is dark gray to black, opaque, and very soft (with a hardness of 1 1 /2 on the Mohs scale), while diamond may be colourless and transparent and is the hardest naturally occurring substance. Graphite has a greasy feel and leaves a black mark, thus the name from the Greek verb graphein, “to write.” For detailed physical properties of graphite, see native element (table).

Graphite is formed by the metamorphosis of sediments containing carbonaceous material, by the reaction of carbon compounds with hydrothermal solutions or magmatic fluids, or possibly by the crystallization of magmatic carbon. It occurs as isolated scales, large masses, or veins in older crystalline rocks, gneiss, schist, quartzite, and marble and also in granites, pegmatites, and carbonaceous clay slates. Small isometric crystals of graphitic carbon (possibly pseudomorphs after diamond) found in meteoritic iron are called cliftonite.

Graphite is used in pencils, lubricants, crucibles, foundry facings, polishes, arc lamps, batteries, brushes for electric motors, and cores of nuclear reactors. It is mined extensively in China, India, Brazil, North Korea, and Canada.

Graphite was first synthesized accidentally by Edward G. Acheson while he was performing high-temperature experiments on carborundum. He found that at about 4,150 °C (7,500 °F) the silicon in the carborundum vaporized, leaving the carbon behind in graphitic form. Acheson was granted a patent for graphite manufacture in 1896, and commercial production started in 1897. Since 1918 petroleum coke, small and imperfect graphite crystals surrounded by organic compounds, has been the major raw material in the production of 99 to 99.5 percent pure graphite.


Rubber Erasers

"India rubber," evidently intended for use as a pencil eraser, was advertised by William H. Maurice, a Philadelphia, PA, stationer, in 1847. Erasers were attached to the ends of pencils by 1853, when Charles Goodyear wrote: "Pencil-Heads. These are made of the artist's India rubber. they are set into metal sockets. or are formed into rings or heads which are intended to slip over the ends of a wooden pencil. " (Charles Goodyear, The Applications and Uses of Vulcanized Gum-Elastic, Vol. II, New Haven, 1853, p. 39) "Rubber erasers" and "Rubber pencil-tips" are listed among the purchases for members of the 1869 Illinois Constitutional Convention. (Debates & Proceedings of the Constitutional Convention of the State of Illinois, Sept. 13, 1869) "Rubber erasers" were advertised by Charles J. Cohen, a Philadelphia, PA, stationer, in 1878. It was reported in 1880 that "The new style of rubber eraser inserted in the head of the pencil has proven very popular." (The American Bookseller, Jan. 1880, p. 16) Both a "Stationers' Rubber" and a rubber "Crystal Eraser" were advertised by The American News Co., New York, NY, in 1883, and the same company advertised "Rubber pencil and ink erasers" in 1884. (Hagley Museum and Library)


Who Invented the Pencil and When?

Pencils were invented in 1795 by a French scientist named Nicolas-Jacques Conte. He used a mixture of graphite, clay and water baked in a kiln to create the "lead" of the pencil. He then housed this mixture in a wooden frame for writing.

Conte created several different kinds of pencils depending on their intended use. He made round pencils for artists who would be drawing for long periods of time and needed comfort. He made square or polygonal pencils for draftsmen or carpenters so that the pencils would not roll away.

Despite the fact that the center of a pencil has long been referred to as "lead," pencils were never made of lead. They have always been composed of graphite. The misnomer came about when graphite was first discovered in the 15th century and mistaken for a form of lead.


Contents

Conrad Gesner described a lead holder pencil in 1565, but the lead had to be manually adjusted to sharpen it. [2] The earliest extant example of a mechanical pencil was found aboard the wreckage of HMS Pandora, which sank in 1791. [3]

The first patent for a refillable pencil with lead-propelling mechanism was issued to Sampson Mordan and John Isaac Hawkins in Britain in 1822. After buying out Hawkins' patent rights, Mordan entered into a business partnership with Gabriel Riddle from 1823 to 1837. The earliest Mordan pencils are thus hallmarked SMGR. [4] [5] After 1837, Mordan ended his partnership with Riddle and continued to manufacture pencils as "S. Mordan & Co". His company continued to manufacture pencils and a wide range of silver objects until World War II, when the factory was bombed.

