ell Sorts of Hides and Skins. Q.I 



IS to fay, with the bark of certain trees, of oak for inftance, 

 cut fmal], bruifed, or ground to a coarfe powder. Pour water 

 on the tan in the firft digefter, where it may ftand foine time, 

 or be drawn off immediately. This liquor is to be poured on 

 the tan in the fecond digefter, and drawn off as before ; then 

 on the tan in the third digefter, and fo on until it comes 

 through the tan in the fifth and lafl. The liquor is theu 

 highly coloured, and marks from fix to eight degrees on the 

 hydrometer for falts. This liquor is to be ufed for tanning 

 the thickefl hides ; and may, for want of a more charafter- 

 i<lic name, be called the tanning lixivium. It has this pe- 

 culiar property, that if you take a fmall quantity of it in a 

 glafs, and pour on it a few drops of a folution of animal glue, 

 the liquor, which before was clear, becomes turbid, and a 

 whitidi fubftance falls to the bottom of the glafs. The pre- 

 cipitate thus obtained, by means of the folution of glue, is 

 A fure indication that the liquor contains the tanning prin- 

 ciple ; for this reafon, that glue being of the fame nature 

 with the fkins or hides of which it is made, whatever fub- 

 ftance unites itfelf indiflblubly with the former, will do f«' 

 likcwife with the latter. 



This folution is made by difTolving a little common glue 

 in water over a moderate fire : by means of it, not only oak 

 bark, but alfo the bark of feveral other trees, fuch as the 

 plane-tree, cheftnut-tree, the American hemlock-tree, pop- 

 lar, elm, willow, See. as well as divers (hrubs and plants, 

 fuch as myrtle, fliumach, &c. all which I call tan, are found 

 to contain the tanning principle ; and by employing the fo- 

 lution as above, it will, in all cafes, be eafy to afcertain whe- 

 ther any given fubftance contains this principle or not. 



In the courfe of thefe lixiviations two things will be ob- 

 fcrved. i. The liquor runnlna; from tiie firit digefter, at 

 length lofes its colour. If in this Itate you take a tittle of it 

 in a glafs, and repeat the former experiment, the liquor no 

 longer becomes turbid, but remains clear j which fhows it 

 contains no more of the tanning principle : but if you pour 

 into the fame glafs a few drops of a folution of fulphate of 

 iron, the liquor beaomcs thick and black. This liquor is not 

 to be poured on the tan in the fecond digefter, but is to be 

 laid by, and ufed for the drpilation, or taking off the hair or 

 wool, us will be more particularly defcribed hereafter. It is 

 diftinguifhed by the name o{ gallic lixivium, becaufe it ap- 

 pears to contain the fame principles as galls. 



Thr liquid fulphate of iron is obtained by difTolving a fmall 

 quantity of iron m oil of vitriol diluted with water, or by dif- 

 folving grecu copper as in water. This folution ferves to afcer- 



B 3 tain 



