72 
THE TANNINS. 
was the.first to prove this by experiment. In all the 
writings to this time the term “ gallotannic acid” was 
applied to that from oak bark or wood as well as that 
from galls. Stenhouse, by adopting a method used at 
the present time to study the tannins,—namely, by 
heating to decomposition,—found the oak-bark tan¬ 
nin yielded no pyrogallol. The only substance yield¬ 
ing true gallotannic acid was found to be sumac, and 
this, so far as the sumac is concerned, has never been 
disproved. He also showed by experiment that there 
was a distinction between the tannins which produced 
a blue and those which produced a green precipitate 
with iron salts, thereby contradicting several previous 
investigators, as well as the expressed opinion of Ber¬ 
zelius. The subject of iron-bluing and iron-greening 
tannins attracted considerable attention about this time, 
and several other chemists devoted their energies to 
solving the problem of classification by this means, but 
with indifferent success. 
The work of Domine in 1844 has been very exten¬ 
sively quoted, because he offered some improvements 
on the method of Leconnet for preparing tannin. He 
claimed that alcohol was an unnecessary constituent of 
the ether used in extracting galls, but that the presence 
of a small quantity of water was very essential. The 
method proposed was to allow the galls to become sat¬ 
urated with the damp atmosphere of a cellar by expo¬ 
sure of some days, then mix with sufficient ether to 
make a paste, and express, this expression to be re¬ 
peated with ether which had been shaken with six per 
cent, of water. This process was at one time adopted 
by both the United States and British Pharmacopoeias. 
