Gallic acid contained in the Baris of various Trees, 



ms 



It is to be obferved, that the barks do not keep any refpeftive proportion in the quality 

 of gallic acid and tanning principle contained in each; which is an evidence of the 

 diftinSnefs of principle, and may, perhaps, open a new field of faving oak bark in 

 dying, as the willows, fallow, afli, and others, produce a very fine black. It is alfo 

 ■worthy of obfervation, that the quantities of gallic acid and tanning principle do not 

 differ in equal proportions between the winter and fpring felled oaks. This fafl may 

 lead to the difcrimination of the proper time fdr cutting ; which is, probably, when the 

 fap has completely filled and dilated that part of the vegetable intended for ufe. This 

 will make a difference in the feafon of cutting oak, elm, and other trees, (hrubs, &c. 

 Leaves (hould be taken when arrived at their full fize, and then dried under cover; for 

 as the tanning principle is fo foluble, and the fubflance that contains it fo thin (in a leaf), 

 the dew alone might diffolve it. 



Finally, as the gallic acid does not feem to combine with the matter of fkin, and as 

 its aftringency will corrugate the furface, we may, I think, conclude that its prefence in 

 tanning is not only ufelefs but detrimental. 



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