380 CONSIDERATION OF CARBON COMPOUNDS. 



Analytical reactions : 



1. To solution of tannic acid add ferric chloride : a blue-black 

 precipitate falls, soluble in large excess of tannic acid with violet 

 color (Plate VI., 4). 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 gradually 

 lime-water. A white precipitate falls, which on addition of more 

 lime-water becomes blue by reflected, green by transmitted light, and 

 darkens by exposure to air. 



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

 starch, tartar emetic, and most of the alkaloids. 



Naphtalin, C 10 H 8 (Naphtalene). The constitution of all benzene- 

 derivatives considered so far, may be explained by the introduction 

 of radicals in benzene. Naphtalin 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 represented in 

 these formulas : 



H H H OH 



c 



H/ ^O/ W \H H/ C ^C /C W C \H 



i i A : 4 



Naphtalin, C 10 H 8 . Naphtol, QoH^OH. 



Naphtalin 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, naphtalin 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 

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

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

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

 talin is converted into phtalic acid by oxidizing agents. 



Naphtol, C 10 H 7 OH. This compound bears to naphtalin the same 

 relation as phenol to benzene i. e., hydroxyl replaces hydrogen in 

 the respective hydrocarbons. Two isomeric naphtols are known, 



