06413_23 - X Y Z The element was discovered in 1898 by Ramsey and Travers xanthates Salts or esters containing the group SCS(OR where R is an

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X xanthates Salts or esters containing the group –SCS(OR), where R is an or- ganic group. Cellulose xanthate is an intermediate in the manufacture of * rayon by the viscose process. xanthophyll A member of a class of oxygen-containing * carotenoid pigments, which provide the characteristic yellow and brown colours of autumn leaves. X chromosome See sex chromosome . xenobiotic Any substance foreign to living systems. Xenobiotics include drugs, pesticides, and carcinogens. * Detoxi Ü ca- tion of such substances occurs mainly in the liver. xenolith A piece of pre-existing rock that occurs as an inclusion within an ig- neous * intrusion. Often it is a fragment of the country rock surrounding the in- clusion, although it may have been modi Ü ed to a hybrid rock by the intense heat of the intruding magma. xenon Symbol Xe. A colourless odour- less gas belonging to group 18 of the peri- odic table ( see noble gases ); a.n. 54; r.a.m. 131.30; d. 5.887 g dm –3 ; m.p. –111.9 ° C; b.p. –107.1 ° C. It is present in the atmos- phere (0.00087%) from which it is ex- tracted by distillation of liquid air. There are nine natural isotopes with mass num- bers 124, 126, 128–132, 134, and 136. Seven radioactive isotopes are also known. The element is used in Û uores- cent lamps and bubble chambers. Liquid xenon in a supercritical state at high tem- peratures is used as a solvent for infrared spectroscopy and for chemical reactions. The compound Xe + PtF 6 was the Ü rst noble-gas compound to be synthesized. Several other compounds of xenon are known, including XeF 2 , XeF 4 , XeSiF 6 , XeO 2 F 2 , and XeO 3 . Recently, compounds have been isolated that contain xenon– carbon bonds, such as [C 6 H 5 Xe][B(C 6 H 5 ) 3 F] (penta Û uorophenylxenon Û uoroborate), which is stable under normal conditions. The element was discovered in 1898 by Ramsey and Travers. xeric Denoting conditions characterized by an inadequate supply of water. Xeric conditions exist in arid habitats, ex- tremely cold habitats, and in salt marshes. Certain plants are adapted to live in such conditions. See halophyte ; xerophyte . xeromorphic Describing the structural modi Ü cations of certain plants ( * xero- phytes) that enable them to reduce water loss, particularly from their leaves and stems. xerophyte A plant that is adapted to live in conditions in which there is either a scarcity of water in the soil, or the at- mosphere is dry enough to provoke ex- cessive transpiration, or both. Xerophytes have special structural ( xeromorphic ) and functional modi Ü cations, including swol- len water-storing stems or leaves ( see suc- culent ) and specialized leaves that may be hairy, rolled, or reduced to spines or have a thick cuticle to lower the rate of transpiration. Examples of xerophytes are desert cacti and many species that grow on sand dunes and exposed moorlands. Some
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This note was uploaded on 05/29/2009 for the course CIVIL ENG 12345 taught by Professor Xhfxfh during the Spring '09 term at Amirkabir University of Technology.

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06413_23 - X Y Z The element was discovered in 1898 by Ramsey and Travers xanthates Salts or esters containing the group SCS(OR where R is an

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