Chemistry and Chemical Arts. 125 
gradually forced down the allonge by the superior stratum of ether, 
which operates in this case like a piston. 
Pure tannin is colorless and without odor. It is largely soluble 
in water, the solution reddening turnsole. It decomposes the al- 
kaline carbonates with effervescence, and forms with most of the 
metallic solutions, precipitates which are true tannates. The proto- 
salts of iron are not decomposed by it; but it precipitates abundant- 
ly, and of a deep blue color, the per-salts of this metal. Alcohol 
and ether dissolve tannin, but much less perfectly than water. I 
is incapable of crystallization. A concentrated solution of tannin is 
abundantly precipitated white, by muriatic, nitric, phosphoric, and 
arsenic acid, but is not affected by the oxalic, tartaric, acetic, lactic, 
citric, succinic, selenious or sulphureous acids. \ Nitric acid treated 
with tannin, decomposes it with rapidity, and converts it into oxalic 
acid. Tannin poured into a solution of gelatine in excess, produces 
a white precipitate, which is opaque, soluble especially if warm, in 
the supernatant liquor; but on the contrary, if the tannin is in ex- 
cess, the precipitate resembles elastic membrane, in form, and is 
much less soluble. 
Tannin forms with skin a compound absolutely insoluble; and it 
is possible by the following method to learn whether it is pure or 
mixed with gallic acid; leave the tannin to be tested, for some hours 
in contact with a piece of skin, whose hair has been removed by 
lime, agitating it from time to time, then filter the solution; if the 
tannin is pure, the liquid does not produce the slightest discoloration 
with the per-salts of iron, whereas if it contains gallic acid, in the 
slightest proportions, a deep blue color will appear. This experi- 
ment proves that the matter of the skin is not identical with gelatine. 
annin consists of 
Corban. as 5) 0.5118 18 atoms or equivalents, 
Hydrogen . . 0.0418 18. « sa 
eygei. i. rh AS oe 
A solution of tannin may be preserved indefinitely without altera- 
tion in a closed vessel ; but with the contact of air, it absorbs oxygen 
giving off an equal volume of carbonic acid, and is converted into 
crystallized gallic acid. Lt ge 
ure gallic acid is not affected by a solution of gelatine. It crys- 
tallizes in long, silky needles of a slightly acid, and styptic taste ; and 
Tequires one hundred parts of cold water for its solution. It is more 
soluble still in alcohol, and a little less so in ether. It forms in the 