Between 1822 and 1874, more than 160 patents were registered pertaining to a variety of improvements to mechanical pencils. The first spring-loaded mechanical pencil was patented in 1877 and a twist-feed mechanism was developed in 1895. The 0.9 mm lead was introduced in 1938, and later it was followed by 0.3, 0.5 and 0.7 sizes. Eventually, 1.3 and 1.4 mm mechanisms were available, and 0.4 and 0.2 versions are now produced.

The mechanical pencil became successful in Japan with some improvements in 1915 by Tokuji Hayakawa, a metalworker who had just finished his apprenticeship. It was introduced as the "Ever-Ready Sharp Pencil". Success was not immediate since the metal shaft—essential for the pencil's long life—was unfamiliar to users. The Ever-Ready Sharp began selling in huge numbers after a company from Tokyo and Osaka made large orders. [6] [7] Later, Tokuji Hayakawa's company got its name from that pencil: Sharp. [6]

At nearly the same time in the US, Charles R. Keeran was developing a similar pencil that would be the precursor of most of today's pencils. Keeran's design was ratchet-based, whereas Hayakawa's was screw-based. These two development histories – Hayakawa and Keeran – are often mistakenly combined into one. [8] Keeran patented his lead pencil in 1915 [9] and soon afterwards arranged production. [8] After some improvements, his design was marketed as the "Eversharp" pencil by the Wahl Adding Machine Company by the early 1920s, Wahl had sold more than 12,000,000 Eversharps. [8]

Some of the manufacturers are: Pentel, Pilot, Tombow, Uni-ball and Zebra of Japan Faber-Castell, Lamy, Rotring and Staedtler of Germany Koh-i-Noor Hardtmuth of the Czech Republic Bic of France Monami of South Korea PaperMate and Parker of USA Caran d'Ache of Switzerland and numerous Chinese as well as other Asian and European manufacturers.

Mechanical pencils can be divided into two basic types: those that both hold the lead and can actively propel it forward, and those that only hold the lead in position.

Screw-based pencils advance the lead by twisting a screw, which moves a slider down the barrel of the pencil. This was the most common type in the earlier part of the twentieth century. Many of these have a locking mechanism one way to allow the lead to be pushed back into the pencil.

A clutch pencil (or leadholder) tends to use thicker leads (2.0–5.6 mm) and generally holds only one piece of lead at a time. A typical clutch pencil is activated by pressing the eraser cap on the top, to open the jaws inside the tip and allow the lead to freely drop through from the barrel (or back into it when retracting). Because the lead falls out freely when the jaws are opened, its forward movement cannot be controlled except by external means. This can be easily done by keeping the tip of the pencil a few millimeters above a work surface or the palm of one's hand. Some clutch pencils do have mechanisms which incrementally advance the lead, such as the Alvin Tech-Matic leadholder, but these are not normally considered to be in the same category as most pencils with propelling mechanisms.

Ratchet-based pencils are a variant of the clutch pencil, in which the lead is held in place by two or three small jaws inside a ring at the tip. The jaws are controlled by a button on the end or the side of the pencil. When the button is pushed, the jaws move forward and separate, allowing the lead to advance. When the button is released and the jaws retract, the "lead retainer" (a small rubber device inside the tip) keeps the lead in place, preventing the lead from either falling freely outward or riding back up into the barrel until the jaws recover their grip. Other designs use a precisely-fitted metal sleeve to guide and support the lead, and do not need a rubber retainer.

In one type of ratchet-based pencil, shaking the pencil back and forth causes a weight inside the pencil to operate a mechanism in the cap. A button may be present on the top or side of the pencil, to allow the user to advance the lead manually when necessary. Another variation advances the lead automatically. In this design, the lead is advanced by a ratchet but only prevented from going back into the pencil, just held from falling by a small amount of friction. The nib is a spring-loaded collar that, when depressed as the lead is worn away, extends out again when pressure is released.

