NAPHTHOL, in chemistry, a substance de rived from naphthalene in the same way that phenol is derived from benzene.— that is, by replacing one of the hydrogen atoms of the hydrocarbon by a molecule of hydroxyl, OH. Its chemical name is hydroxynaphthalene. The empirical formula for naphthalene being Ci.H4, the corresponding formula for naphthol there fore is In benzene the substitution can be made in only one way, because the mole cule of that substance is chemically symmetri cal, its hydrogen atoms being all similarly re lated to one another, and to the carbon atoms. In naphthalene, however, two essentially dif ferent kinds of substitution are possible, ac cording to the position of the hydrogen atom that is replaced. This will be understood by reference to the structural formula of naphtha lene, as presented herewith. The hydrogen atoms in the positions marked aa" are more directly associated with the central pair of car bon atoms than are those in the positions marked Cl); and we must therefore admit that two chemically different naphthols are possible, according as the hydrogen that is replaced by hydroxyl is an ea" atom or a ab" atom. These two naphthols are in fact known, and to dis tinguish them from each other the prefixes 'alpha' and (beta' are attached to the name. Thus 'alpha-naphthol' is the compound ob tained by replacing one of the "a* hydrogen atoms by OH, and 'beta-naphthol' is the com pound obtained by a similar replacement of a 'b' atom. Both of the naphthols resemble ordi
nary phenol (or carbolic acid), and both are used as antiseptics and also in the.preparation of certain of the coal-tar colors. The naphthols ex ist in coal-tar in very small quantities in the fractions made at a high boiling point and may also be prepared by the action of fuming sul phuric acid upon naphthalene, followed by treat ment with sodium hydroxide. In the making of a naphthol the sulphuric acid treatment is con ducted at a temperature ranging from 175° to 190° F. For B-naphthol the temperature is kept at 390° F. Alpha-naphthol crystallizes in short lustrous monoclinic needles, which melt at 201' F. and boil at 543° F. Beta-naphthol crystallizes in flat plates or tablets, melts at F. and boils at 547' F. Both are slightly soluble in hot water, and both dissolve freely in alcohol, ether and benzene. The solution of A-naphthol in water has a violet color; that of B-naphthol a yellow color. The naphthol derivatives of most value in the arts are their sulphonic acids, and di-sulphonic acids, and the tri-sulplionic acid of A-naphthol, and chromo trope acid or chromogen; all used in the pro duction of coal-tar dyes.