TANNING. 209 



tractive matter is lost to the manufacturer, which 

 might have been made to enter into the composi- 

 tion of his leather. These observations show, that 

 there is some foundation for the vulgar opinion of 

 workmen, concerning what is technically called 

 the feeding of leather in the slow method of tan- 

 ning J and though the processes of the art may in 

 some cases be protracted for an unnecessary length 

 of time, yet, in general, they appear to have ar- 

 rived, in consequence of repeated practical expe- 

 riments, at a degree of perfection which cannot be 

 very flir extended by means of any elucidations of 

 theory that have as yet been known.'* 



As a vast quantity of bark may easily be ob- 

 tained in countries that are covered with natural 

 forests, such as many parts of America, New Hol- 

 land, &c. it has been suggested, as a method of 

 lessening the expense of freight in bringing it over, 

 to make an extract from the bark, which might be 

 very easily transported, and which would serve the 

 purpose of the tanner as well as the bark itself. 



It was first suspected by Sir Joseph Banks, and 

 afterwards confirmed by the experiments of Sir 

 Humphry Davy, that a substance called catechu, or 

 terra Japonica, brought from the East Indies, con- 

 tained a vast quantity of tannin ; so much so, that 

 it far excels every other known substance in this 

 respect, Onepoun.-l of catecliu contains as much 

 tannui as eight or ten pounds of common oak bark, 

 and would consequently tan proportionately as 

 much more leather. It is an extract made from the 

 wood of a species of mimosa, by decoction and sub- 

 sequent evaporation. 



Oak bark being a very expensive article in the 

 process of tanning, various substances have been 

 proposed as substitutes for it. All the parts of ve- 



VOL. ]I, p 



