ton.ifituent. Parts ofcstringent Vegclables. 297 



in the 100 parts, of 59 parts of gelatine and 41 of tannin ; 

 that from the infusion 'of Leicester willow bark, of 5" parts 

 of gelatine and 43 of tannin ; and that from the infusion of 

 Spanish chestnut bark, of Cl parts of gelatine ami 39 of 

 tannin. 



Two pieces of calf-skin, which w'cighcd when dry 120 

 grains each, were tanned ; one in the strongest infusion of 

 Leicester willow bark, and the other in the strongest infu- 

 sion of oak bark. The process was completed, in both in- 

 stances, in less than a fortnight ; when the weight of tlie 

 leather formed by the tannin of the Leicester willow bark 

 was found e(iual to 161 grains, and that of the leather 

 formed by the infusion of oak bark was equal to 164 

 grains. 



When pieces of skin ^^■ere suffered to remain in small 

 quantities of the infusions of the oak bark, and of the Lei- 

 cester willow bark, till they were exhausted of their tanning 

 principle, it was found, that though the residual liquors 

 gave olive-coloured precipitates with the solutions of sul- 

 phate of iron, yet they were scarcely rendered turbid by 

 solutions of muriate of tin ; and there is evciy reason to 

 suppose that a portion of their extractive matter had been 

 taken up with the tannin by the skin. 



I attempted, in different modes, to obtain uncombined 

 gallic acid from the solid matter produced by the evapora- 

 tion of the barks, but without success. When portions of 

 this solid matter were exposed to the degree of heat that is 

 Required for the production of gallic acid from Aleppo galls, 

 no crystals were formed ; and the fluid that came o\'er gave 

 only a brown colour to the solution of salts of iron, and 

 was found to contain much acetous acid and empyreumatic 

 oil. 



When pure water was made to act, in successive por- 

 tions, upon oak bark in coarse powder, till all its soluble 

 parts were taken up, the quantities of liquor last obtained, 

 though they did not act much upon solution of gelatine, or 

 perceptibly redden litmus paper, produced a dense black 

 with the solution of sulphate of iron : by evaporation, they 

 furnished a brown matter, of wlilch a part was rendered 

 insoluble in water by the action of the atmosphere; atid the 

 part soluble in water was not in any degree taken up by sul- 

 phuric ether ; so that, if it contained gallic acid, it was in a 

 Ktate of intimate union with extractive matter. 



Two pieces of culf-skin, which weighed when dry 94 

 grains each, were slowly tanned ; <me by being exposed to 

 » weak infusion of the Leicester w illow bark, and the other 



by 