An advanced ratchet type has a mechanism that rotates the pencil lead 9° counter-clockwise every time the lead is pressed on to the paper (which counts as one stroke), to distribute wear evenly. This auto-rotation mechanism keeps the lead 50% narrower than in the common propelling mechanical pencils, resulting in uniform thickness of the lines written onto the paper. The design was first patented by Schmidt of Germany, and later developed by Mitsubishi Pencil Company of Japan, and named Kuru Toga under the Uni brand. [10] This type of pencil is most suited for Asian languages that have multiple strokes per letter or word, where the pencil is frequently lifted off the paper. The mechanism is not suitable for cursive writing used in western scripts. Another recent auto-rotation movement by Uni rotates the lead 18 degrees per stroke (or 20 strokes per complete revolution), which is better suited for western scripts.

There exist protection mechanisms that prevent the lead from breaking (within certain limits) when excessive pressure is exerted while writing. A mechanism employed in the DelGuard system by Zebra of Japan causes the lead sleeve to extend outward when excessive pressure is applied at an angle. When excess vertical pressure is applied on the lead, the lead is automatically retracted inwards.

Higher-end mechanical pencils often feature a lead hardness grade indicator and sometimes feature a retractable lead guide pipe. This allows the lead guide pipe to retract back into the pencil body, which will keep it protected in storage and during transit and makes it 'pocket-safe'.

In spite of the name, pencil leads do not contain the toxic chemical element lead, but are typically made with graphite and clay, or plastic polymers. Compared to standard pencils, mechanical pencils have a smaller range of marking types, though numerous variations exist. Most mechanical pencils can be refilled, but some inexpensive models are meant to be disposable and are discarded when empty.

Diameter Edit

Mechanical pencil mechanisms use only a single lead diameter. Some pencils, such as the Pentel Function 357, place several mechanisms within the same housing, so as to offer a range of thicknesses (in this case three: 0.3, 0.5 and 0.7 mm). 1.00 mm leads also exist, but they are very rare. (See table below.).

Different sizes of lead diameters are available to accommodate various preferences and pencil builds, as shown in the table below. The more common lead sizes are 0.5 mm and 0.7 mm, whose line widths provide a favourable balance between precision and strength. Less common lead sizes can range from 0.2 mm up to 5.6 mm. Pentel has also previously demonstrated a prototype 0.1 mm pencil. [11] Pencils with sub-millimeter leads can usually hold multiple leads at the same time, reducing the frequency of refills. One exception was the Pentel 350 E, possibly Pentel's first mechanical pencil, [12] which could only hold a single stick of 0.5 mm lead. Refill leads can be bought in small tubes and inserted into the barrel as needed.

Diameter
(mm)
Diameter
(in)
Uses
0.20 (0.008) technical work
0.30 0.012 technical work (also known as 0.35 mm in certain German manufacturers)
0.40 (0.016) technical work (only available in Japan)
0.50 0.02 general writing, general technical work, beginner's technical work
0.60 (0.024) general writing (only available in Japan, discontinued by Tombow) [13]
0.70 0.028 general writing
0.80 (0.031) general writing
0.90 0.036 students/general writing (also known as 1.0 mm in certain German manufacturers)
1.00 0.040 rare, used in pre-1950 Parker pencils
1.18 3/64 or 0.046 older, used in pencils like the Yard-O-Led
1.30 (0.051) Staedtler and Pentel (colour leads only for Pentel)
1.40 (0.055) Faber-Castell e-Motion and the new Lamy ABC as well as some Stabilo children's pencils
2.00 0.075 or 0.078 drafting leadholders
3.15 1/8 (0.138) non-drafting leadholders
5.60 7/32 (0.220) non-drafting

The bracketed values in inches were found by calculation and rounded to 3 decimal places.

Hardness Edit

As with non-mechanical pencils, the leads of mechanical pencils are available in a range of hardness ratings, depending on the user's desired balance between darkness and durability. A commonly-used mechanical pencil lead is identical in density, but not in thickness to a traditional HB (US#2) pencil lead.

Pigments Edit

Mechanical pencils with colored leads are less common, but do exist. Crayola's "Twistable" product line includes two different types of colored pencils (erasable and non-erasable) with mechanical feed mechanisms, but does not offer refill leads. Several companies such as Pentel, Pilot, and Uni-ball (Mitsubishi Pencil Co.) currently manufacture colored refill leads in a limited range of diameters (0.5 mm, 0.7 mm, or 2.0 mm) for their own products. Koh-i-Noor makes mechanical colored pencils with replaceable leads in 2.0, 3.15 and 5.6 mm sizes. [14]


Since pencils do not use lead, there is very little to be concerned regarding lead exposure. The only relevant concern may be the yellow paint used to color the outside of them. In The United States, the Consumer Product Safety Commission regulates that the lead used in paint be no more than ninety parts per million, which is well below the amount used in the lacquer to color pencils.

