BENZENE SERIES. AROMATIC COMPOUNDS. 587 



If ferric chloride is added in excess, the black precipitate dissolves in 

 it with green color. 



2. Add a few drops of potassium hydroxide : a brown coloration 

 results. 



3. To a dilute solution (1 in 100) of tannic acid add a small quan- 

 tity of lime-water. A pale bluish-white, flocculent precipitate is 

 formed, which is not dissolved on shaking (difference from gallic acid), 

 but becomes more copious and of a deeper blue than pinkish by the 

 addition of an excess of lime-water. 



4. Tannic acid precipitates solutions of gelatin, albumin, gelatinized 

 starch, tartar emetic, and most of the alkaloids. 



The Naphthalene series. 



Naphthalene, Naphthalenum, C 10 H 8 = 127.10. The constitution 

 of all benzene derivatives considered so far may be explained by the 

 introduction of radicals in benzene. Naphthalene and its derivatives 

 must be assumed to be formed by the union of two benzene residues 

 in such a way that they have two carbon atoms in common, as repre- 

 sented in these formulas : 



H H H OH 



H \ C A C A C / H 



<J <!! <" 



P/*\0/ W \0/\H H/ H c / \c^ \H 



j. i A 1 



Naphthalene, Ci H 8 . Naphthol, Ci H T .OH. 



Naphthalene has been mentioned as a product of the destructive distillation 

 of coal, and is obtained from that portion of coal-tar which boils between 180 

 and 220 C. (356 and 428 F.). This distillate is treated with caustic soda and 

 then with sulphuric acid and distilled with water vapor. 



When pure, naphthalene forms colorless, lustrous crystalline plates, having 

 a penetrating, but not unpleasant, odor and a burning, aromatic taste. It fuses 

 at 80 C. (176 F.), and boils at 218 C. (424 F.), but volatilizes slowly at ordi- 

 nary temperature, and readily with water vapor. It is only sparingly soluble 

 in water, but easily soluble in alcohol, ether, chloroform, etc. Impure naph- 

 thalene assumes, when exposed to light, a reddish or brownish color. Naph- 

 thalene is converted into phthalic acid by oxidizing agents. 



Derivatives of naphthalene. While benzene yields only one kind 

 of mono-substitution product, naphthalene yields two varieties in 

 every case. Thus, there are two mono-hydroxy derivatives (naph- 



