TANNING MATTER, fcCi 25 



1. 



One hundred grains of galls reduced to powder were Experiments, 



infused with four ounces of water, and part of the infusion f-^* °° f" ^^'*'* 



7 ^ licial substance 



upon the addition of solution of isinglass afforded (as havingthe cha- 



usual) a copious precipitate of a brownis^h-white colour, racters of tan- 



A quarter of an ounce of nitrio acid was added to one ^ 

 onnce of the above infusion, which then, was not in any 

 manner affected by the dissolved isinglass. 



% • ' 



One hundred grains of the same galls were slightly 

 roiisted, and being digested with four ounces of water, 

 formed a brown liquor, which was filtrated. 



Solution of isinglass was then added to a part of the 

 above liquor, and produced a precipitate not very unlike 

 the former, but much less in quantity. 



After this, a quarter of an ounce of nitric, acid was 

 added to one ounce of the same liquor, and some dissolved 

 isinglass was subsequently p(»ared into it, by which it was 

 rendered turbid, and a small portion of a dark brown 

 precipitate was produced, resembling that which is com- 

 monly afforded by the artificial tanning substance. 

 3. 



The remainder of the above mentioned liquor, with the 

 rcsiduun\of the roasted galls, were digested with a quar- 

 ter of an ounce of nitric acid until the whole had become 

 dry. Water was then poured upon it, and formed a dark 

 brown solution, which yielded a copious brown precipi- 

 tate by the addition of dissolved isinglass. 



From these experiments on galls it appears, that the 

 natural tannin contained in them is destroyed by nitric 

 acid; that the tannin is also diminished, (and I may add,) 

 is ultimately destroyed by the process of roasting; that 

 when galls have not been so far roasted as to destroy the 

 whole of the tannin, then the remainder of this seems to 

 be destroyed by the addition of nitric acid, Avhilst at the 

 same time a small portion of the artificial tanning sub- 

 stance is produced ; and that this last is always plentifully 

 afforded by roasted galls when digested with nitric acid, 

 similar to other vegetable bodies when thus treated. 



These remarks are also partly confirmed by the follow- 

 ing experiments upon oak bark. * 



Vol. XV.— Sept. 1806. E Two 



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