ARC LAMPS WITH SMALL CURRENTS [Cn. Ill 



For direct current the two carbons must be of different size if the 

 feeding mechanism of the lamp moves the carbons equally. With 

 an equal feeding mechanism, the upper or positive carbon can be 

 7 mm., the lower one 5 mm., or the upper 8 mm. and the lower 

 one 6 mm. 



One could use carbons of the same diameter for direct current, 

 but it would be necessary to feed the upper or positive one more 

 rapidly than the lower one on account of the unequal rate of burn- 

 ing, otherwise the correct relative position of the carbons would 

 not be maintained (fig. 24-25). On a no volt, direct current cir- 

 cuit, the lamp will burn about six minutes without going out. 

 The carbons should be fed up every three to five minutes. 



For alternating current of no volts, the small lamps will burn 

 from eight to ten minutes, sometimes longer. It is well to feed the 

 carbons every five to seven minutes. 



In case a choke-coil is used (Ch. XIII, 736), the lamp burns 

 more quietly and will burn longer without being fed. If a step- 

 down transformer is used, then the right-angled lamp will not burn 

 so long only one to two minutes while a lamp with inclined 

 carbons will burn three minutes, because it takes a higher voltage 

 to maintain the right-angled than the inclined carbon arc (see Ch. 

 XIII, 753, 768). 



TURNING THE ARC LAMP ON AND OFF 



132. Lighting the small arc lamp. For this, make sure that 

 the carbons arc not in contact. Now turn the switch for the room 

 lights and the snap switch in the socket where the separable attach- 

 ment plug for the lamp wiring is screwed in. Feed the carbons 

 together until they touch. There should be a flash of light. 

 Separate the carbons two or three millimeters as soon as the flash 

 is seen and the arc will be established and the light will be at full 

 brilliance. Sometimes it is necessary to keep the carbons almost 

 in contact for a half minute or so, until the tips arc well heated, 

 before the arc will bum. If on separating the carbons the light 

 goes out, they must be brought together again as at first. 



