777 /: TRANSFORMER 



219 



Magnetite arcs require a uni-directional current for their proper 

 operation. (See Chap. XIII, page 431, Par. 196.) In order to 

 obtain this current economically by the use of the constant-cur- 

 rent transformer, mercury-arc rectifiers are used in connection 

 with the transformer. Ordinarily two rectifier tubes are con- 

 nected in series. The diagram of connections for a single recti- 

 fier t u be is shown in Fig. 210. The mercury arc has the property 



110V. A. C. Source 



2200V. A.C.Supply 

 .. 210. Constant-current transformer and mcrrury-.irc rectifier. 



of allowing current to pass in but one direct ion. When current 

 tends to pass in the opposite direction the mercury vapor acts 

 like a valve and prevents its flow. If there were but one circuit 

 through the n-ctiiier the negative half of the wave would be 

 eliminated and the result would be a number of disconnected 

 waves, as shown in Fig. 211 (a). Tin- n-.-titier would not oper- 

 ate under these conditions :i> th- i re would 1:0 out !>< 



I Mini would fail to reestablish it-rlf. l.v u-inu r i wo anodes, 

 a succession of connected waves, Fig. -11 (5), is obtained. 



