TAJSTNIC ACIDS. 425 



from Chinese gall-nuts) are macerated with 12 parts 

 ether and 3 parts alcohol for two days, the mixture 

 being frequently shaken ; the solution is then poured 

 off, and the residue again treated in the same way with 

 the same quantity of ether and alcohol. To the united 

 extracts 12 parts of water are added; the alcohol and 

 ether distilled off over a water bath ; the solution fil- 

 tered ; and the filtrate evaporated to dryness. 



Colorless amorphous mass, of a purely astringent 

 taste; inodorous; easily soluble in water; reddens lit- 

 mus. It forms bluish-black precipitates with solutions 

 of ferric salts. It is thrown down from its solution by 

 mineral acids and a number of alkaline salts (sodium 

 and potassium chlorides, not by saltpetre and sodium 

 sulphate); most thoroughly by a solution of gelatin and 

 by animal membranes. Further, it precipitates most 

 organic bases, starch, albumen. Tribasic acid. Its 

 salts are amorphous and difficult to obtain of constant 

 composition. The solutions of the alkaline salts be- 

 come colored red or brown rapidly in the air, oxygen 

 being taken up and the acid decomposed. The free 

 acid in an aqueous solution is also decomposed in the 

 air. If a concentrated extract of gall-nuts is allowed 

 to stand in contact with the air, gallic acid is deposited 

 from it, mixed with another crystalline acid, ellagic 

 acid, C 14 H 6 p 8 + 2H 2 0. This is very difficultly soluble 

 in water ; it is also formed by heating two molecules 

 gallic acid with one molecule arsenic acid in aqueous 

 solution, and is the principal ingredient of a known in- 

 testinal concretion, bezoar, found in a species of goat 

 of Persia. 



By boiling with dilute acids, it is resolved into sugar 

 and gallic acid (p. 360) ; also by boiling with alkalies 

 (only in the latter case the sugar undergoes further de- 

 composition); and also by the action of yeast, emulsin, 

 or a ferment contained in gall-nuts. 



Heated alone it yields pyrogallic acid (p. 310). 



Catechutannic acid. In catechu, a dark or light 

 brown extract prepared from Acacia catechu, Areca 

 catechu, and Nauclea gambir. Very similar to gallo- 



36* 



