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NAT 



N 



NA'CRE. (nacre, Fr. ndcchera, It.) A 

 sort of mother-of-pearl. The fossil ink- 

 bags of belemnites found in the lias are 

 surrounded by nacre. 



NA'CREOUS. Glistening ; silvery ; irri- 

 descent. Having the appearance of mo- 

 ther-of-pearl. Many membranous shells 

 exhibit a necreous appearance on their 

 internal surface, as the Halioti?., or sea- 

 ear ; Anodon, or fresh-water muscle, &c. 



NA'CRITE. (from nacre.) A mineral so 

 called in consequence of its pearly lustre. 

 The Talcite of Kirwan. Nacrite occurs 

 in reniform masses, composed of extremely 

 minute spangles, or glittering scales. Co- 

 lour pearly grey, with a tinge of red or 

 green. It fuses easily before the blow- 

 pipe. When rubbed between the fingers 

 it leaves a pearly gloss. Unctuous to 

 the touch. Its constituents are, silex 

 56*0, alumine 18-25, potash 8-50, lime 

 3-10, iron 4-20, water 6-0. 



NA'KED. (nackt, Germ.) 



1. In botany, applied to flowers having no 

 calices ; to stems without leaves ; also to 

 leaves when perfectly smooth, and quite 

 destitute of hairs. 



2. In zoology, applied to molluscs, when 

 the body is not defended by a calcareous 

 shell. 



NA'NDIT. An ostrich of America ; the Rhea 

 Americana. 



NA'PHTHA. (vd<p9a, Gr. naptha, Lat. 

 naphte, Fr.) A variety of bitumen, 

 thin, volatile, fluid, and inflammable ; 

 unctuous to the touch, and constantly 

 emitting a strong odour. Colours yel- 

 lowish-white and yellowish-grey ; trans- 

 parent. Specific gravity from 0'70 to 

 0"85. It is highly combustible, igniting 

 even on the approach of a lighted taper. 

 It burns with a white or bluish flame, 

 yields a dense smoke, and yields no resi- 

 duum. It is insoluble in alcohol. When 

 long exposed to the air, it becomes yellow 

 and then brown ; its consistence is in- 

 creased, and it passes into petroleum. 

 Naphtha consists of carbon 82-2, hydro- 

 gen 14 '8. Springs of it exist in many 

 countries, particularly in the neighbour- 

 hood of volcanoes. The finest varieties 

 of naphtha are found on the shores of 

 the Caspian. The soil is sandy and 

 marly, and the surrounding minerals are 

 calcareous. The naphtha is constantly 

 rising in the state of an odorous inflam- 

 mable vapour. Naphtha is burnt in lamps 

 instead of oil. 



NA'RWAL. } (narkwal, narwall, Germ, the 



NA'RWHAL. $ sea unicorns.) The Mo- 



nodon monoceros of Linnaeus. Placed 

 by Cuvier in the family Cetacea ordi- 

 naria, order Cetacea. The tusk of this 

 animal is sometimes ten feet long, and 

 spirally furrowed. Portions of the skull 

 of the narwhal have been found in the 

 Lewes levels, in Sussex. 



NA'RES. (from naris, Lat.) The nos- 

 trils, 



NA'SAL. (from nasus, a nose, Lat. nasal, 

 Fr. nasale, It.) Pertaining to the nose. 



NA'SCENT. (nascens, Lat. from nascor, to 

 be born.) Beginning to exist ; growing. 



NA'TANT. (from nato, Lat. to swim.) Swim- 

 ming in the water ; floating on the sur- 

 face of the water. 



NA'TATORY. (from natator, Lat. a swim- 

 mer.) Enabling to swim. Certain or- 

 gans possessed by many animals are 

 natatory organs. Several of the cephal- 

 pods and pteropods, and other mollus- 

 cans, have natatory appendages. 



NA'TICA. A genus of nearly globose, um- 

 bilicated, univalves, belonging to the fa- 

 mily Neritacea. Aperture entire and 

 semicircular ; columella transverse, with- 

 out teeth, and callous externally. These 

 shells, though strongly resembling Ne- 

 ritse, may be distinguished from those of 

 that genus by their being always umbili- 

 cated, and the columella never dentated. 

 The recent Natica is found in estuaries and 

 tidal rivers, in mud and sandy mud, at 

 depths varying to forty fathoms. 



Several species of fossil Natica are 

 found in the London clay ; Bognor sand- 

 stone ; Gait ; and in the Shanklin sand. 



NA'TROLITE. The Natrolith of Werner; 

 Natrolithe of Haiiy. Considered by some 

 mineralogists to be a variety of prismatic 

 zeolite. Occurs in small, reniform, 

 rounded, or irregular masses, composed 

 of very minute fibres. The fibres are 

 divergent, or even radiate from a centre, 

 and are sometimes extremely minute and 

 close. Colours yellow, yellowish brown, 

 and brown, with striped-colour delinea- 

 tions* Translucent at the edges. Spe- 

 cific gravity 2-16 to 2'20. Before the 

 blow-pipe it fuses readily into a white 

 glass. In nitric acid it is reduced, with- 

 out any effervescence, into a thick jelly. 

 It derives its name from containing soda. 

 Its constituents are silex 48-20, alumine 

 24-50, soda 16-10, oxide of iron 1'75, wa- 

 ter 9-0. It occurs principally at Roegau, 

 in Suabia, imbedded in amygdaloid. 



NA'TRON. (natron, Fr.) The Soude car- 

 bonatee of Haiiy ; L' alkali mineral natif 

 of Brochant ; the Natron of Kirwan ,. A 



