| hydrate crystal | One of several possible microstructural arrangements of water molecules based on intermolecular forces; suggested as being involved in the mode of action of inhalation anaesthetics. (05 Mar 2000) |
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| hydrate microcrystal theory of anaesthesia | A theory of narcosis pertaining to nonhydrogen-bonding agents; postulates the interaction of the molecules of the anaesthetic drug with water molecules in the brain. Synonym: Pauling's theory. (05 Mar 2000) |
| hydrated | Combined with water, forming a hydrate. Synonym: hydrous. (05 Mar 2000) |
| hydrated alumina | <chemical> Hydrated aluminum. A compound with many biomedical applications: as a gastric antacid, an antiperspirant, in dentifrices, as an emulsifier, as an adjuvant in bacterins and vaccines, in water purification, etc. Pharmacological action: antacids, pharmaceutic aid. Chemical name: Aluminum hydroxide (Al(OH)3) (12 Dec 1998) |
| hydration | The condition of being combined with water. (18 Nov 1997) |
| hydraulic | Of or pertaining to hydraulics, or to fluids in motion; conveying, or acting by, water; as, an hydraulic clock, crane, or dock. Hydraulic accumulator, an accumulator for hydraulic machinery of any kind. See Accumulator. Hydraulic brake, a cataract. See Cataract. Hydraulic cement, a cement or mortar made of hydraulic lime, which will harden under water. Hydraulic elevator, a lift operated by the weight or pressure of water. Hydraulic jack. See Jack. Hydraulic lime, quicklime obtained from hydraulic limestone, and used for cementing under water, etc. Hydraulic limestone, a limestone which contains some clay, and which yields a quicklime that will set, or form a firm, strong mass, under water. Hydraulic main An inverted cup with a partition dipping into water, for opening or closing communication between two gas mains, the open ends of which protrude about the water. Origin: F. Hydraulique, L. Hydraulicus, fr. Gr, a water organ; "ydwr water + flute, pipe. See Hydra. Source: Websters Dictionary (01 Mar 1998) |
| hydraulic conductivity | Ease of pressure filtration of a liquid through a membrane; specifically, Kf = η(Q/A) (dx/dP), where Kf = hydraulic conductivity, η = viscosity of the liquid being filtered, Q/A = volume of liquid filtered per unit time and unit area, and dx/dP = reciprocal of the pressure gradient through the membrane; solute concentrations should be identical on both sides of the membrane. Also applied more loosely to measurements on a total membrane of unknown area and thickness with unmeasured fluid viscosity (K = Q/dP). (05 Mar 2000) |
| hydraulic load | Amount of liquid going into a system. (05 Dec 1998) |
| hydraulic motor | By altering the internal osmotic pressure within a cell, water will enter and a considerable expansion of the compartment will occur. This has been used as a motor device in plants (turgor pressure), in eversion of nematocysts and possibly in the production of other cellular protrusions. (18 Nov 1997) |
| hydraulics | That branch of science, or of engineering, which treats of fluids in motion, especially of water, its action in rivers and canals, the works and machinery for conducting or raising it, its use as a prime mover, and the like. As a science, hydraulics includes hydrodynamics, or the principles of mechanics applicable to the motion of water; as a branch of engineering, it consists in the practical application of the mechanics of fluids to the control and management of water with reference to the wants of man, including canals, waterworks, hydraulic machines, pumps, water wheels, etc. Some writers treat hydraulics and hydrostatics as subdivisions of hydrodynamics. Origin: Cf. F. Hydraulique. Source: Websters Dictionary (01 Mar 1998) |
| hydrazide | An organic compound of the general formula RCO-NHNH2; an acyl derivative of hydrazine. (05 Mar 2000) |
| hydrazine | <chemistry> Any one of a series of nitrogenous bases, resembling the amines and produced by the reduction of certain nitroso and diazo compounds; as, methyl hydrazine, phenyl hydrazine, etc. They are derivatives of hydrazine proper, H2N.NH2, which is a doubled amido group, recently (1887) isolated as a stable, colourless gas, with a peculiar, irritating odour. As a base it forms distinct salts. Synonym: diamide, amidogen, (or more properly diamidogen), etc. Origin: Hydr- + azo- + -ine. Source: Websters Dictionary (01 Mar 1998) |
| hydrazine yellow | <chemistry> An artificial dyestuff obtained as an orange-yellow powder, and regarded as a phenyl hydrazine derivative of tartaric and sulphonic acids. Origin: Tartaric + hydrazine. Source: Websters Dictionary (01 Mar 1998) |
| hydrazinolysis | Cleavage of chemical bonds by hydrazine (NH2-NH2); applied in protein and nucleic acid degradations. (05 Mar 2000) |
| hydrazone | A substance derived from aldehydes and ketones by reaction with hydrazine or a hydrazine derivative to give the grouping ==C==N-NH2. (05 Mar 2000) |