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 l^efore 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 Strono- solution of the tannin. 



