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Home >> Chemistry Dictionary >>Gabriel's Reaction - Gas Calorimeter
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Ga.
Gallium.
Gabriel’s reaction.
The conversion of a halogen compound into the corresponding amino compound by treatment with potassium phthalimide and subsequent hydrolysis of the intermediate phthalimide compound. Thus chloroethanoic acid gives glycine. The method is of general application and has the great advantage of giving a pure primary amine free from mixture with secondary and tertiary products.
Gadolinium.
Gd. A soft silvery metallic element. At.no.64, at.wt. 157.5, m.p. 13110C, b.p. 32330C, d 7.89.A lanthanide. The metal is hep (to 12620C) and bcc (to m.p.). The largest use of Gd is in ferrites and as the selenide for electronic equipment. Gd compounds are extensively used as catalysts, particularly olefine polymerization catalysts.
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Galactans.
Polysaccharides which on hydrolysis give galactose. They occur in wood and in many algae. The most important galactant is agar.
Galactose.
A simple sugar, C6H12O6, stereoisomeric with glucose, that occurs naturally as one of the products of the enzymic digestion of milk sugar (lactose) and as a constituent of gum arabic.
Galena.
PbS. A common lead ore, black or bluish-grey with a metallic lustre. It has the NaCl structure.
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Gallic acid.
3,4,5-trihydroxybenzoic acid, C7H6O5. A Colourless crystals with one molecule of water, m.p. 2530 C, sparingly soluble in water and alcohol. It is found free in woody tissue, gall-nuts and in tea, and is a constituent of the tannins, from which it can be obtained by fermentation or by acid hydrolysis. On heating it, gives pyrogallol. Gallic acid has a limited use as a dyestuffs intermediate and a s a source of medicinals and is used in the manufacture of ink.
Garnets.
A group of silicates, M3II M2III(SiO4)3 (MII = Ca, Mg, Fe; MIII=Al, Cr, Fe), containing discrete SiO44- groups. Some garnets are used as gemstones with colours ranging from yellow –red to deep –red and also emerald green. Garnet sand is used as an abrasive.
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Gallium.
Ga.At.no. 31, at.wt.69.72, m.p. 29.780C, b.p. 24030C, d 5.907. A silver white metal. Found in traces in Zn and Al minerals and in germanite (0.7% Ga.). The element, metallic in appearance, has a complex structure; it is obtained by electrolysis of Ga salts. It dissolves in acids (and alkalis) and becomes coated with a thin coating of oxide on heating in air.
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Galvanizing.
A process of covering steel with Zn for protection by dipping into molten Zn or by electrodeposition (cold galvanizing). Corrosion occurs preferentially at the Zn.
Gamma emission.
After a nuclear process, such as alpha or beta emission, has occurred, the resulting nucleus may get excited. The excess energy is released as gamma radiation and the nucleus returns to its ground state.
Gamma rays
(g-rays). Electromagnetic radiation of very short wavelength, that is very hard X-ray. g - Rays have great penetrating power and are emitted in most nuclear disintegrations.
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Gangue.
The clay and other silicate material associated with ores.
Gas.
The state of matter in which molecules have almost unrestricted motion. A substance for which the volume increase continuously and without limit as the pressure is continuously reduced. A vapour is distinguished from a gas in that a gas is above the critical temperature of the substance.
Gas absorption.
The solution of one component of a gaseous mixture in a liquid or the absorption on to a surface. Selective absorption is employed to separate components of mixtures of gases or vapours, e.g., the removal of NH3 from NH3 air mixtures by absorption in water.
Gas calorimeter.
Equipment for the determination of the calorific value of a fuel gas by burning at a known rate or for small amounts of combustible gas combustion or explosion of a known volume of gas.
Gas constant.
By combining Boyle’s and Charles’s laws, we arrive at a general equation of the form pv = kT, where p is the pressure , v the volume and T the temperature of the gas, while k is a constant depending on the amount of gas used, and the units employed for expressing p and v. When 1 mole of gas is considered, k may be replaced by R, and the equation becomes pv=RT. R is called the gas constant.R=0.8204 litre-atmos, per degree, or 8.31432/(mol)4 x 107 ergs per degree, or 1.987 cal per mole per degree.
Gas laws.
Laws which are relating the temperature, pressure, and volume of an ideal gas.
Gas mental.
A structure composed of the oxides of thorium (99%) and corim (1%) made by impregnating a combustible fabric with a solution of the nitrates of the metals and decomposing the nitrates by heat.
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