Gallic acid contained in the Bark of vamusTreei^ 3P3 



fonie experiments to afcerrajn the quantity of tantiing priiicij)le anfl gallic acid, each 

 bark contained. For that purpofe I made ufe of the following methods.i according to 

 the principles laid down by Mr. Segmn. 



By diiiolving an ounce of common glue in two pounds of boiling water, I procured 

 a mucilaginous liquor, which as it contains the matter of (kin in folution, is a tell iot 

 the tanning principle. By a faturated folution of fulphate of iron, I obtained a teft for 

 the Gallic acid. 



I then took one pound of the bark I meant to try, ground as for the life of tanners., 

 and divided it into five parts, each part being put into an earthen veflel. To one part 

 of this bark I added two pounds of water, and infufed them for one hour. Thus 

 I procured an infufion of bark which I poured on the fecond part of the bark, and 

 this ftrengthened infufion again on the third part, and fo on to the fifth. But as a certain 

 portion of the infufioil will remain attached to the zvood of the bark, after the infufion is 

 poured or drawn off, I added a third pound of water to the firft part, and then followed 

 up the infufion on the feveral parts till the three pounds of v;rater, or fo much of them 

 as eould be fepaiated from the bark, were united in the fifth velTel, from which I gene- 

 rally obtained about one pint of ftrong infufion of bark.* 



To a certain quantity of this infufion, I added a given meafure of j the folution of 

 glue ; which fonned an immediate precipitate, that may be feparated from the infufion, 

 by filtering paper. When dried it is a fubftance, formed by the chemical union of 

 the matter of flcin with the tanning principle, and is in faft a powder of leather. By 

 faturating the infufion with the folution of glue, the whole of the tanning principle may 

 be feparated by precipitation. 



For the Gallic Acid. 

 To the pound of bark left in the earthen velTel and already deprived of its tanning 

 principle by thefe quick infufions, I added a given quantity of water to procure a ftrong 

 infufion of the gallic acid which requires a longer time (fay 48 hours). This infufion 

 when Obtained puret affords little figns of the prefence of the tanning principle when 

 tried by the teft of the folution of glue; but with the folution of fulphate of 

 iron it gives a ftrong black colour (the common black dye), which differs in denfity 

 according to the quality of the bark ; this may be further proved by boiling a Ikain of 

 worfted in the dye, by which the gradations of colour will be very perceptibly demon- 

 "flrated. 



* The fpccific gravity of this infufion was afcertaiDed by an hydrometer, whofe gradations are inverfe to thofc 

 of a fpirit hydrometer. 



t It is hardly poffible from the intimate conneflon of the two principles, to feparatethem entirely by infufion ; 

 in the infufion of tanning principle there will always exift a little gallic acid; and in an infufion of gallic acid 

 a little tanning principle will commonly be prefent, unlefs the infiifion of gallic acid is very weak, and procured 

 by a third or fourth watering. 



Having 



