CHEMICAL EFFECTS 



315 



FIG. 206. Ah electric pad serves the 

 same purpose as a hot water bag. 



when everything is in readiness, the ends of the wire are 

 attached to the poles of a distant battery and the heat de- 

 veloped in the wire ignites the 

 fuse. 



292. Welding of Metals. 

 Metals are fused and welded by 

 the use of the electric current. 

 The metal pieces which are to 

 be welded are pressed together 

 and a powerful current is passed 

 through their junction. So 

 great is the heat developed that 

 the metals melt and fuse, and 

 on cooling show perfect union. 



293. Chemical Effects. The Plating of Gold, Silver, and 



Other Metals. If strips of lead or rods of 

 carbon are connected to the terminals of 

 a voltaic cell, as in Figure 208, and are 

 then dipped into a solution of copper sul- 

 phate, the strip in connection with the neg- 

 ative terminal of the cell soon becomes thinly 

 plated with a coating of copper. If a solu- 

 tion of silver nitrate is used in place of the 

 copper sulphate, the coating formed will be 

 of silver instead of copper. So long as the 

 current flows and there is any metal present 

 in the solution, the coating continues to 

 form on the negative electrode, and becomes 

 thicker and thicker. 



The process by which metal is taken out 

 of solution, as silver out of silver nitrate and 

 copper out of copper sulphate, and is in turn deposited as a 

 coating on another substance, is called electroplating. An 



FIG. 207. An in- 

 candescent electric 

 bulb. 



