588 CONSIDERATION OF CARBON COMPOUNDS. 



thol), two mono-amino derivatives (naphthylamine), etc. This is 

 exactly what would be expected if the formula for naphthalene given 

 above be true. The 8 hydrogen atoms in the molecule fall into two 

 groups of 4 each, the atoms of each group bear the same relation to the 

 molecule, but different from the relation that the atoms of the other 

 group bear. This is shown in the following formulas, in which the 

 hydrogen atoms are designated in a manner that permits of reference 

 in the formulas for the derivatives of naphthalene : 



Ha 3 Ha 8H HI 



/3 3 H .a X Hj3 7H (X H2 



\ c / \ c / 



o 



x^C s /G^ /C\ ^C\ 



\H3 



II II 



Ha' 2 Ha 1 H 5 H 4 



In the first formula, hydrogen atoms , a 1 , a 2 , a 3 are alike, and , 

 /5 1 , /5 2 , /5 s are alike, but bear a different relation from that of the a 

 hydrogen atoms. In the second formula, the corresponding groups 

 are 1, 4, 5, 8 and 2, 3, 6, 7. The mono-substitution products in which 

 the a hydrogen is replaced, are known as alpha- or a-derivatives, the 

 others as beta- or ^-derivatives. 



Theoretically, the number of di- and tri-substitution products of 

 naphthalene is very large. Thus, ten di-chlor and fourteen tri-chlor 

 derivatives are possible, and all are known. Such facts as these leave 

 very little doubt as to the truth of the structural formula of naphtha- 

 lene as given above. 



Naphthol, C 10 H 7 OH = 142.98. This monatomic phenol bears to 

 naphthalene the same relation as phenol to benzene /. <?., hydroxyl 

 replaces hydrogen in the respective hydrocarbons. Two isomeric 

 naphthols, the alpha- and beta-naphthol, are known, which differ in 

 their physical properties and in their physiological action. The 

 naphthol which is used medicinally is beta-naphthol, a solid compound 

 crystallizing in thin, shining plates, having an odor similar to phenol 

 and a sharp, pungent taste. It fuses at 122 C. (252 F.), boils at 

 286 C. (547 F.), is soluble in about 1000 parts of cold, or 75 parts 

 of boiling, water ; and readily soluble in alcohol, ether, chloroform, 

 and fatty oils. The aqueous solution is colored greenish by ferric 

 chloride. A few drops of iodine solution added to an aqueous solution 

 of beta-naphthol, followed by an excess of alkali solution, should pro- 



