308 INK-MAKING. 



fire, and afterwards filter it while hot. Put it again 

 over the fire, and dissolve in it, first, half an ounce 

 of gum arabic, and afterwards of alum and white 

 sugar, each half an ounce. 



Printing Ink. 



[ Printers' ink is a black paint composed of lamp- 

 black and linseed or suet oil boiled, so as to acquire 

 considerable consistence and tenacity. The art of 

 preparing it is kept a secret; but the obtaining good 

 lamp-black appears to be the chief difficulty in 

 making it. 



The ink used by copper-plate printers, differs 

 from the last only in the oil not being so much 

 boiled, and the black which is used being Frank- 

 fort black. 



Sympathetic Inks. 



Sympathetic inks are such as do not appear 

 immediately after they are written with, but which 

 may be made to appear at pleasure, by certain 

 means. A variety of substances have been used 

 for this purpose. We shall describe the best 

 of them. 



1. Dissolve some sugar of lead in water, and 

 write with the solution. When dry, no writing 

 will be visible. When you want to make it appear, 

 wet the paper with a solution of alcaline sulphuret 

 (liver of sulphur), and the letters will immediately 

 appear of a brown colour. Even exposing the 

 writing to the vapours of these solutions will render 

 it apparent. 



2. Write with a solution of gold in aqua regia, 

 and let the paper dry gently in the shade. Nothing 



