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Home >> Chemistry Dictionary >> Grahams Law of Diffusion - Gutta Percha
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Gooch crucible. A porcelain dish having perforated base over which a layer of asbestos is kept. It is used for filteration in gravimetric analysis.
Gouy balance. A balance for the determination of magnetic susceptibility. The sample is weighed in and out of a magnetic field and the susceptibility is calculated from the difference in weights.
Graham’s law of diffusion. This law states that rates at which two gases diffuse are inversely proportional to their densities, i.e.
Rate A/rate B = √rB/rA
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Gram atom. The quantity of an element numerically equal to the atomic weight expressed in grams.
Gram equivalent. The equivalent weight of a substance expressed in grams.
Gram molecule. The quantity of a compound, or element, equal numerically to the molecular weight expressed in grams. The weight in grams of one mole of a substance
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Granite. An igneous rock extensively used as a building stone and road metal.
Graphite, plumbago, black lead. A form of carbon occurring and formed in crystalline and microcrystalline forms. The structure has parallel hexagonal sheets of carbon atoms. The C-C distance within the sheets is 1.42A, the distance found in aromatic rings. The C-C distance between is 3.40A and there is high conductivity along sheets, easy cleavage and ready incorporation or other substances between the layers (graphite compounds, lamellar compounds, intercalation compounds). Used as a lubricant, refractory, pencils, etc., electrical components, paints carbonizing steels.
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Gravimetric Analysis. Methods of analysis involving precipitation, etc. which end up with a final weighting of a stable derivative.
Graviton. An elementary particle: the particle which in wave form is a gravitational field.
Gray. Symbol. Gy. The derived SI unit of absorbed does of ionizing radiation.
Greases. A semi-solid lubricant composed of emulsified petroleum oils and soluble hydrocarbon so groups
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Green acids. The name given to Sulphonic acids which are present in the acid sludge phase following treatment of lubricating oil fractions with oleum or sulphuric acid. The Sulphonic acids in the oil phase are termed ‘mahogany acids’ used as emulsifiers, rust – proofing agents and lubricant additives. The water soluble green acids are not used.
Ground state. The lowest energy electronic, vibrational, or rotational state of an atom, molecule or ion.
Group. A vertical group of elements in the normal form of the periodic table. Within a group there are distinct chemical resemblances and gradations in properties.
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GSC. (Gas – solid chromatography) see gas chromatography.
Guanidine. A crystalline basic compound HN:C(NH2)2, related to urea.
Guanine. A purine derivative. It is one of the major component bases of nucleotides and the nucleic acids DNA and RNA.
Guest molecule. Refers to the molecules trapped inside the crystal host structure to form clathrates.
Gum. Any of a variety of substances obtained from plants. Typically they are insoluble in organic solvents but form gelatinous or sticky solutions with water. Gum resins are mixtures of gums and natural resins. Gums are produced by the young xylem vessels of some plants (mainly trees) in response to wounding or pruning. The exudate hardens when it reaches the plant surface and thus provides a temporary protective seal while the cells below divide to form a permanent repair. Excessive gum formation is a symptom of some plant diseases. See also mucilage.
Guncotton. Collulose nitrate, nitrocellulose. A powerful explosive formed by the action of nitric acid on cellulose.
Gun metal. A type of bronze usually containing 88 – 90% copper, 8 – 10% tin, and 2 – 4% zinc. Formerly used for cannons, it is still used for bearings and other parts that require high resistance to wear and corrosion.
Gunpowder. An explosive consisting of a mixture of potassium nitrate, sulphur, and charcoal.
Gutta percha. A naturally occurring polymeric material, isomeric with rubber but having the terms configuration. Now chiefly used as a rubber additive. Obtained from the latex of various tropical trees.
Gypsum. A monoclinic mineral form of hydrated calcium sulphate, CaSO4 2H2O. It occurs in five varieties: rock gypsum, which is often red stained and granular , gypsite, an impure earthy form occurring as a surface deposit; alabaster a pure fine grained translucent form; satin spar, which is fibrous and silky; and selenite, which occurs as transparent crystals in muds and clays. It is used in the building industry and in the manufacture of cement, rubber, paper, and plaster of Paris.
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