[ 74 ] 

 XV. Process for preparing pure Gallic Acid. By 



M. RiCHTER*. 



JLnfuse in cold water one pound and a half of gall nuts, 

 previously reduced to fine powder, taking care frequently to 

 agitate the mixture. Pass the liquid through a cloth ; add 

 water to the pulp which refuses to go through, and again 

 put it through the cloth, using a press to separate the wa- 

 ter. Join the liquors, and with a c:ent!e heat evaporate 

 them, and a matter of a dark brown colour, and very brittle, 

 will be obtained. 



Pure alcohol poured on this matter, reduced to a fine 

 powder, acquires a pale straw colour. The deposit infused 

 again in alcohol communicates but little colour to it. The 

 brown residuum now left is composed almost wholly of 

 pure tannin. 



Mix the two alcoholic extracts, which distil in a small 

 retort to one eighth. What remains will be almost a solid 

 mass. Pour water to it, and expose it to a gentle heat, and 

 you will obtain a clear and almost colourless solution. 



Evaporate tliis solution, and you will obtain from it vx'ry 

 small, white, prismatic crystals. The liquor furnishes 

 more, but they are commonly a little coloured. It is suf- 

 ficient to levigate them with water to obtain them verv 

 white. By this process half an ounce of crystals is procured 

 from one pound of gallsj these crystals are extremely light, 

 and consequently occupy a considerable space. They pos- 

 sess the following properties : 



1. They are less soluble in water than in alcohol. Dis- 

 solved in water they redden tincture of turnsole. They 

 combine witli alkaline carbonates, separating from them 

 the carbonic acid. 



2. These alkaline gallates form black precipitates in so- 

 lutions of iron, and likewise decompose all other metallic 

 solutions. But if a solution of pure gallic acid be added to 

 a neutral and perfectly clear solution of iron, no change of 

 colour takes place till the solution of iron is decomposed bv 

 the external air, which by oxidating the iron still more, and 

 forming a sulphate of iron of a different nature, more fa- 

 vourable to the combination of the gallic acid with the 

 oxide of iron in excess, produces a black colour. If to a 

 solution of iron you add oxide of iron recently precipitated, 

 you immediately obtain a black precipitate. The same re- 



• From the Annates de CAimie, vol. lii. 



• suh 



