10 
THE TANNINS. 
the presence of a substance in certain vegetable infu¬ 
sions, which, when mixed with “green vitriol,” pro¬ 
duces “a deep black liquor, of most extensive use for 
dyeing and staining black. The power by which they 
produce this blackness and their astringency, or that 
by which they contract an animal fibre, seem to de¬ 
pend upon one and the same principle, and to be pro¬ 
portional to one another.” “ Of the properties of this 
colouring and astringent matter, little more is known 
than that it is dissolved and extracted from the subject 
both by water and spirit of wine, and that it does not 
exhale in the evaporation of the liquors by heat.” 
English writers on tannin usually ascribe to Dr. 
Lewis the honor of having a part in its discovery, but 
further than for writing the above quotation of facts, 
which were well known before his time, it is unreason¬ 
able to give him credit. 
He was followed by other investigators, chiefly on 
galls and oak-bark, especially in the relation of the 
latter to tanning, which gradually led to the discovery 
of gallic acid by Scheele in 1786. 
Diz6 in 1791 repeated Scheele’s experiments on galls, 
obtaining similar results; but he went further, and 
separated what he called a resinous substance by means 
of ether. It was unchanged on exposure to air, pos¬ 
sessed an herbaceous taste, dissolved readily in water, 
and this solution formed a white precipitate with sul¬ 
phuric acid. 
Two years later, in 1793, Deyeux, a French chemist 
and apothecary, published a memoir giving the results 
of an elaborate series of experiments, preceded by a 
description of the Aleppo and some other varieties of 