Rosalie King began writing professionally in 2009. She is the author of "The Skin Underneath," a free ebook download, and is currently at work on "White Collar Ghetto." She studied clarinet in college, and has a Bachelor of Arts in music from the University of Tampa.


Why would graphite have been confused with lead? - History

Today I found out why lead used to be added to gasoline.

“Tetraethyl lead” was used in early model cars to help reduce engine knocking, boost octane ratings, and help with wear and tear on valve seats within the motor. Due to concerns over air pollution and health risks, this type of gas was slowly phased out starting in the late 1970’s and banned altogether in all on-road vehicles in the U.S. in 1995.

For a more detailed explanation of why lead used to be added to gasoline, it’s necessary to understand a little bit more about gasoline and what properties make it a good combustion material in car engines. Gasoline itself is a product of crude oil that is made of carbon atoms joined together into carbon chains. The different length of the chains creates different fuels. For example, methane has one carbon atom, propane has three, and octane has eight carbon atoms chained together. These chains have characteristics that behave differently under various circumstances characteristics like boiling point and ignition temperature, for instance, can vary greatly between them. As fuel is compressed in a motor’s cylinder, it heats up. Should the fuel reach its ignition temperature during compression, it will auto-ignite at the wrong time. This causes loss of power and damage to the engine. Fuels such as heptane (which has 7 carbon atoms chained together) can ignite under very little compression. Octane, however, tends to handle compression extremely well.

The higher the compression in the cylinders a car’s motor can produce, the greater the power it can get out of each stroke of the piston. This makes it necessary to have fuels that can handle higher compression without auto-igniting. The higher the octane rating, the more compression the fuel can handle. An octane rating of 87 means the fuel is a mixture of 87% octane and 13 percent heptane, or any mixture of fuels or additives that have the same performance of 87/13.

In 1919, Dayton Metal Products Co. merged with General Motors. They formed a research division that set out to solve two problems: the need for high compression engines and the insufficient supply of fuel that would run them. On December 9, 1921 chemists led by Charles F. Kettering and his assistants Thomas Midgley and T.A. Boyd added Tetraethyl lead to the fuel in a laboratory engine. The ever present knock, caused by auto-ignition of fuel being compressed past its ignition temperature, was completely silenced. Most all automobiles at the time were subject to this engine knock so the research team was overjoyed. Over time, other manufacturers found that by adding lead to fuel they could significantly improve the octane rating of the gas. This allowed them to produce much cheaper grades of fuel and still maintain the needed octane ratings that a car’s engine required.

Another benefit that became known over time was that Tetraethyl lead kept valve seats from becoming worn down prematurely. Exhaust valves, in early model cars, that were subject to engine knocking tended to get micro-welds that would get pulled apart on opening. This resulted in rough valve seats and premature failure. Lead helped fuel ignite only when appropriate on the power stroke, thus helping eliminate exhaust valve wear and tear.

The problems with Tetraethyl lead were known even before major oil companies began using it. In 1922, while plans for production of leaded gasoline were just getting underway, Thomas Midgley received a letter from Charles Klaus, a German scientist, stating of lead, “it’s a creeping and malicious poison” and warned that it had killed a fellow scientist. This didn’t seem to faze Midley, who himself came down with lead poisoning during the planning phase. While recovering in Miami, Midgley wrote to an oil industry engineer that public poisoning was “almost impossible, as no one will repeatedly get their hands covered in gasoline containing lead…” Other opposition to lead came from a lab director for the Public Health Service (A part of the US Department of Health and Human Services ) who wrote to the assistant surgeon general stating lead was a “serious menace to public health”.

Despite the warnings, production on leaded gasoline began in 1923. It didn’t take long for workers to begin succumbing to lead poisoning. At DuPont’s manufacturing plant in Deepwater New Jersey workers began to fall like dominoes. One worker died in the autumn of 1923. Three died in the summer of 1924 and four more in the winter of 1925. Despite this, public controversy didn’t begin until five workers died and forty-four were hospitalized in Oct. of 1924 at Standard Oils plant in Bayway NJ.

