86 THE SCIENTIFIC ASPECTS OF TANNING. 



whilst Dr, Hugo Schiff gives it as his opinion that Tannic acid 

 is an alcoholic, an hydride of gallic acid, bearing a similar relation 

 to gallic acid, as ether has to alcohol,"* which even may be the 

 correct theory : we, as tanners, earnestly hope that our scientific 

 friends may be able to suggest some process by which this 

 decomposition may be arrested, gallic acid being itself quite useless 

 n the process of tanning, Mr. Calvert speaks of carboHc acid, 

 but we cannot altogether corroborate this. 



Divi Divi, '' Cccsalpinia Coriaria^ the pod of a leguminous plant 

 indigenous to the coasts of Venezuela and New Granada. The 

 tree grows to the height of twenty feet : we are not aware that it is 

 cultivated in the least. The dried pod has a burnt appearance, 

 often twisted into the shape of letter S. The quantity which 

 reaches our country averaging about 29,000 tons. It yields from 

 forty to fifty per cent, of tannic acid. 



The tanners of Hungary, Poland, and lower Austria were the 

 principal consumers of D. Divi. But the high prices of 1S66-67, 

 combined with the manifest superiority of the English leather 

 exhibited at the Vienna Exhibition, lead them to turn their atten- 

 tion more to Valonia. The peculiarity of this material being its 

 liability to fermentation after lengthened maceration in the tanpit, 

 •which is almost spontaneous in certain conditions of the weather. 

 It deposits a considerable amount of Bloom, and the tannic acid 

 rapidly changes into gallic. We have found as much as 7.88-grs. 

 of Gallic acid in Too-grs. of powdered D.D. If used in large 

 quantities it gives great weight to the leather, but imparts a dark 

 brown color. We are led to believe that the kind of water 



* Dr. Schiff has proved that Tannic acid is a di-gallate, or rather two atoms 

 of gallic acid less one atom of water, constitute one atom tannic acid. He 

 has converted gallic acid into tannic acid, by removing one atom of water 

 from two atoms of gallic acid. This is accomplished by heating gallic acidL 

 with phosphorus oxytrichloride, which has a great affinity for water. 



Formula of Gallic acid. C- < (Oflo) 



CO OH 



(O 

 / c.c 



