526 



RHEOSTATS AND OTHER BALLAST 



[CH. XIII 



wire are then covered by a burlaps sac so that there can not be a 

 metallic contact between the masses of metal. This upper wire 

 and its iron are then immersed in the barrel. If now the arc lamp 

 is fitted with carbons, and the switch closed the arc will form as 

 usual, the salt water and the iron plates serving as a rheostat. 



wt ._ wi 



W2 



FIG. 282. SALT WATER RHEOSTAT. 



W lt W a Conductors. One end of conductor W, is connected to an iron 

 plate P 3 in the bottom of the dish. The other end is connected to the plate P, 

 which is suspended by a string wound around the clamp. The burlaps sack S, 

 prevents contact of P f and P, with resulting short circuit should the upper 

 plate be let down too far. It is safer still to have both plates covered, and 

 the container must be of wood, glass or stoneware, i.e. some non-conductor. 



The jar contains a %% solution of salt. The resistance is regulated by 

 raising or lowering the plate P,. If more current is required, lower the upper 

 plate, if less current, raise P, so that the two plates will be farther apart. 



