INK-GALLS. 495 



pearance, inasmuch as the staining liquid is really ink, though 

 of a paler hue than that which is used for writing. A little 

 lemon-juice will soon discharge the colour, and then the soap 

 and water will remove the last remnants of the stain. 



Ink is made by mixing a solution of the sulphate of iron 

 (properly called green vitriol or copperas) with a decoction of 

 certain oak-galls. Perhaps I may mention that a " decoction " 

 signifies water in which any substance has been submitted to 

 boiling heat, but not dissolved. Tea, for example is, when pro- 

 perly made, a decoction of the leaf, though when made with hot, 

 but not boiling water, it has no right to the name. The solution 

 of copperas is only pale green, and that of the gall is nearly 

 colourless, although when mixed, they become deeply black. 

 The old practical joke of forcing a dupe to stain his hands and 

 face black, depended on the knowledge of these properties. 



Before the victim went to wash his hands, some of the decoc- 

 tion of galls was poured into the water, while the towel with 

 which he was supplied had been damped with the copperas solu- 

 tion and then dried. The consequence of this combination was, 

 that although the hands and face might be washed perfectly 

 clean, yet as soon as they were dried with the prepared towel 

 the union of the two substances produced ink, and both hands 

 and face were deeply stained. 



Now when a gall is cut with a knife, the slightly acid juice 

 acts upon the steel, and so a kind of ink is produced, which is 

 pale, but still a veritable ink. There is a well-known method of 

 secret writing which depends on this property of iron and tannin, 

 the principle contained in the galls. 



A quill pen is dipped in the solution of copperas, and the 

 required message is written, usually between the lines or among 

 the words of a letter on imimportant subjects, so as to avoid the 

 suspicions which would be aroused by a sheet of blank paper. 

 The almost colourless solution leaves no mark, and the letter 

 passes without comment, until it reaches the person who is in 

 the secret He pouis some decoction of galls into a wide and 

 flat vessel, and warily dips the letter into it, so as to wet it ; or 

 he saturates a cloth with the decoction, and lays the letter upon 

 it. The tannin then acts upon the solution of iron, ink is formed 

 by their combination, and the formerly invisible words imme- 

 diately become plain and legible. 



