282 TANNINS 



4. Lime water added to an aqueous solution of pyrogallol 

 produces a purple colour which rapidly becomes brown. 



5. Solutions of pyrogallol give no precipitate with gelatine. 



6. Potassium cyanide gives a reddish-brown coloration, 

 which turns brown, but the red tint becomes apparent again 

 on shaking. 



PHLOROGLUCINOL. C8H3(OH)3. 

 OH 



HO l^^ y OH 



Phloroglucinol 



Phloroglucinol, which is isomeric with pyrogallol, is pro- 

 duced by fusing a number of substances, such as catechin, 

 kino, dragon's blood, anthocyanins, etc., with potash, and 

 likewise from a number of glucosides, such as phloretin, 

 phloridzin, hesperidin, etc. It crystallizes with 2 molecules 

 of water, but loses them if heated to 100°, and melts at 218° ; 

 it dissolves readily in water, forming a sweet solution, and is 

 readily soluble in alcohol or ether. 



Reactions. 



1. Phloroglucinol is precipitated from solution by lead 

 acetate. 



2. It gives with ferric chloride a bluish-violet colour. 



3. A solution of phloroglucinol in hydrochloric acid pro- 

 duces a red colour on a pine wood shaving ; this reaction 

 can also be made use of for detecting lignified cell walls 

 (p. 229). 



4. It is a reducing agent, and reduces Fehling's solution. 



In addition to the above-mentioned phenols, which are 

 products of the decomposition of tannins by heat or by fusion 

 with alkalis, there are other important substances produced 

 by acid hydrolysis, namely, gallic and ellagic acids and the 

 phlobaphenes. 



