BENZENE SERIES. AROMATIC COMPOUNDS. 577 



then reddish-brown and dark-brown color. Nitric acid also colors it 

 yellow, then brown, and this property is made use of in testing for 

 traces of nitric acid. Solutions of silver, gold, and mercury are 

 reduced by pyrogallol even in the cold. 



Gallacetophenone or Gallactophenone, ^^< 3 obtained by 



heating a mixture of pyrogallol, zinc chloride, and glacial acetic acid to 148 

 C. It is a crystalline powder of dirty flesh-color, soluble in water, introduced 

 to replace pyrogallol, which is poisonous. 



Phloroglucinol, C 6 H 3 (OH) 3 . 1:3:5 (Phloroglucin, Symmetrical trihy- 

 droxy-benzene), results when resorcin and several resins, as gamboge, dragon's 

 blood, etc., are fused with potassium hydroxide. It forms colorless prisms, 

 melting at 218 C., very soluble in water and alcohol, and of a sweet taste. It 

 stains lignin red and, together with vanillin, is used to detect hydrochloric acid 

 in stomach contents. 



Hydroxy-hydroquinone, C 6 H 3 (OH) 3 . 1 : 2 : 4, is the third trihydroxy- 

 benzene. It is an interesting fact that according to the theory as to the struc- 

 ture of the benzene molecule, three isomeric dihydroxy-benzenes and trihy- 

 droxy-benzenes should exist, and in each case three actually do exist. 



Most of the phenols give colors with ferric chloride solution, and are acted 

 on by the oxygen of the air with formation of colored bodies. They are un- 

 stable toward oxidizing agents, forming in many cases carbon dioxide. The 

 di- and trihydroxyl derivatives are less stable than the simple phenols. The 

 same is true also of hydroxy acids of benzene, for example, salicylic and gallic 

 acids. 



Aromatic alcohols and aldehydes. 



Aromatic alcohols. These are aromatic derivatives of the fatty alcohols 

 i e., alcohols in which hydrogen of the fatty hydrocarbon residue is replaced by 

 a benzene derivative. The aromatic alcohols have the properties of true fatty 

 alcohols. 



Benzyl alcohol, CJJ^CH V OH, is the simplest member of the class; it is 



isomeric with cresol, C 6 H 4 <Q^ 3 , but has entirely different properties. Benzyl 



alcohol is found in balsam of Peru and Tolu, mostly in combination with ben- 

 zoic or cinnamic acid. 



Aromatic aldehydes. These are aromatic derivatives of the fatty alde- 

 hydes and behave in all respects like the latter ; thus they combine readily 

 with oxygen to form acids and behave generally like unsaturated compounds. 



Benzaldehyde, Benzaldehydum, C 6 H 5 .COH = 1O5.25. This is 

 the simplest one of the aromatic aldehydes, and is produced artificially 

 or obtained from natural oil of bitter almonds or other oils. It is a 

 colorless, strongly refractive liquid, having a bitter-almond-like odor. 

 It is easily converted into benzoic acid by oxidation. 



37 