The Public Health Service held a conference in 1925 to address the problem of leaded gasoline. As you would expect, Kettering testified for the use of lead, stating that oil companies could produce alcohol fuels that had the benefits that were provided by lead, however the volumes needed to supply a growing fuel hungry society could not be met. Alice Hamilton of Harvard University countered proponents of leaded gasoline and testified that this type of fuel was dangerous to people and the environment. In the end, the Public Health Service allowed leaded gasoline to remain on the market.

In 1974, after environmental hazards began to become overwhelmingly apparent, the EPA (Environmental Protection Agency) announced a scheduled phase out of lead content in gasoline. One way manufacturers met these and other emission standards was to use catalytic converters. Catalytic converters use a chemical reaction to change pollutants, like carbon monoxide and other harmful hydrocarbons, to carbon dioxide, nitrogen and water. Tetraethyl lead would tend to clog up these converters making them inoperable. Thus, unleaded gasoline became the fuel of choice for any car with a catalytic converter.

The requirements by the EPA, emission control mechanisms on cars, and the advent of other octane boosting alternatives spelled the end for widespread leaded gasoline use. Manufacturers soon found that cars could no longer handle such a fuel public tolerance of the environmental and health hazards would not allow it and it became cost prohibitive to continue producing it. On January 1, 1996, the Clean Air Act completely banned the use of leaded fuel for any on road vehicle. Should you be found to possess leaded gasoline in your car you can be subject to a $10,000 fine.

This hasn’t completely gotten rid of leaded gasoline. You are still permitted to use it for off road vehicles, aircraft, racing cars, farm equipment, and marine engines, in the United States.

If you liked this article, you might also enjoy our new popular podcast, The BrainFood Show (iTunes, Spotify, Google Play Music, Feed), as well as:


Assessing a patient with delirium

The approach to the patient with delirium is a pragmatic one dictated by circumstance. One approach is discussed in the box at the end of this article. The examining doctor needs to take advantage of any opportunity that arises in order to complete a comprehensive assessment.

The agitated delirious patient is a medical emergency and should not be transferred to a psychiatric ward. The most urgent consideration is the safety of the patient and others.

Diagnosis of the cause

Once the diagnosis of delirium is established, the factor which precipitated it may be obvious. A careful history and examination is required and it may be important to interview relatives and friends, particularly if alcohol may be a cause. A list of all drugs that may have been taken or recently discontinued should be checked this may require information from their general practitioner.

All patients with delirium should have a simple battery of blood tests and other investigations (table 4). In particular cases, or if the routine tests are unrevealing, more detailed investigations which may require expert assistance are considered.

Approach to the confused elderly patient in hospital (after Inouye 3 )

The EEG can be of some diagnostic value in delirium. Generalised slowing and disorganisation are the usual abnormalities. These changes are seen whether or not the delirium is of the hypo- or hyperactive type. Fast activity may be found in those withdrawing from drugs. The EEG is also useful to exclude seizure activity. Imaging with computed tomography or magnetic resonance imaging scans may rarely show a focal and causative abnormality. Subdural collections may also be unexpectedly discovered in patients with no recollection of injury. Cerebrospinal fluid examination may be needed when central nervous system infection, or subarachnoid or malignant meningitis, are considered.

Treatment

The treatment of a patient with delirium can be divided into:

treatment of the cause or precipitating factors

general management of the patient with delirium including elimination of other precipitating factors that may exacerbate the delirium (table 5).

Principles of treatment for delirium

Attention should be given to ensuring adequate respiratory function and proper hydration. The patient should be looked after in a calm, well lit atmosphere. Any unnecessary contacts or investigations should be avoided. If possible any intravenous lines, monitoring devices or urinary catheters should be removed. Everything should be done to promote rest and sleep. Familiar people should if possible be involved in his care. Cues to aid orientation in time and place should be regularly given and reinforced. Any contributory medication should be stopped or at least reduced. High dose thiamine should be administered to anyone who might be poorly nourished or withdrawing from alcohol. If possible, physical restraint or sedative drugs should be avoided but if necessary, drugs such as haloperidol can be given.

