INK-GALLS. 121 
letter upon it. The tannin then acts upon the solution of 
iron, ink is formed by their combination, and the formerly 
invisible words immediately become plain and legible. 
A decoction of oak-bark would make ink, though of 
inferior quality, and so would tea, inasmuch as the tea- 
leaf contains a large amount of tannin. In fact, when- 
ever the ink in the bottle becomes thick, it can always 
be restored by adding to it a little strong tea, which 
not only gives the requisite liquidity, but does so without 
affecting the blackness, which would probably be the 
case if simple water were added. 
The two principal ingredients of the ink which is 
in common use are sulphate of iron and the galls of 
a species of oak which grows in large quantities in the 
Levant. They are technically termed Aleppo galls, and 
are divided into several classes, according to their value. 
Besides these two ingredients a little gum is added, 
in order to give consistency, and a very little corrosive 
sublimate or creosote, to prevent the growth of -mould. 
The proportions are generally six ounces of pounded 
galls, four ounces of copperas, and four ounces of gum 
arabic to six pints of water. 
In the upper left hand corner of the illustration two 
of these galls are seen upon a branch of the oak. 
They are necessarily much reduced in size, their 
ordinary dimensions being about equal to those of 
Cynips Kollari. For the purposes of trade they are 
divided into black, blue, green, and white galls. The 
last-mentioned class of galls includes those from which 
the insects have escaped, and which are consequently 
weakened in astringency. They are so called because 
they assume a paler hue than the three first classes, 
in which the insect still remains. In shape, the ink- 
gall is nearly spherical, with a slight tendency to a 
Q 
