Pencil leads

Lead pencils first manufactured commercially during Queen Elizabeth s reign, using Cumberland graphite. 

Blei-feder, /. lead pencil, -flasche, /. lead bottle, -folie, /. lead foil, blei-frei, a. free from lead. -fUhrend, a. leadbearing, plumbiferous. 

Blei-grube, /. lead mine, -gumml, m. lead-pencil eraser (Min.) plumboresinite. bleihsltig, a. containing lead, plumbiferous, Blei-homerz, n. -hornspat, m. phosgenite. 

Graphite is planar, with the carbon atoms arranged in a hexagonal pattern. Each carbon atom is bonded to three others, two by single bonds, one by a double bond. The hybridization is sp2. The forces between adjacent layers in graphite are of the dispersion type and are quite weak. A lead pencil really contains a graphite rod, thin layers of which rub off onto the paper as you write (Figure 9.13, p. 242). 

Although hardness is a somewhat nebulous term, it can be defined in terms of the tensile modulus of elasticity. From a more practical side, it is usually characterized by a combination of three measurable parameters (1) scratch resistance (2) abrasion or mar resistance and (3) indentation under load. To measure scratch resistance or hardness, an approach is where a specimen is moved laterally under a loaded diamond point. The hardness value is expressed as the load divided by the width of the scratch. In other tests, especially in the paint industry, the surface is scratched with lead pencils of different hardnesses. The hardness of the surface is defined by the pencil hardness that first causes a visible scratch. Other tests include a sand-blast spray evaluation. 

The name mbber derives from the fact, noted in 1770 by Joseph Priestley the English chemist, that caoutchouc would erase or mb out lead pencil marks. Priestley did not actually name it mbber, but at some time between 1770 and 1778 the term became popular. 

Use a soft lead pencil to label nitrocellulose filters with a hash maik and letter or number on one edge to allow subsequent identification and orientation (see Note 1)... 

It is alleged that English scientist Joseph Priestly observed that the material could be used for rubbing out lead pencil marks and thus gave the material the name rubber. ( Introduction Lo the Theory of Perspective, Joseph Priestly, 1835.)... 

After the transfer period, turn off the power supply and disconnect the leads. Remove the cathode and uppermost three layers of filter paper. Cut the comer of the transfer membrane above the cut corner of the gel. Alternatively, mark the transfer membrane by tracing the gel with a soft lead pencil. 

Ordinary "lead" pencils actually are made of a form of carbon called graphite. If a pencil line is 0.35 mm wide and the diameter of a carbon atom is 1.5 X 1CT 10 m, how many atoms wide is the line ... 

The "lead" in lead pencils is actually almost pure carbon, and the mass of a period mark made by a lead pencil is about 0.0001 g. How many carbon atoms are in the period ... 

A black lead pencil should be used for the third drawing, which will be cubist ... 

A simpler method is to inscribe the surface using lead pencils in a range of hardness from 2H to 8H, and, if an impression is obtained, to note the type of pencil used. 

After examination, an area is chosen which is as far away from both the embryo and blood vessels as possible. This will be the site of inoculation so it is important not inject into a blood vessel as this will result in the death of the embryo. Using a soft-lead pencil this location is marked on the surface of the egg. 

Obtain an 8.5 in. by 8.5 in. piece of 3 MM Whatman filter paper from the instructor and draw a straight line across the bottom using a soft lead pencil about 1.5 in. from the edge of the paper. This line will designate the origin where your samples will be spotted. 

Spot 3 pi of each of the amino acid standards along the origin. As with the thin-layer chromatography plate, spot each sample 1 /u.1 at a time. Indicate the identity of each sample spot below the origin using a soft lead pencil. 

Obtain a strip of Whatman 3 MM chromatography paper (1 in. by 22 in). Draw a line with a soft lead pencil about 7 cm from one end of the strip. This line will mark the origin where the sample will be spotted. Keep in mind that the... 

Using a soft lead pencil, label the strip at the end opposite the origin with your name. 

F. Lead pencils will not be allowed in the clean room. Ball point pens only. 

The easy transfer to surfaces is probably the reason for the early names "plumbago" and "molybdaena", meaning lead-like, since lead also produces dark marks on paper and fabric. Lead rods were used in ancient times for marking out parchments, and this has led to the expressions "lead pencil" and "black-lead" which have been common until the twentieth century. Both terms now commonly refer to graphite, which resembles molybdenum disulphide in many ways, but the latter was almost certainly used in the same way until the late eighteenth century. The two materials can be easily distinguished by the lower density of graphite. 

The phenomenon in Exp. 57 (d) is due to what general chemical change Will chlorine bleach a lead pencil mark or newspaper ink Why Predict the result when red hot charcoal is thrust into a bottle of chlorine. 

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