PHENOLIC CONSTITUENTS 279 



2. With ferric chloride it gives a green colour which is 

 changed to violet on the addition of sodium acetate. 



3. Like pyrogallol it reduces silver nitrate in the cold and 

 has therefore been used as a photographic developer. 



4. It reduces Fehling's solution on warming. 



RESORCINOL. CeHilOH)^. 

 OH 



OH 

 Resorcinol 



This is isomeric with catechol ; it does not generally occur 

 in tannins * but in certain resins, notably galbanum resin and 

 asafoetida. 



It is used commercially in the manufacture of dye-stuffs, 

 and when heated with sodium nitrite gives the indicator 

 known as Lacmoid. 



Resorcinol crystallizes from benzene in colourless needles 

 and melts at 1 19° ; it is somewhat soluble in water, the solution 

 having a sweetish taste. 



Reactions. 



1. It is not precipitated from solution by lead acetate. 



2. With ferric chloride it gives a dark violet colour which 

 is destroyed by the addition of sodium acetate. 



3. It reduces ammoniacal silver nitrate or Fehling's solution 



on warming. 



HYDROQUINONE. CbH,(OH),. 

 OH 



OH 

 Hydroquinone 



This third isomer of the formula C6H4(OH)2 likewise is 

 not found in tannins, but occurs combined with glucose in the 

 glucoside arbutin and uncombined in the leaves and flowers of 



* According to Nierenstein, it is produced together with protocatcchuic 

 acid and phloroglucinol from quebracho tannin by potash fusion. 



