CLASSIFICATION 287 



and chestnut wood tannin and sumach, divi-divi, myrobolans, 

 valonia, and algarobilla. 



These tannins have the following characteristics : — 



1. They give with ferric salts a blue-black coloration. 



2. They give no precipitate with bromine water. 



3. They produce on leather a " bloom " consisting of 

 ellagic acid. 



(B) Catechol tannins, including all the pine barks, acacias, 

 mimosas, oak barks (but not oak wood, fruits or galls), 

 quebracho wood, cassia and mangrove barks, canaigre, cutch, 

 and gambler. 



The tannins of this class are characterized by the following 

 properties : — 



1. They give with iron alum a greenish-black colour, 

 though the reaction is liable to be rendered uncertain by the 

 presence of other colouring matters. 



2. When treated with bromine water, until the solution 

 smells strongly of it, they give a yellowish or brown precipi- 

 tate ; in weak solutions the precipitate may form slowly. 



3. The addition of concentrated sulphuric acid to a drop 

 of the infusion produces a dark red or crimson ring at the 

 junction of the two liquids ; on dilution the hquid turns pink. 



4. These tannins deposit no " bloom," but when boiled 

 with acids deposit red insoluble colouring matters known as 

 phlobaphenes (see p. 297). 



5. Some of the tannins belonging to the pyrocatechol group, 

 notably gambler and cutch, contain phloroglucinol as one 

 of their constituents ; this substance may be tested for by 

 moistening a pine wood shaving with a little of the infusion 

 and then adding a little concentrated hydrochloric acid ; the 

 formation, after a short time, of a bright red or purple stain 

 indicates the presence of phloroglucinol. (This is an adapta- 

 tion of the so-called lignin reaction.) 



Procter's classification should not be regarded as abso- 

 lutely rigid, but it receives some support from the reaction 

 of Stiasny * according to which pyrocatechol tannins are 

 * Stiasny : " Der Gerber," 1905, 186. 



