2l6 



SIMPLE ELECTRIC DEVICES 



first edition, the type being necessarily set afresh. Now, how 

 ever, the type is set up and a mold of it is taken in wax. This 

 mold is coated with graphite to make it a conductor and is then 

 suspended in a bath of copper sulphate, side by side with a slab of 

 pure copper. Current is sent through the solution, until a thin 

 coating of copper has been deposited on the mold. The mold is 

 then taken from the bath, and the wax is replaced by some 

 metal which gives strength and support to the thin copper plate. 

 From this copper plate, which is an exact reproduction of the 

 original type, many thousand copies can be printed. The 

 plate can be preserved and used for later editions. 



