Pencil, pencils

Griffel, m. style, stylus slate pencil, pencil (Bot.) style. 

Use waterproof ink Never pencil Pencil will disappear with time, and so will your grade. Cheap ink will wash away and carry your grades down the drain. Never erase Just draw one line through yuor orrcro your errors so that they can still be seen. And never, never, never cut any pages out of the notebook ... 

The divergence factor (DF) introduced by the asymptotic expansion, accounts for the deformation of the refracted wavefront (initially spherical in the coupling medium). It ensures, under the GO approximation, the energy conservation of a ray-pencil propagating... 

Unlike most words in a glossary of tenns associated with the theoretical description of molecules, the word synnnetry has a meaning in every-day life. Many objects look exactly like their mirror image, and we say that they are syimnetrical or, more precisely, that they have reflection synnnetry. In addition to having reflection synnnetry, a pencil (for example) is such that if we rotate it tln-ough any angle about its long axis it... 

Method. Draw a light pencil line across the paper strip about 3 cm. from the bottom (Fig. 25 (b) ), and mark two points A and B 2 cm. 

The position of the spots should be marked in pencil, for the colours fade after some time. 

Method. Prepare a paper strip from Whatman No i filter paper, as in the previous experiment, and draw a light pencil line about 3 cm. from the bottom cf. Fig. 25(B)). Mark three points A, B and C symmetrically on this line, if possible 2 cm. apart. Using the fine pipette, or a capillary tube, apply sufficient of solution (A) to the point A to give a damp spot about 0-5 cm. in diameter. Using a thoroughly washed pipette or a fresh capillary tube on each occasion, apply solution (B) and (C) to the points B and C respectively. Dry the strip in the air. 

Inspect the paper in ultraviolet light—conveniently in front on a Hanovia ultraviolet strip light—in a dark room. The acids show up as intense blue fluorescent spots. Mark with a pencil the positions of all spots. The position of the two spots arising from solution (C) should be compared with the single spots arising from solutions (A) and (B). It is probable that the solution (B) of pure N-methylan-thranilic acid may also reveal a faint spot corresponding to anthranilic acid still present in minute traces in the methylated acid cf. p. 223). 

The mixture to be separated is dissolved in a suitable solvent and spotted on to a pencilled line at the bottom of the t.l.c. plate, ca. i o-i 5 cm. from the end. A suitable dropping tube may he made by drawing out the middle of a m.p. tube with a micro-burner and breaking the tube in the middle. The dropper is filled by capillary action and is discharged when the liquid at the tip drops on to the untouched absorbent surface the spot should be 2 5 mm. in diameter. 

Most chemists want to avoid the paper-and-pencil type of work that theoretical chemistry in its truest form entails. However, keep in mind that it is precisely for this kind of painstaking and exacting research that many Nobel prizes have been awarded. This book will focus almost exclusively on the knowledge needed to effectively use existing computer software for molecular modeling. 

The system of atomic units was developed to simplify mathematical equations by setting many fundamental constants equal to 1. This is a means for theorists to save on pencil lead and thus possible errors. It also reduces the amount of computer time necessary to perform chemical computations, which can be considerable. The third advantage is that any changes in the measured values of physical constants do not affect the theoretical results. Some theorists work entirely in atomic units, but many researchers convert the theoretical results into more familiar unit systems. Table 2.1 gives some conversion factors for atomic units. 

Statistical mechanics is the mathematical means to calculate the thermodynamic properties of bulk materials from a molecular description of the materials. Much of statistical mechanics is still at the paper-and-pencil stage of theory. Since quantum mechanicians cannot exactly solve the Schrodinger equation yet, statistical mechanicians do not really have even a starting point for a truly rigorous treatment. In spite of this limitation, some very useful results for bulk materials can be obtained. 

Some 500 years ago during Columbuss second voyage to what are now the Americas he and his crew saw children playing with balls made from the latex of trees that grew there Later Joseph Priest ley called this material rubber to describe its ability to erase pencil marks by rubbing and in 1823 Charles Macintosh demonstrated how rubber could be used to make waterproof coats and shoes Shortly there after Michael Faraday determined an empirical for mula of CsHs for rubber It was eventually determined that rubber is a polymer of 2 methyl 1 3 butadiene... 

Selig, W. S. Potentiometric Titrations Using Pencil and Graphite Sensors, /. Chem. Educ. 1984, 61, 80-81. 

Potassium alum, which also occurs naturally as the mineral kalinite [7784-24-9], KAl(SO 2 12H20, sp gr 1.75, is used ia tanning skins, as a mordant ia dyeiag, and ia the pharmaceutical and cosmetic iadustries (see Pharmaceuticals Cosmetics). It is used as a styptic pencil and as a hardening agent and set accelerator for cement and plaster. The ACGIH threshold limit value TWA is 2 mgAl/m (1 ). 

In many parts of the world, eg, China and northern Canada, block talc is used by the native artisans as a carving material and some of the sculptures produced ate widely treasured. Block talc is also used for manufacture of fireplaces in Finland and Vermont. Machined talc pencils have been used for marking steel during processing since the 1890s. 

Pitch. Pitch used to be stored in solid form at the tar distillery in open bays, from which it was removed by small explosive charges. Loading of the lump pitch by mechanical shovel created a dust ha2ard both at the tar installation and at the customer s, where the lumps had to be ground before use. In the 1990s, pitch is stored in tanks heated by superheated steam or circulating hot-oil coils and transported in fiquid form in insulated rad, road tankers, or ships. When transport as a hot fiquid is not feasible, not acceptable by the customer, or for small amounts, the pitch is converted into a dust-free particulate form, ie, short rods termed pencils, pastilles, or flakes. 

The risk of skin cancer by contact with pitch dust has in more recent years been reduced by the transport and handling of pitch as a Hquid or as dust-free flakes or pencils. Nevertheless, in handling coal-tar products, certain precautions should be taken. These have become obligatory in tar distilleries and plants using pitch or creosote. 

Erictional errors result from failure of the Hquid to perfectly wet the small thermometer bore. They can usually be removed by lightly tapping the thermometer stem, for example with a wooden pencil, before reading. 

Cellulose. Cellulose or starch xanthate cross-linked by titanates can adsorb uranium from seawater (536). CarboxymethylceUulose cross-linked with TYZOR ISTT is the bonding agent for clay, talc, wax, and pigments to make colored pencil leads of unusual strength (537). 

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