There is some interest in developing strategies to identify patients at risk of delirium and intervene to reduce possible predisposing factors.5

Outcome and prognosis

Mortality figures vary depending on the patient population and time period covered, but most series show a significantly increased mortality in patients who develop delirium. They are also more likely to be discharged to a nursing home rather than to home, and any recovery may be slow. They are more likely to develop dementia.

Assessment of a patient with delirium

Try to remove as many people as possible from the room. Encourage the patient to rest on the bed or sit in a chair, and talk quietly or just listen for a while. A cup of tea can be a good idea. Avoid touching the patient and do not attempt examination until you have gained the patient's trust. Turn down very bright lights. Try to exclude extraneous noises. If possible get a member of the family or another familiar face to be with the patient. The patient may feel safer sitting in a chair than put to bed, and cot sides on the bed just seem to make the fall out of bed more hazardous.

Start with observation. The patient may respond to stimuli normally ignored, like a telephone in a hall. Observe his general appearance and behaviour, and the content of his speech. Examine the mental state. Most particularly, test for orientation, attention, and cognitive function. Do not argue with the patient about delusions or paranoid ideas, but do not agree with them either!

Perform a physical examination. Look for evidence of autonomic nervous system dysfunction, tachycardia, and dehydration. Try to discover signs of systemic illness, focal neurological abnormalities, meningism, raised intracranial pressure or head trauma. Multifocal twitching, shivering, “lint-picking” movements, and asterixis are some of the involuntary movements seen in delirium. A standard, comprehensive neurological examination may be difficult, but observation is the key. Eye movements and fields may be tested by observation as the patient looks around. He may be persuaded to “follow” an interesting target such as a torch. Give the patient simple objects to look at and handle and observe coordination. Allow the patient to move around if necessary.

Try to get some simple blood tests done this can be usually done with reassurance and patience. Occasionally judicious sedation is necessary for further investigations. Sending an agitated patient to be scanned is likely to make the confusion worse and may not result in worthwhile images. Anaesthetising the patient can be dangerous and will result in greater confusion when the patient wakes up, though this should not prevent sedation for clinically essential investigations.

A full explanation and reassurance to relatives and, after recovery, to the patient is helpful.


10 Things You Probably Did Not Know About Eraser Technology

Fact #1: Before rubber came along, people undid their mistakes using wadded-up bread.

It's true, as Arthur C. Clarke said, that the most advanced technologies are indistinguishable from magic. It's not true, however, that the world's most magical technologies are all related to computers. What could be more magic, after all, than the eraser—the little wad of rubber that undoes your mistakes and changes, mark by tiny little pencil mark, human history?

Erasers as we know them today are a relatively modern invention. But erasers as a general category are age-old. The ancient Greeks and Romans relied on palimpsests and smoothable wax tablets to ensure erasability. Those gave way, eventually, to White-Out and Photoshop's "magic eraser" tool and, of course, the ultimate undoer of deeds: the delete key. But erasers are far from obsolescence — just as writing itself is far from obsolescence. Below, 10 things to know about erasers.

1. The original erasers were bread. Moist bread.
Until the 1770s, humanity's preferred way of erasing errant graphite marks relied on bread that had been de-crusted, moistened and balled up. While these erasers were cheap and plentiful, they had a distinct disadvantage: They were, you know, made of bread. They were susceptible, like all bread, to mold and rot. Talk about a kneaded eraser.

2. The same guy who discovered oxygen helped to invent erasers.
In 1770, the natural philosopher and theologian Joseph Priestley—discoverer of oxygen and, with it, the carbonated liquid we now know as soda water—described "a substance excellently adapted to the purpose of wiping from paper the mark of black lead pencil." The substance was rubber.

3. Erasers were invented by accident.
Though Joseph Priestly may have discovered rubber's erasing properties, it's the British engineer Edward Nairne who is generally credited with developing and marketing the first rubber eraser in Europe. And Nairne claimed to have come upon his invention accidentally: He inadvertently picked up a piece of rubber instead of breadcrumbs, he said, thereby realizing rubber's erasing properties.

