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NAPHTHALENE, C,oH8, a hydrocarbon discovered in the " carbolic " and " heavy oil " fractions of the coal-tar distillate (see COAL-TAR) in 1819 by A. Garden. It is a product of the action of heat on many organic compounds, being formed when the vapours of ether, camphor, acetic acid, ethylene, acetylene,, &c., are passed through a red-hot tube (M. Berthelot, Jahresb., 1851), or when petroleum is led through a red-hot tube packed with charcoal (A. Letny, Ber., 1878, II, p. 1210). It may be synthesized by passing the vapour of phenyl butylene bromide over heated soda lime (B. Aronheim, Ann., 1874, 171, p. 219); and by the action of ortho-xylylene bromide on sodium ethane tetracarboxylic ester, the resulting tetra-hydronaphthalene tetracarboxylic ester being hydrolysed and heated, when it yields hydronaphthalene dicarboxylic acid, the silver salt of which decomposes on distillation into naphthalene and other products (A. v. Baeyer and W. H. Perkin, junr., Ber., 1884, 17, P. 451):
C6H4<CH2Br+Na•C(CO2R)2	C6Ha ~•CHCH2•C2•C(CO(CO22RH)2
)2
CioH8	C6H9`CHCH22•CH H•C0CO22HH C6H4`CH2•C(CO2H)2
" Nape," the back of the neck, is of doubtful origin; it may be a variant of " knap," a knob or protuberance.
It is a colourless solid, which melts at 8o° C., and boils at 218° C. It crystallizes in the monoclinic system; it is to be noted that a- and /3-naphthol assume almost identical forms, so that these three compounds have been called isomorphous. It is insoluble in water, but is readily soluble in alcohol, and ether. It has a characteristic smell, and is very volatile, distilling readily in a current of steam. It acts as a weak antiseptic. It is used for enriching coal gas, as a vermin killer, in the manufacture of certain azo dyes, and in the preparation of phthalic acid (q.v.). When passed through a red-hot tube packed with carbon it yields f3/3-dinaphthyl, (C10H7)2. It forms a crystalline compound with picric acid. It readily forms addition products with chlorine and with hydrogen; the dichloride, CIOH8C12, is obtained as a yellow liquid by acting with hydrochloric acid and potassium chlorate; the solid tetrachloride, Clo Ha C14, results when chlorine is passed into naphthalene dissolved in chloroform. Numerous hydrides are known; heated with red phosphorus and hydriodic acid the hydrocarbon yields mixtures of hydrides of composition Clotho to C1oH2o. Sodium in boiling ethyl alcohol gives the a-dihydride, CloHlo (E. Bamberger, Ber., 1887, 20, p. 1705); and with boiling amyl alcohol the (3-tetrahydride, CIOH12 (E. Bamberger, Ber., 189o, 23, p. 1561). The a-tetrahydronaphthalene is formed when naphthalene is heated with phosphonium iodide at 170°-190° (A. v. Baeyer). Structurally naphthalene may be represented as a fusion of two benzene nuclei, the hydrogen atoms being numbered as in the inset
~\ a
formula	; 1, 4, 5, 8 are a-positions, 2, 3, 6, 7 are
s\/ /a
4
1-5 or 4-8 6diderivatives are ana, whilst 1-8 or 4-5 are peri (see