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XV. Experiments to determine the Quantity of tanning Principle 
and gallic Acid contained in the Bark of various Trees . By 
George Biggin, Esq. Coynmunicated by the Right Hon. Sir 
Joseph Banks, Bart. K. B. P. R. S. 
Read June 6 , 1799. 
The bark of trees contains the astringent principle, called gallic 
acid, and also that principle which has a peculiar affinity to the 
matter of skin, and which, from the use to which it is applied, 
is called the tanning principle. But, in the present mode of 
tanning, bark is applied in mass to the skins; consequently, 
both principles are applied. It remains for examination, whether 
both principles are useful in the process of tanning; for, if they 
are not both useful, probably one is detrimental. 
To a nobleman, whose zeal on every occasion by which the 
sciences or arts may receive illustration or improvement is emi- 
nently conspicuous, and to whose public energy, as well as pri- 
vate friendship, I feel myself much indebted, to his Grace the 
Duke of Bedford, I owe the means of prosecuting some expe- 
riments on this subject. His Grace, by collecting a variety of 
barks, at Woburn, gave me an opportunity of making some ex- 
periments to ascertain the quantity of tanning principle and 
gallic acid each bark contained. For that purpose, I made use 
of the following methods, according to the principles laid down 
by M. Seguin. 
