RECTIFYING DEVICES 



395 



If the starting switch S is closed, a current will flow from 

 D to C, the magnitude of which is limited by the resistance 

 R. Now, if the tube is tipped back, the mercury bridge 

 connecting C and D is broken and the rupturing of the cur- 

 rent causes a slight arc, which is sufficient to produce the 

 initial ionization of the mercury vapor. 



Starting Resistance for Load. To make the tube start 

 readily a starting resistance R f controlled by the switch 

 S' } is first used as a load. After the tube has operated 



"IMMMii 



FIG. 261. Connection Diagram for the Ordinary Mercury Rectifier, 

 Showing Starting Anode. 



through this artificial load for a few seconds, it becomes 

 warmed and the battery may then be connected in the 

 circuit and the starting resistance cut out. Of course, the 

 switch S, controlling the starting anode D, is also opened 

 as soon as the tube is operating properly. 



124. Application of the Mercury Arc Rectifier. The 

 two principal applications of the mercury arc rectifier are 

 ior charging storage batteries and for operating c-c. arc 

 lamps from a-c. mains. 