4. "Rubber" actually gets its name from erasers.
It was Priestley who is generally credited for naming rubber. The erasing "substance" he described in 1770—initially referred to as "India gum"—required, he remarked, rubbing action on the part of the user. Thus, yep, a "rubber." The name ended up generally applying to erasers' construction material rather than erasers themselves, especially after Charles Goodyear figured out how to vulcanize the stuff in the mid-1800s. In Britain, erasers themselves are still often called "rubbers." (Which may lead to some confusion, maybe.)

5. Erasers don't just work manually they work chemically.
Pencils work because, when they are put to paper, their graphite mingles with the fiber particles that comprise the paper. And erasers work, in turn, because the polymers that make them up are stickier than the particles of paper—so graphite particles end up getting stuck to the eraser instead. They're almost like sticky magnets.

Malaysian-manufactured Pink Pearl erasers (Wikimedia Commons).

6. Pencils with built-in erasers on the tops are a largely American phenomenon.
Most pencils sold in Europe are eraser-less. Read into that cultural difference what you will.

7. Many erasers contain volcanic ash.
Those ubiquitous pink erasers, in particular—the pencil-toppers and Pink Pearls of the world—make use of pulverized pumice to add abrasiveness. And pumice is, of course, volcanic ash.

8. The little erasers on pencil ends are known as "plugs."
Yep. And those small bands of metal that contain the plugs are called "ferrules."

9. Many of today's most high-tech erasers are made of vinyl.
While the pink erasers you find on pencils are made of synthetic rubber, an increasing number of erasers are made of vinyl. Vinyl's durability and flexibility give erasers made of it "minimal crumbling," and offer, overall, "first-class erasing performance." Plus, obviously, the sound quality is richer with vinyl.

10. There are such things as electric erasers.
Seriously. These erasers supposedly offer "a smooth erasure with a minimum of paper trauma."


Molybdenum

Molybdenum is an ancient metal and its ore, molybdenite, was initially confused and used as graphite and the common lead, galena (PbS). Evidence of use of molybdenum alloys have been found from 14 th century when it was used in Japan to make swords. In 1754, Bengt Qvist, proposed for the first time that molybdenite does not contain lead. Molybdenum was discovered by Carl Wilhelm Scheele in 1778 and later in 1781 it was isolated as impure form by Peter Jacob Hjelm. The name molybdenum has been derived from Neo-Latin molybdaenum and from Greek word molybdos that means lead. The name has been given as initially molybdenum ores were primarily confused with lead ores [1].

Molybdenum

Periodic Table ClassificationGroup 6
Period 5
State at 20CSolid
ColorGray metallic
Electron Configuration[Kr] 4d5 5s1
Electron Number42
Proton Number42
Electron Shell2, 8, 18, 13, 1
Density10.22 g.cm-3 at 20°C
Atomic number42
Atomic Mass95.94 g.mol -1
Electronegativity according to Pauling2.16

Occurrence

It does not occur in free or elemental form in nature mostly it is present in minerals and ores. Molybdenum is not a rare element. It is ranked as the 54 th most abundant element in the earth and 42 nd most abundant element in the universe. It is present in around 10 parts per billion on earth and traces of molybdenum have been found on the moon [2]. Molybdenum is widely present in many enzymes of bacterial plants’ and animal’s origin and around 50 such enzymes have been reported. The most common minerals of molybdenum include molybdenite (MoS2), powellite and wulfenite. Molybdenum is produced commercially as a by-product of tungsten and copper mining. The largest producers of molybdenum are China, Peru, USA, Mexico and Chilli.

Physical Characteristics

Molybdenum is a greyish silver transition metal. It has significantly high melting point, around 2623 degree centigrade. Molybdenum has considerable low coefficient of thermal expansion as compared to other metals. It is a dense metal and has a density of around 10.28 g/cm 3 . Molybdenum has high tensile strength which increases significantly with a decrease in diameter. It does not readily dissolve in water in elemental form but most minerals of molybdenum are quite soluble in water.

