Nation projector carbons (1935)

D.C.. Old Type Low Intensity Lamps Sputtering at the Arc Sputtering at the arc may result from the carbons not being set in the proper position or from operation with too short an arc. A more frequent cause of sputtering, however, is damp carbons. Carbons are porous and tend to absorb any excess of moisture. They are baked at extremely high temperatures in the factory and, when shipped, are thoroughly dry. In shipment, however, they I may be exposed to damp weather or, at the destination, stored in a damp location. Under these conditions, they will absorb sufficient dampness to affect their operation. Carbons should always be kept in a dry place. A great many projectionists have formed the habit of laying a few carbons on top of a rheostat in order to expel any moisture that might have been absorbed after leaving the factory. Others put a trim in the lamp house before burning. Either practice is a good one and is to be recommended since dampness may cause a carbon to chip at the crater as well as sputter at the arc. It should be added here that carbons are not perishable. They are as good ten years after leaving the factory as on the day of shipment. If they have absorbed only water they can be dried out in any suitable manner without their operation being impaired. However, if a chemical has been spilled on them, they may be rendered worthless, depending upon the nature of the chemical. 35 Figure 31 Figure 32