THE 
LONDON, EDINBURGH anv DUBLIN 
PHILOSOPHICAL MAGAZINE 
AND 
JOURNAL OF SCIENCE. 
(THIRD SERIES.} 
JUNE 1843. 
LXIX. On some Astringent Substances as Sources of Pyro- 
gallic Acid. By Dr. Joan STENHOUSE.* 
HEMISTS have usually divided the varieties of tannin 
which occur so abundantly in the vegetable kingdom, 
into two kinds; those which give black and those which 
give green precipitates with salts of iron. ‘The propriety of 
this distinction has of late been called in question by Ber- 
zelius, who seems to think that the tannic acid in all plants is 
essentially the same; and that the green and gray colours of 
the precipitates with salts of irori are owing to the presence 
of free acid. Professor Liebig appears also to hold a similar 
opinion. Berzelius states at 116th of his Rapport Annuel 
for 1841, on the authority of C. H. Cavallius, “ that the tan- 
nic acids which give green precipitates with sulphate of iron, 
give blue precipitates with acetate of iron, and that their green 
combinations are rendered blue by the addition either of small 
quantities of acetate of lead, by a little alkali, or even by a 
great excess of gelatine.” He also states that the lead com- 
pounds of those species of tannin which give green precipitates 
with salts of iron are rendered blue by the addition of a little 
sulphate of iron. He likewise affirms that when a solution of 
any of the tannins which give green precipitates remains in 
contact for some time with chips of iron, a blue instead of a 
green precipitate is obtained, and that its blue colour is 
changed to green by the addition of acetic acid. These state- 
ments have induced Berzelius to conclude that the giving 
green or black precipitates with salts of iron is not a distinctive 
character for any species of tannin, as these precipitates are 
convertible into each other; bases rendering them black or 
* Communicated by the Chemical Society; having been read Novem- 
ber 15, 1842. 
Phil. Mag. 8. 3. Vol. 22, No. 147. June1843. 2F 