Chemical Characteristics

Molybdenum is not a very reactive metal. Molybdenum occurs in a wide range of oxidation states, from -2 to +6 with having prevalence of higher oxidation states in various organic and inorganic compounds. The most stable oxidation states are +4 and +6. Molybdenum reacts with chlorine in wide range of oxidation states to form molybdenum (II, III, IV, and V) chloride. It does not react with water or oxygen at room temperature and at higher temperatures, 300 degree centigrade, molybdenum undergoes weak oxidation and at temperatures above 600 degree centigrade it undergoes significant oxidation to produce molybdenum trioxide. Molybdenum trioxide and molybdenum dioxide are the most commercially significant compounds of molybdenum

Significance and Uses

  • Molybdenum is used as fertilizers for certain plants for example cauliflower.
  • Molybdenum is also used to make steel alloys to impart weldability and resistance to corrosion.
  • Molybdenum disulphide is used as lubricant as it can withstand high temperature and pressure.
  • Molybdenum disilicide is used to make ceramic that has electrical conductivity.
  • Molybdenum trioxide is used to make adhesives to bind metals to enamels.
  • Molybdenum anodes are used in x-ray sources.

Health Effects

Molybdenum is biologically important element and is considered essential for life of most plants and animals. In bacteria molybdenum containing enzymes play important role in biological nitrogen fixation. Molybdenum is required in trace amount in human body and is part of four crucial mammalian enzymes [3]. The primary dietary sources of molybdenum include sunflower seeds, cucumber, lentils, green beans and eggs. Prolonged and high amount ingestion of molybdenum can lead to growth retardation, diarrhoea, low birth rate and damage to lungs and kidneys.

Isotopes of Molybdenum

There are around thirty five isotopes of molybdenum, with atomic mass ranging from 83 to 117. It only has 7 naturally occurring isotopes: molybdenum-92, molybdenum-94, molybdenum-95, molybdenum-96, molybdenum-97, molybdenum-98 and molybdenum-100.

Molybdenum-100 is the only naturally occurring unstable isotopes. It has a half-life of 10 19 years and undergoes decay through emission of beta particles and transform into ruthenium-100. The most stable, abundant and naturally occurring isotope is Molybdenum-98.

REFERENCES

[1]. Lide, David R., ed. (1994). “Molybdenum”. CRC Handbook of Chemistry and Physics. 4. Chemical Rubber Publishing Company. p. 18. ISBN 0-8493-0474-1.

[2]. Jambor, J.L. et al. (2002). “New mineral names” (PDF). American Mineralogist. 87: 181.

[3]. Schwarz, Guenter Belaidi, Abdel A. (2013). “Chapter 13. Molybdenum in Human Health and Disease”. In Astrid Sigel Helmut Sigel Roland K. O. Sigel. Interrelations between Essential Metal Ions and Human Diseases. Metal Ions in Life Sciences. 13. Springer. pp. 415–450. doi:10.1007/978-94-007-7500-8_13

Other Periodic Table Elements

Lead has been known since old ages and its use has been largely limited due&hellip

Tennessine is a synthetic element that was discovered in 2010. It is highly radioactive and&hellip

Moscovium is a synthetic element that was discovered in 2003. It is a highly radioactive&hellip

This site uses cookies to improve your experience. To find out more, see our cookie policy.


Flint, Michigan: Drinking water crisis

One of the most notorious cases of lead leaching into drinking water occurred recently in Flint, Michigan. In an effort to save money, officials had decided to switch the source of the city's drinking water from the Detroit Water and Sewerage Department (DWSD) to the Karegnondi Water Authority (KWA). In the meantime, however, they would need to pull water from the Flint River, beginning on April 25, 2014.

Within weeks, Flint residents began to complain about the smell and color of their tap water. Tests revealed high levels of E.coli and total coliform bacteria in the water supply, which prompted the city to chlorinate the water at higher-than-usual levels. This chlorination, in addition to the fact that they had not implemented any corrosion protection, caused massive pipe corrosion, allowing lead to leach into the drinking water.

In many homes, the levels of lead in the drinking water were far above the Environmental Protection Agency's maximum safety level of 15 parts per billion (ppb). In fact, the water in one home was tested by Virginia Tech researchers as having lead levels at 13,200 ppb — over three times the level considered to be hazardous waste. Unfortunately, a child living in that home was diagnosed with lead poisoning.



Comments:

  1. Aza

    I think you are wrong. I can prove it. Email me at PM.

  2. Gaarwine

    Cool words

  3. Nik

    No bad topic



Write a message