This carbon rod soldering iron runs on 6 volt battery. The "C" with the open SPST switch is a wood handle with positive wire of battery in one end (positive shown above in simulator) and the brass tube to insert the carbon rod into bottom of wood handle is not shown. Positive terminal connects to sliding ring with set screw to make contact with carbon rod. Closer to tip for hotter temperature settings (3,000 degrees F.) and slide towards wood handle for cooler settings. May be able to weld some things on hottest settings. Work being soldered is connected to Battery ground. Article indicates connections may be reversed.
Micro-projector carbons used in Sun Lamps and scientific instruments are best for small and delicate work.
Also, YouTube soldering iron hack at: https://youtu.be/H8gO_XzKJ7Q
