142 BRITISH OAK GALLS. 
along the Mediterranean Sea, in the part known as 
the Levant, the chief market for it being at Aleppo, 
a town about twenty-five miles inland, in a district of 
the same name; and from this circumstance it is called 
the Aleppo gall. It is the most useful and valu- 
able of all galls. Ink is manufactured from them, 
the process being as follows: The galls are coarsely 
powdered and thoroughly mixed with chopped straw 
to maintain porosity. of the mixture, put into a deep 
narrow oak vat having a perforated false bottom, 
with a tap. Lukewarm water is then poured in, 
and this percolating, extracts and carries the tannin 
of the galls with it; this is drawn off and repeatedly 
run through. <A sufficient quantity of water is 
used, in proportion to the galls, to produce as nearly 
as possible about 50 per cent. of tannin. After fer- 
mentation has taken place the solution is exposed to 
the air, the tannin splitting up into gallic acid and 
sugar. Salt of iron (green vitriol), and gum senegal 
are added. The tannin of the oak gall is different 
from the tannin of the oak bark. 
Another gall, found in certain parts of China, is 
also used in the manufacture of writing ink. It is 
hollow, brittle, irregular in shape, covered externally 
with a grey pubescence. It is caused by an Aphis, 
and contains a rather higher percentage of tannin than 
does the Aleppo gall. Both kinds are of more com- 
mercial value if collected before the insect emerges. 
A gall found in Japan is used for the same purpose. 
It is rich in tannin, but does not:contain so much as 
the former kinds. 
Almost all plants contain tannin, but very few yield 
the kind suitable for ink-making ; the particular kind 
contained in galls is known as gallo-tannic acid. 
Tannin can be dissolved out of plants with a mix- 
ture of spirits of wine and ether. The extract when 
allowed to stand separates into two layers, the lower 
being a strong solution of the tannin. 
